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    BibTeX-Key Author / Editor / Organization Title Year Journal / Proceedings / Book BibTeX type Keywords
    Vos1984 Vos, M.; Marel, D. van der. & Sawatzky, G.A. Auger line shape in alloys 1984 Physical Review B
    Vol. 29 (6) , pp. 3073-3084  
    article
    BibTeX:
    @article{Vos1984,
      author = {M. Vos and D. van der Marel and G. A. Sawatzky},
      title = {Auger line shape in alloys},
      journal = {Physical Review B},
      publisher = {American Physical Society (APS)},
      year = {1984},
      volume = {29},
      number = {6},
      pages = {3073--3084},
      doi = {https://doi.org/10.1103/physrevb.29.3073}
    }
    					
    Vos1989 Vos, M.; Xu, F.; Anderson, S.G.; Weaver, J.H. & Cheng, H. Photoemission studies of interface chemistry and Schottky barriers for ZnSe(100) with Ti, Co, Cu, Pd, Ag, Au, Ce, and Al 1989 Physical Review B
    Vol. 39 (15) , pp. 10744-10752  
    article
    BibTeX:
    @article{Vos1989,
      author = {M. Vos and F. Xu and Steven G. Anderson and J. H. Weaver and H. Cheng},
      title = {Photoemission studies of interface chemistry and Schottky barriers for ZnSe(100) with Ti, Co, Cu, Pd, Ag, Au, Ce, and Al},
      journal = {Physical Review B},
      publisher = {American Physical Society (APS)},
      year = {1989},
      volume = {39},
      number = {15},
      pages = {10744--10752},
      doi = {https://doi.org/10.1103/physrevb.39.10744}
    }
    					
    Simpson1991 Simpson, P.J.; Vos, M.; Mitchell, I.V.; Wu, C. & Schultz, P.J. Ion-beam-induced damage in silicon studied using variable-energy positrons, Rutherford backscattering, and infrared absorption 1991 Physical Review B
    Vol. 44 (22) , pp. 12180-12188  
    article
    BibTeX:
    @article{Simpson1991,
      author = {P. J. Simpson and M. Vos and I. V. Mitchell and C. Wu and P. J. Schultz},
      title = {Ion-beam-induced damage in silicon studied using variable-energy positrons, Rutherford backscattering, and infrared absorption},
      journal = {Physical Review B},
      publisher = {American Physical Society (APS)},
      year = {1991},
      volume = {44},
      number = {22},
      pages = {12180--12188},
      doi = {https://doi.org/10.1103/physrevb.44.12180}
    }
    					
    Storer1994 Storer, P.; Caprari, R.S.; Clark, S.A.C.; Vos, M. & Weigold, E. Condensed matter electron momentum spectrometer with parallel detection in energy and momentum 1994 Review of Scientific Instruments
    Vol. 65 (7) , pp. 2214-2226  
    article
    BibTeX:
    @article{Storer1994,
      author = {P. Storer and R. S. Caprari and S. A. C. Clark and M. Vos and E. Weigold},
      title = {Condensed matter electron momentum spectrometer with parallel detection in energy and momentum},
      journal = {Review of Scientific Instruments},
      publisher = {AIP Publishing},
      year = {1994},
      volume = {65},
      number = {7},
      pages = {2214--2226},
      doi = {https://doi.org/10.1063/1.1144730}
    }
    					
    Vos1995 Vos, M. & McCarthy, I.E. Observing electron motion in solids 1995 Reviews of Modern Physics
    Vol. 67 (3) , pp. 713-723  
    article
    BibTeX:
    @article{Vos1995,
      author = {M. Vos and I. E. McCarthy},
      title = {Observing electron motion in solids},
      journal = {Reviews of Modern Physics},
      publisher = {American Physical Society (APS)},
      year = {1995},
      volume = {67},
      number = {3},
      pages = {713--723},
      doi = {https://doi.org/10.1103/revmodphys.67.713}
    }
    					
    Vos2000 Vos, M.; Cornish, G.P. & Weigold, E. High-energy (e, 2e) spectrometer for the study of the spectral momentum density of materials 2000 Review of Scientific Instruments
    Vol. 71 (10) , pp. 3831-3840  
    article e,2e spectroscopy; solids; electrons; graphite; carbon; films
    Abstract: A new spectrometer for the study of energy-resolved momentum densities is described. The (e, 2e) spectrometer uses a symmetric configuration and uses incoming energies up to 50 keV. Energy resolution and momentum resolution are 1.8 eV and 0.1 a.u., respectively. Compared to previous spectrometers this spectrometer has rather low levels of multiple scattering, and thus allows for more quantitative analysis of the data and/or the measurement of thicker samples.
    BibTeX:
    @article{Vos2000,
      author = {Vos, M. and Cornish, G. P. and Weigold, E.},
      title = {High-energy (e, 2e) spectrometer for the study of the spectral momentum density of materials},
      journal = {Review of Scientific Instruments},
      year = {2000},
      volume = {71},
      number = {10},
      pages = {3831--3840},
      url = {http://link.aip.org/link/?RSI/71/3831}
    }
    					
    Vos2000a Vos, M. & Weigold, E. Developments in the measurement of spectral momentum densities with (e,2e) spectrometers 2000 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 112 (1-3) , pp. 93-106  
    article electronic-structure; thin-films; spectroscopy; solids; energy; scattering; aluminum; graphite; carbon; oxide
    Abstract: The introduction of multiparameter high energy electron momentum spectroscopy (EMS) spectrometers, with high energy and momentum resolution and coincidence count rates, has made it possible to obtain detailed information on the electronic structure of condensed matter and surfaces. In particular it gives direct information on the spectral-momentum density of the material under study, which may be a single crystal, polycrystalline, or amorphous. The first such spectrometer, the Flinders University spectrometer, uses asymmetric kinematics in the measurement of the energies and momenta of the two outgoing electrons in the (e,2e) collision. The new ANU spectrometer uses symmetric kinematics and much higher energies. It is therefore less affected by deleterious multiple-scattering events. On the other hand the Flinders spectrometer is surface sensitive, whereas the ANU spectrometer is more bulk sensitive. Some aspects of EMS measurements of condensed-matter specimens and the performance of the two spectrometers are discussed.
    BibTeX:
    @article{Vos2000a,
      author = {Vos, M. and Weigold, E.},
      title = {Developments in the measurement of spectral momentum densities with (e,2e) spectrometers},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2000},
      volume = {112},
      number = {1-3},
      pages = {93--106},
      url = {http://dx.doi.org/10.1016/S0368-2048(00)00204-8}
    }
    					
    Kheifets2001 Kheifets, A.S.; Vos, M. & Weigold, E. The spectral momentum density of aluminium, copper and gold measured by electron momentum spectroscopy 2001 Zeitschrift Fur Physikalische Chemie
    Vol. 215 , pp. 1323-1339  
    article compton-scattering
    Abstract: Electron momentum spectroscopy (EMS) gives direct information of the full energy-resolved electron momentum densities of occupied states (bands) in solidssingle crystal, polycrystalline or amorphous. Here we present data from a new high energy EMS spectrometer using 50keV incident and 25keV outgoing electrons, on polycrystalline specimens of aluminium, copper and gold. The spectral momentum densities show very significant electron-electron correlation effects which are in good agreement with many-body Green's function calculations.
    BibTeX:
    @article{Kheifets2001,
      author = {Kheifets, A. S. and Vos, M. and Weigold, E.},
      title = {The spectral momentum density of aluminium, copper and gold measured by electron momentum spectroscopy},
      journal = {Zeitschrift Fur Physikalische Chemie},
      year = {2001},
      volume = {215},
      pages = {1323--1339},
      url = {http://dx.doi.org/10.1524/zpch.2001.215.10.1323}
    }
    					
    Sattler2001 Sattler, T.; Tschentscher, T.; Schneider, J.R.; Vos, M.; Kheifets, A.S.; Lun, D.R.; Weigold, E.; Dollinger, G.; Bross, H. & Bell, F. Anisotropy of the electron momentum density of graphite studied by (gamma,e gamma) and (e,2e) spectroscopy 2001 Physical Review B
    Vol. 63 (15) , pp. 155204  
    article single-crystal graphite; x-ray fluorescence; band-structure; inverse photoemission; compton-scattering; spectrometer; mechanism; surface; solids
    Abstract: The electron momentum density (EMD) of two different modifications of graphite has been measured and the results of the measurements have been compared with theoretical calculations from three different theories: a full potential linear muffin-tin orbital, a modified augmented plane wave, and a pseudopotential calculation. Experimental results have been obtained by two different methods. The complete three-dimensional EMD is determined by inelastic photon-electron scattering, i.e., by the so-called (gamma ,e gamma) experiment, and by electron-electron scattering, the (e,2e) experiment, cuts in the spectral electron momentum density are studied. For the (gamma ,e gamma) experiment 180 keV synchrotron radiation from the PETRA storage ring at the Deutsches Elektronen-Synchrotron has been used with coincident detection of the recoil electrons. The (e,2e) experiments were carried out at the new (e,2e) spectrometer at the Australian National University using 40 keV primary electron energy and simultaneous detection of the outgoing electrons in an equal energy sharing mode. As samples we have prepared approximately 20 nm thin self-supporting graphite foils either by thermal evaporation (TE) or by laser plasma ablation (LPA). They are thin enough to suppress in essence electron multiple scattering. Electron diffraction analysis revealed that the LPA foil contains graphitic basal planes with a random distribution of c axes, whereas the TE foil was strongly c-axis oriented in the sense that the basal planes were parallel to the foil surface. In the analysis of the results special attention was devoted to anisotropies in the EMD revealed by comparison of TE and LPA foils. The (e,2e) measurements showed furthermore a strong orientation dependence of the intensity of pi and sigma states (here we have for comparison additionally measured highly oriented pyrolytic graphite). The EMD's obtained by both techniques show anisotropies in the momentum distribution of graphite and are discussed in view of the theoretical results.
    BibTeX:
    @article{Sattler2001,
      author = {Sattler, T. and Tschentscher, T. and Schneider, J. R. and Vos, M. and Kheifets, A. S. and Lun, D. R. and Weigold, E. and Dollinger, G. and Bross, H. and Bell, F.},
      title = {Anisotropy of the electron momentum density of graphite studied by (gamma,e gamma) and (e,2e) spectroscopy},
      journal = {Physical Review B},
      year = {2001},
      volume = {63},
      number = {15},
      pages = {155204},
      url = {http://link.aps.org/abstract/PRB/v63/e155204}
    }
    					
    Vos2001 Vos, M.; Kheifets, A.S. & Weigold, E. The spectral momentum density of aluminum measured by electron momentum spectroscopy 2001 Journal of Physics and Chemistry of Solids
    Vol. 62 (12) , pp. 2215-2221  
    article compton-scattering; e,2e experiments; energy; solids; spectrometer
    Abstract: Electron momentum spectroscopy is a tool ideally suited for the study of energy-resolved momentum densities. Here we present new data from a high-energy EMS experiment using 50 keV incoming and 25 keV outgoing electrons. Both the measured energy distributions and the measured momentum distributions are affected by multiple scattering. However, after correcting for these effects, neither distribution can be fully understood using electronic structure calculations that take electron-electron correlation into account only on a mean-field level.
    BibTeX:
    @article{Vos2001,
      author = {Vos, M. and Kheifets, A. S. and Weigold, E.},
      title = {The spectral momentum density of aluminum measured by electron momentum spectroscopy},
      journal = {Journal of Physics and Chemistry of Solids},
      year = {2001},
      volume = {62},
      number = {12},
      pages = {2215--2221},
      url = {http://dx.doi.org/10.1016/S0022-3697(01)00180-9}
    }
    					
    Vos2001a Vos, M.; Kheifets, A.S. & Weigold, E. Momentum profiles of aluminum 2001 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 114 , pp. 1031-1036  
    article energy; spectrometer; solids
    Abstract: Electron momentum spectroscopy is a tool ideally suited for the study of the energy-resolved momentum densities. Here we present new data from a high-energy EMS experiment using 50 keV incoming and 25 keV outgoing electrons. Momentum profiles have been measured from a thin aluminum film for the 2p core level and the valence band near E,. The resolution of these momentum profiles, as well as the effects of multiple scattering are discussed. It is found that the high-energy EMS experiment measures momentum densities with superior resolution and very little background.
    BibTeX:
    @article{Vos2001a,
      author = {Vos, M. and Kheifets, A. S. and Weigold, E.},
      title = {Momentum profiles of aluminum},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2001},
      volume = {114},
      pages = {1031--1036},
      url = {http://dx.doi.org/10.1016/S0368-2048(00)00284-X}
    }
    					
    Vos2001b Vos, M.; Kheifets, A.S.; Weigold, E. & Aryasetiawan, F. Electron correlation effects in the spectral momentum density of graphite 2001 Physical Review B
    Vol. 63 (3) , pp. 033108  
    article cumulant expansion; e,2e experiments; solids; scattering; aluminum
    Abstract: The spectral function of an annealed evaporated carbon film was measured using a high-energy (e,2e) spectrometer. Interpretation of these data was relatively straightforward due to low levels of multiple scattering. Large lifetime broadening and strong asymmetries were found in the observed line shapes, with tails extending to large binding energies. A conventional band-structure calculation within the frame of the density functional theory failed to describe the observed intensity. However it could be described well using a calculation of the spectral function based on the cumulant expansion to the single-particle Green's function. Neither the theory nor the experiment showed indications of well-defined intrinsic plasmon structures.
    BibTeX:
    @article{Vos2001b,
      author = {Vos, M. and Kheifets, A. S. and Weigold, E. and Aryasetiawan, F.},
      title = {Electron correlation effects in the spectral momentum density of graphite},
      journal = {Physical Review B},
      year = {2001},
      volume = {63},
      number = {3},
      pages = {033108},
      url = {http://link.aps.org/abstract/PRB/v63/e033108}
    }
    					
    Vos2002 Vos, M. Detection of hydrogen by electron Rutherford backscattering 2002 Ultramicroscopy
    Vol. 92 (3-4) , pp. 143-149  
    article energy-loss spectroscopy; radiation-damage
    Abstract: A novel method for detection of hydrogen by an electron beam in extremely thin samples is described. Elastically scattered electrons impinging with 20-30 keV on a thin formvar film were detected at a scattering angle near 45degrees. In these large momentum transfer elastic collisions a clear separation of the signal of hydrogen and heavier elements was found. By changing the momentum transfer we can verify that the hydrogen signal is not due to inelastic energy loss contributions. The width of the hydrogen elastic peak is much larger than the elastic peaks due to heavy elements (carbon and oxygen). The ratio of the hydrogen elastic peak and the main elastic peak is smaller than expected by 30-50% depending on the energy of the impinging electron. This could be due to electronic excitations directly coupled to the elastic collision. The stability of the formvar film under electron radiation was studied. A reduction in thickness of the film with increasing fluence, as well as the preferential depletion of hydrogen, was found. Possible improvements of the experimental configuration for this type of experiments are discussed.
    BibTeX:
    @article{Vos2002,
      author = {Vos, M.},
      title = {Detection of hydrogen by electron Rutherford backscattering},
      journal = {Ultramicroscopy},
      year = {2002},
      volume = {92},
      number = {3-4},
      pages = {143--149},
      url = {http://dx.doi.org/10.1016/S0304-3991(02)00127-4}
    }
    					
    Vos2002a Vos, M. Observing atom motion by electron-atom Compton scattering 2002 Physical Review A
    Vol. 65 (1) , pp. 012703  
    article neutron
    Abstract: A very elemental method of observing the motion of the nucleus in molecules or solids is described. The observations for copper, graphite, and formvar films can be understood assuming that the electrons scatter from a moving target (vibrating atoms). The method is the complete electron analog for neutron Compton scattering. The nuclear motion causes a doppler shift in the energy of elastically scattered electrons. It is rather unusual among the methods of studying vibrations (e.g., molecular vibrations in individual molecules or phonons in solids) in that the information obtained is directly related to the momentum distribution of the probed atoms, rather than the energy difference between different vibrational states. The application of the semiclassical picture described here could fail to describe more detailed measurements. Gas-phase experiments may be more suitable for fully quantitative measurements. Indeed the experiment could be used to study the breakup of molecules after a well-defined perturbation.
    BibTeX:
    @article{Vos2002a,
      author = {Vos, M.},
      title = {Observing atom motion by electron-atom Compton scattering},
      journal = {Physical Review A},
      year = {2002},
      volume = {65},
      number = {1},
      pages = {012703},
      url = {http://link.aps.org/abstract/PRA/v65/e012703}
    }
    					
    Vos2002b Vos, M.; Kheifets, A.S.; Sashin, V.A.; Weigold, E.; Usuda, M. & Aryasetiawan, F. Quantitative measurement of the spectral function of aluminum and lithium by electron momentum spectroscopy 2002 Physical Review B
    Vol. 66 (15) , pp. 155414  
    article resolution compton-scattering; band-structure; photoemission; density; li; na; oxidation; surface; solids; metals
    Abstract: We present measurements of the spectral function of aluminum and lithium using high-energy electron momentum spectroscopy. For aluminum the quasiparticle peaks show clear asymmetries and significant satellite intensity that extends over a wide region to larger binding energies. The intensity distribution is not well described by band structure calculations. These data are described only by calculations based on the many-body cumulant expansion scheme. The measured momentum distribution at the Fermi level agrees with the theoretical one within 0.03 a.u. For lithium a bandwidth of 3.0 eV is obtained.
    BibTeX:
    @article{Vos2002b,
      author = {Vos, M. and Kheifets, A. S. and Sashin, V. A. and Weigold, E. and Usuda, M. and Aryasetiawan, F.},
      title = {Quantitative measurement of the spectral function of aluminum and lithium by electron momentum spectroscopy},
      journal = {Physical Review B},
      year = {2002},
      volume = {66},
      number = {15},
      pages = {155414},
      url = {http://link.aps.org/abstract/PRB/v66/e155414}
    }
    					
    Vos2002c Vos, M. & Weigold, E. Particle-in-a-box momentum densities compared with electron momentum spectroscopy measurements 2002 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 123 (2-3) , pp. 333-344  
    article aluminum; molecules; orbitals; solids; atoms
    Abstract: We investigate the momentum space representation of the solutions of a particle in a three-dimensional box. By comparing the calculated momentum densities of a particle in a box with the measured distribution of highly symmetric molecules we want to elucidate the nature of the measured orbitals. Finally the measured momentum distribution of a free electron metal is compared with the results of this model.
    BibTeX:
    @article{Vos2002c,
      author = {Vos, M. and Weigold, E.},
      title = {Particle-in-a-box momentum densities compared with electron momentum spectroscopy measurements},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2002},
      volume = {123},
      number = {2-3},
      pages = {333--344},
      url = {http://dx.doi.org/10.1016/S0368-2048(02)00031-2}
    }
    					
    Chatzidimitriou-Dreismann2003 Chatzidimitriou-Dreismann, C.A.; Vos, M.; Kleiner, C. & Abdul-Redah, T. Comparison of electron and neutron Compton scattering from entangled protons in a solid polymer 2003 Physical Review Letters
    Vol. 91 (5) , pp. 057403  
    article hydrogen
    Abstract: We present, for the first time, a direct comparison between electron (ECS) and neutron (NCS) Compton scattering results from protons of a solid polymer. The momentum distributions of hydrogen obtained from ECS and NCS are in excellent agreement. In both experiments, a strong "anomalous" shortfall in the scattering intensity of protons first detected in liquid water with NCS [C. A. Chatzidimitriou-Dreismann et al., Phys. Rev. Lett. 79, 2839 (1997)] is found ranging from about 20% up to 50%, depending on the momentum transfer applied. The characteristic times of electron- and neutron-proton collisions lie in the subfemtosecond range. The presented ECS and NCS results provide further direct evidence for this striking effect, which has been ascribed to attosecond quantum entanglement of the protons.
    BibTeX:
    @article{Chatzidimitriou-Dreismann2003,
      author = {Chatzidimitriou-Dreismann, C. A. and Vos, M. and Kleiner, C. and Abdul-Redah, T.},
      title = {Comparison of electron and neutron Compton scattering from entangled protons in a solid polymer},
      journal = {Physical Review Letters},
      year = {2003},
      volume = {91},
      number = {5},
      pages = {057403},
      url = {http://link.aps.org/abstract/PRL/v91/e057403}
    }
    					
    Kheifets2003 Kheifets, A.S.; Sashin, V.A.; Vos, M.; Weigold, E. & Aryasetiawan, F. Spectral properties of quasiparticles in silicon: A test of many-body theory 2003 Physical Review B
    Vol. 68 (23) , pp. 233205  
    article angle-resolved photoemission; electron momentum densities; single-crystal; band-structure; semiconductors; metals; si; approximation; exchange; solids
    Abstract: The spectral function A(q,omega) of silicon has been measured along a number of symmetry directions using high-energy high-resolution electron momentum spectroscopy. It is compared with first-principles calculations based on the interacting one-electron Green's function which is evaluated in the GW and the cumulant expansion approximations. Positions of the quasiparticle peaks (dispersion), their widths (lifetimes), and the extensive satellite structures are measured over a broad range of energies and momenta. The band dispersions are well described by both calculations, but the satellite predicted by the GW calculation is not observed. Unlike the GW calculation, the cumulant expansion calculation gives a significantly better description of the shape and momentum dependence of the satellite structure, presenting a promising approach for studying high-energy excitations.
    BibTeX:
    @article{Kheifets2003,
      author = {Kheifets, A. S. and Sashin, V. A. and Vos, M. and Weigold, E. and Aryasetiawan, F.},
      title = {Spectral properties of quasiparticles in silicon: A test of many-body theory},
      journal = {Physical Review B},
      year = {2003},
      volume = {68},
      number = {23},
      pages = {233205},
      url = {http://link.aps.org/abstract/PRB/v68/e233205}
    }
    					
    Vos2003 Vos, M.; Kheifets, A.S.; Sashin, V.A. & Weigold, E. Influence of electron diffraction on measured energy-resolved momentum densities in single-crystalline silicon 2003 Journal of Physics and Chemistry of Solids
    Vol. 64 (12) , pp. 2507-2515  
    article compton-scattering; spectroscopy; graphite; solids
    Abstract: Electron momentum spectroscopy is used to determine the spectral function of silicon single crystals. In these experiments 50 keV electrons impinge on a self-supporting thin silicon film and scattered and ejected electrons emerging from this sample with energies near 25 keV are detected in coincidence. Diffraction effects are present that give rise to additional structures in the measured spectral momentum densities. Spectra for a specific momentum value can be obtained at different orientations of the crystal relative to the analysers. By comparing these spectra for which the measured momentum density is the same, but the diffraction conditions of the incoming and outgoing electron trajectories differ, one can distinguish between features due to diffraction of the incoming and/or outgoing electrons, and those due to the electronic structure of the target itself.
    BibTeX:
    @article{Vos2003,
      author = {Vos, M. and Kheifets, A. S. and Sashin, V. A. and Weigold, E.},
      title = {Influence of electron diffraction on measured energy-resolved momentum densities in single-crystalline silicon},
      journal = {Journal of Physics and Chemistry of Solids},
      year = {2003},
      volume = {64},
      number = {12},
      pages = {2507--2515},
      url = {http://dx.doi.org/doi:10.1016/j.jpcs.2003.08.004}
    }
    					
    Bowles2004 Bowles, C.; Kheifets, A.S.; Sashin, V.A.; Vos, M. & Weigold, E. The direct measurement of spectral momentum densities of silicon with high energy (e, 2e) spectroscopy 2004 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 141 (2-3) , pp. 95-104  
    article compton-scattering; electron; solids; e,2e; spectrometer; diffraction; coincidence; states
    Abstract: Electron momentum spectroscopy is a coincidence technique that measures the spectral momentum density of matter. In this paper we outline the theoretical framework underlying these measurements, give a description of the spectrometer, and show in detail the information this technique can provide for the prototypical material silicon. We present results for single crystals as well as amorphous samples, describe the influence that diffraction and inelastic multiple scattering have on these measurements. The results are compared with full-potential linear-muffin-tin-orbital (FP-LMTO) calculations (for dispersion), and many-body calculations (for line shapes).
    BibTeX:
    @article{Bowles2004,
      author = {Bowles, C. and Kheifets, A. S. and Sashin, V. A. and Vos, M. and Weigold, E.},
      title = {The direct measurement of spectral momentum densities of silicon with high energy (e, 2e) spectroscopy},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2004},
      volume = {141},
      number = {2-3},
      pages = {95--104},
      url = {http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=811&Issue=1}
    }
    					
    Vos2004 Vos, M.; Bowles, C.; Kheifets, A.S.; Sashin, V.A.; Weigold, E. & Aryasetiawan, F. Measurement of the electronic structure of crystalline silicon by electron momentum spectroscopy 2004 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 137-40 , pp. 629-632  
    article solids
    Abstract: Electron momentum spectroscopy (EMS) is a scattering experiment that determines the spectral function of a sample, i.e. the density of electrons as a function of binding energy and momentum. Here, it is used to study the spectral function of silicon single crystals in the extended zone scheme. Two symmetry directions and four intermediate directions are measured. The relation between the band index and the main observed momentum component is discussed. The observed peak shapes are compared with many-body calculations based on the cumulant expansion scheme. The dispersion is described well, but peak shapes agree with many-body theory only on a semi-quantitative level.
    BibTeX:
    @article{Vos2004,
      author = {Vos, M. and Bowles, C. and Kheifets, A. S. and Sashin, V. A. and Weigold, E. and Aryasetiawan, F.},
      title = {Measurement of the electronic structure of crystalline silicon by electron momentum spectroscopy},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2004},
      volume = {137-40},
      pages = {629--632},
      url = {http://dx.doi.org/10.1016/j.elspec.2004.02.051}
    }
    					
    Vos2004a Vos, M.; Kheifets, A.S.; Bowles, C.; Chen, C.; Weigold, E. & Aryasetiawan, F. Electronic structure of copper studied by electron momentum spectroscopy 2004 Physical Review B
    Vol. 70 (20) , pp. 205111  
    article resolution compton-scattering; fermi-surface; noble-metals; muffin-tin; cu; photoemission; densities; diffraction; silicon
    Abstract: We present electron momentum spectroscopy measurements of the electronic structure of copper single crystals. Generally, good agreement was found with the band dispersion as measured by photoemission. The energy-resolved momentum densities are quite anisotropic. Observed diffraction effects can be disentangled in first order, and the experiment compares well to calculated momentum density. Deviations of the Fermi surface from spherical symmetry are resolved by this scattering experiment. Many-body effects cause lifetime broadening of the quasiparticle peak and a smooth tail extending to higher binding energies, but no clear satellite structures were found.
    BibTeX:
    @article{Vos2004a,
      author = {Vos, M. and Kheifets, A. S. and Bowles, C. and Chen, C. and Weigold, E. and Aryasetiawan, F.},
      title = {Electronic structure of copper studied by electron momentum spectroscopy},
      journal = {Physical Review B},
      year = {2004},
      volume = {70},
      number = {20},
      pages = {205111},
      url = {http://link.aps.org/abstract/PRB/v70/e205111}
    }
    					
    Vos2004b Vos, M.; Sashin, V.A.; Bowles, C.; Kheifets, A.S. & Weigold, E. Probing the spectral densities over the full three-dimensional momentum space 2004 Journal of Physics and Chemistry of Solids
    Vol. 65 (12) , pp. 2035-2039  
    article spectroscopy
    Abstract: Electron momentum spectroscopy is often used to determine the spectral function of materials. It relies on the determination of the scattering angle of electrons with extremely high precision. In practice, it is important to calibrate these angles, and hence the momentum scales. Here we describe a method to do so and show how minor misalignments affect the measured momentum densities of Li2O. Using the same procedure we further calibrated the momentum scale by measuring the spectral momentum density along a Brillouin zone boundary of a Si single crystal. (C) 2004 Elsevier Ltd. All rights reserved.
    BibTeX:
    @article{Vos2004b,
      author = {Vos, M. and Sashin, V. A. and Bowles, C. and Kheifets, A. S. and Weigold, E.},
      title = {Probing the spectral densities over the full three-dimensional momentum space},
      journal = {Journal of Physics and Chemistry of Solids},
      year = {2004},
      volume = {65},
      number = {12},
      pages = {2035--2039},
      url = {http://dx.doi.org/10.1016/j.jpcs.2004.08.017}
    }
    					
    Weigold2004 Weigold, E.; Kheifets, A.S.; Sashin, V.A. & Vos, M. Spectral momentum densities in matter determined by electron scattering 2004 Acta Crystalographica Section A
    Vol. 60 , pp. 104-110  
    article e,2e spectroscopy; compton-scattering; graphite; solids; aluminum
    Abstract: In electron momentum spectroscopy (EMS), an incoming energetic electron (50 keV in this work) ionizes the target and the scattered and ejected electrons are detected in coincidence ( at energies near 25 keV). From the energy and momentum of the detected particles, the energy omega and momentum q transferred to the target can be inferred. The observed intensity distribution I(omega, q) is proportional to the spectral momentum density of the target and hence provides a direct challenge to many-body theoretical descriptions of condensed matter. This is illustrated by comparing some many-body calculations with EMS measurements on graphite and polycrystalline aluminium.
    BibTeX:
    @article{Weigold2004,
      author = {Weigold, E. and Kheifets, A. S. and Sashin, V. A. and Vos, M.},
      title = {Spectral momentum densities in matter determined by electron scattering},
      journal = {Acta Crystalographica Section A},
      year = {2004},
      volume = {60},
      pages = {104--110},
      url = {http://journals.iucr.org/a/issues/2004/02/00/issconts.html}
    }
    					
    Chen2005 Chen, C.; Gale, M.N.; Kheifets, A.S.; Vos, M. & Went, M.R. Spectral momentum densities of vanadium and vanadium oxide as measured by high energy (e, 2e) spectroscopy 2005 Journal of Physics-Condensed Matter
    Vol. 17 (48) , pp. 7689-7704  
    article electronic band-structure; x-ray photoelectron; satellite structure; valence shell; solids; silicon; surface
    Abstract: The spectral momentum densities of vanadium metal and V2O3 are measured by electron momentum spectroscopy. Results are compared with band structure calculations based on density functional theory (DFT). Qualitatively, the agreement between theory and experiment is good. The calculated total band width of vanadium metal (6.5 eV) is in excellent agreement with the observed one (6.5 +/- 0.25 eV). The splitting between the outer and inner valence bands in V2O3 is 2 eV larger in the experiment than in the density functional theory calculation. The observed momentum distributions agree reasonably well with the calculated distributions with the exception of the intensity of the outer valence band relative to the inner valence band in V2O3: the outer valence band is less intense than calculated. The momentum density near the Fermi level in V metal resembles that of atomic V 3d orbitals. However, momentum profiles of the V 3d orbitals in V2O3 are much more sharply peaked than the atomic 3d orbital in both the theory and experiment. Correlation effects are discussed and theoretical problems in describing EMS data from narrow band systems are identified.
    BibTeX:
    @article{Chen2005,
      author = {Chen, C. and Gale, M. N. and Kheifets, A. S. and Vos, M. and Went, M. R.},
      title = {Spectral momentum densities of vanadium and vanadium oxide as measured by high energy (e, 2e) spectroscopy},
      journal = {Journal of Physics-Condensed Matter},
      year = {2005},
      volume = {17},
      number = {48},
      pages = {7689--7704},
      url = {http://dx.doi.org/10.1088/0953-8984/17/48/019}
    }
    					
    Kheifets2005 Kheifets, A.; Vos, M.; Cavanagh, S.J. & Kono, M. Proceedings of the Fourteenth International Conference on Vacuum Ultraviolet Radiation PhysicsCairns, Australia, 19th-23rd July, 2004 Preface 2005 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 144 , pp. 1-+  
    misc
    BibTeX:
    @misc{Kheifets2005,
      author = {Kheifets, A. and Vos, M. and Cavanagh, S. J. and Kono, M.},
      title = {Proceedings of the Fourteenth International Conference on Vacuum Ultraviolet Radiation PhysicsCairns, Australia, 19th-23rd July, 2004 Preface},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2005},
      volume = {144},
      pages = {1--+},
      url = {http://dx.doi.org/10.1016/j.elspec.2005.02.006}
    }
    					
    Vos2005 Vos, M.; Bowles, C.; Kheifets, A.S. & Went, M.R. Electron momentum spectroscopy of light and heavy targets 2005 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 149 (1-3) , pp. 20-28  
    article high-energy e; densities; silicon; diffraction; scattering; solids
    Abstract: Electron momentum spectroscopy (EMS) measures the spectral function of electrons in matter directly, provided that multiple scattering effects are negligibly small. Even for the thinnest films this is not the case and one has to correct for multiple scattering effects in order to retrieve the spectral function. Both elastic and inelastic scattering effects affect the measurement. Elastic scattering is expected to increase greatly with increasing atomic number, much more so than inelastic scattering. For this reason EMS was thought to be of limited value for heavy targets. Here, we present data for carbon, silicon and gold and show that they are affected in different ways by multiple scattering. The gold sample has poor count rate, but in the spectra the multiple scattering effects appear rather minor. Carbon and silicon on the other hand have good count rates, but the spectra are strongly affected by multiple scattering. Monte Carlo simulations are used to try to understand these effects. Rather surprisingly the EMS spectra for heavy elements are of comparable quality to those of lighter elements.
    BibTeX:
    @article{Vos2005,
      author = {Vos, M. and Bowles, C. and Kheifets, A. S. and Went, M. R.},
      title = {Electron momentum spectroscopy of light and heavy targets},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2005},
      volume = {149},
      number = {1-3},
      pages = {20--28},
      url = {http://dx.doi.org/10.1016/j.elspec.2005.06.002}
    }
    					
    Vos2005a Vos, M.; Chatzidimitriou-Dreismann, C.A.; Abdul-Redah, T. & Mayers, J. Electron and neutron scattering from polymer films at high momentum transfer 2005 Nuclear Instruments and Methods in Physics Research Section B
    Vol. 227 (3) , pp. 233-250  
    article compton-scattering; quantum entanglement; cross-sections; spectrometer; spectroscopy; polyethylene; spectra
    Abstract: Neutrons have been used in the past to measure Compton profiles of atomic motion. Recently it was found that similar information can be obtained using electron scattering experiments. In particular formvar and polyethylene were studied using both techniques, thus considerably extending the first results reported recently [C.A. Chatzidimitriou-Dreismarm et al., Phys. Rev. Lett. 91 (2003) 57403]. In this paper we review the underlying theoretical framework and compare the experimental realization of both techniques. The various steps required to analyze the data are outlined. Both in the neutron and electron experiments we found anomalous low intensities of the hydrogen contribution to the spectrum.
    BibTeX:
    @article{Vos2005a,
      author = {Vos, M. and Chatzidimitriou-Dreismann, C. A. and Abdul-Redah, T. and Mayers, J.},
      title = {Electron and neutron scattering from polymer films at high momentum transfer},
      journal = {Nuclear Instruments and Methods in Physics Research Section B},
      year = {2005},
      volume = {227},
      number = {3},
      pages = {233--250},
      url = {http://dx.doi.org/10.1016/j.nimb.2004.09.003}
    }
    					
    Vos2005b Vos, M.; Cooper, G. & Chatzidimitriou-Dreismann, C.A. Quasi-elastic scattering of electrons at large momentum transfer 2005 Electron and Photon Impact Ionization and Related Topics 2004
    Vol. - (183) , pp. 81-91  
    article neutron compton-scattering; spectroscopy; spectrometer; polyethylene; shell
    Abstract: Precision measurements of the energy of keV electrons scattered 'elastically' over large angles from solid films or gas-phase molecules show that these electrons have lost some energy. In particular scattering from a system that contains hydrogen and carbon reveals two well-separated elastic peaks. The amount of energy lost in the deflection of the electron depends not only on the mass of the nucleus the electron scattered from, but also on the momentum of this nucleus. We make an estimate of the cross section for these elastic scattering processes. These cross sections do not reproduce the observed intensities very well, in particular the observed hydrogen intensity is for the solid film experiment smaller than expected. With increasing energy loss the time-scale of the collision process decreases. The decrease of the hydrogen cross section is possibly due to quantum correlation effects of the proton at the short timescale of the collision.
    BibTeX:
    @article{Vos2005b,
      author = {Vos, M. and Cooper, G. and Chatzidimitriou-Dreismann, C. A.},
      title = {Quasi-elastic scattering of electrons at large momentum transfer},
      journal = {Electron and Photon Impact Ionization and Related Topics 2004},
      year = {2005},
      volume = {-},
      number = {183},
      pages = {81--91},
      url = {http://bookmarkphysics.iop.org/br_results.htm?ID=54WUVksJpEI9uWAm5P8z29Rg&subjects=131}
    }
    					
    Vos2005c Vos, M. & Went, M. Monte Carlo simulations of small-angle elastic scattering events 2005 Physical Review B
    Vol. 72 (23) , pp. 233101  
    article spectral momentum density; spectroscopy; solids
    Abstract: Quantitative interpretation of electron spectroscopy is almost always dependent on the understanding of multiple scattering effects. Monte Carlo simulations are often used to model multiple scattering effects, as this method provides for a conceptually simple framework for incorporating both elastic and inelastic scattering processes. In this paper, we demonstrate that when small-angle deflections are important, diffraction effects become significant, and straightforward Monte Carlo simulations are not expected to be valid. However, a simple modification to the Monte Carlo procedure is presented that uses cluster-derived elastic scattering cross sections rather than those derived from isolated atoms. In this way we can incorporate diffraction effects in the simulations. Results from electron momentum spectroscopy are presented to illustrate these effects. These modified simulations greatly improve the agreement between experiment and theory, and this approach builds a bridge between Monte Carlo and diffraction-based interpretations of experiments.
    BibTeX:
    @article{Vos2005c,
      author = {Vos, M. and Went, M.},
      title = {Monte Carlo simulations of small-angle elastic scattering events},
      journal = {Physical Review B},
      year = {2005},
      volume = {72},
      number = {23},
      pages = {233101},
      url = {http://link.aps.org/abstract/PRB/v72/e233101}
    }
    					
    Went2005 Went, M.R. & Vos, M. Electron-induced KLL Auger electron spectroscopy of Fe, Cu and Ge 2005 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 148 (2) , pp. 107-114  
    article 3d transition-metals; line-shape analysis; spectra; energy; ni; films; widths; ag
    Abstract: KLL Auger spectra excited by electrons with energies in the 30-35 keV range of Fe, Cu and Ge films were measured, using thin free-standing films. It was possible to obtain spectra with an energy resolution of about 1 eV. The observed spectra can not be described satisfactorily by just the multiplet splitting of the final state as calculated for an isolated atom. Additional features, due in part to intrinsic (shake satellites) and in part to extrinsic (energy loss of the escaping electron) processes formed a large fraction on the observed intensities. In particular a number of distinct satellite structures that are not predicted by the atomic Auger process are observed. For Fe and Cu the satellite peaks can be explained in terms of shake-up processes from the 3d(5/2)-4d(5/2) states. Similar satellite structures observed in Ge are partly attributed to plasmon creation and partly to shake-up processes. It is demonstrated that both the thickness dependence of the observed intensity distributions and transmission electron energy loss measurements contain invaluable information for the interpretation of these spectra. (c) 2005 Elsevier B.V. All rights reserved.
    BibTeX:
    @article{Went2005,
      author = {Went, M. R. and Vos, M.},
      title = {Electron-induced KLL Auger electron spectroscopy of Fe, Cu and Ge},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2005},
      volume = {148},
      number = {2},
      pages = {107--114},
      url = {http://dx.doi.org/10.1016/j.elspec.2005.04.004}
    }
    					
    Bowles2006 Bowles, C.; Went, M.R.; Kheifets, A.S. & Vos, M. Direct measurement of spectral momentum densities of ordered and disordered semiconductors by high energy EMS 2006 AIP Conference Proceedings
    Vol. 811 , pp. 167  
    article ems, si, ge, amorphous
    Abstract: High Energy solid state electron momentum spectroscopy (EMS) is capable of directly measuring spectral functions of ordered and disordered solid matter. In this paper we investigate the spectral functions for the group IV semiconductors Ge and Si. We attempt to resolve the electronic structure differences in amorphous, polycrystalline and crystalline atomic arrangements of the semiconductors. We examine the experimental differences in polycrystalline and amorphous Ge, and draw conclusions as to the similarities/differences between the two states of matter.
    BibTeX:
    @article{Bowles2006,
      author = {C. Bowles and M. R. Went and A. S. Kheifets, and M. Vos},
      title = {Direct measurement of spectral momentum densities of ordered and disordered semiconductors by high energy EMS},
      journal = {AIP Conference Proceedings},
      year = {2006},
      volume = {811},
      pages = {167},
      url = {http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APCPCS000811000001000167000001&idtype=cvips&gifs=yes}
    }
    					
    Nixon2006 Nixon, K.L.; Vos, M.; Bowles, C. & Ford, M.J. Measuring the electronic structure of disordered overlayers by electron momentum spectroscopy: the Cu/Si interface 2006 Surface and Interface Analysis
    Vol. 38 (8) , pp. 1236-1241  
    article ems;silicon;copper;
    Abstract: The Cu-Si interface was studied by electron momentum spectroscopy. A thick disordered interface is formed if one material is deposited on the other. Electron momentum spectroscopy measures intensity as a function of binding energy and target electron momentum. Momentum resolution is demonstrated to be very helpful in interpreting the data, even for these disordered interfaces. The interface layer has a well-defined electronic structure, different from either Si or Cu, and consistent with silicide formation. Information is obtained about the total bandwidth of the interface compound, effective Brillouin zone size and Fermi radius. No clear differences are observed in the electronic structure of the interface layer for Si deposited on Cu or Cu deposited on S.
    BibTeX:
    @article{Nixon2006,
      author = {Nixon, K. L. and Vos, M. and Bowles, C. and Ford, M. J.},
      title = {Measuring the electronic structure of disordered overlayers by electron momentum spectroscopy: the Cu/Si interface},
      journal = {Surface and Interface Analysis},
      year = {2006},
      volume = {38},
      number = {8},
      pages = {1236--1241},
      url = {http://dx.doi.org/10.1002/sia.2385}
    }
    					
    Vos2006 Vos, M.; Bowles, C.; Kheifets, A.S. & Went, M.R. Band structure of silicon as measured in extended momentum space 2006 Physical Review B
    Vol. 73 (8) , pp. 085207  
    article ems;silicon;
    Abstract: Direct measurement of the wave function (or at least the modulus squared of the wave function, the spectral function) is an important goal in electron spectroscopy. This requires a state-selective (i.e., energy resolved) measurement of the momentum density in all of momentum space, not just the reduced Brillouin zone. Photoemission has been used very successfully to measure dispersion, mainly in the reduced zone scheme. Compton measurements determine a projection of the momentum density in the full momentum space, but do not contain energy information. Here we present electron momentum spectroscopy measurements of extremely thin silicon single crystals, that resolve both energy and momentum, not just the reduced momentum. Measurements were done along different lines in extended momentum space, that are equivalent within the reduced zone scheme. For different lines different bands dominate, resulting in dramatic different spectral momentum densities. The observed intensities compare well to the spectral function as obtained by linear muffin tin band structure calculations. The results show a unified picture that forms a bridge between Compton measurements determining densities and photoemission measurements determining dispersion.
    BibTeX:
    @article{Vos2006,
      author = {Vos, M. and Bowles, C. and Kheifets, A. S. and Went, M. R.},
      title = {Band structure of silicon as measured in extended momentum space},
      journal = {Physical Review B},
      year = {2006},
      volume = {73},
      number = {8},
      pages = {085207},
      url = {http://link.aps.org/abstract/PRB/v73/e085207}
    }
    					
    Vos2006a Vos, M. & Went, M.R. Effects of bonding on the energy distribution of electrons scattered elastically at high momentum transfer 2006 Physical Review B
    Vol. 74 , pp. 205407  
    article erbs; graphite;
    Abstract: High resolution measurements of 40 keV electrons scattered over 44.3 deg. from evaporated carbon films are presented. The observed width of the energy distribution of electrons scattered from carbon is significantly larger than the experimental energy resolution, and its position is shifted to lower energy. Measurements were done for transmission and reflection geometries for thin films with thicknesses varying from 90 Å to 1400 AA. The observed peak shape is largely independent of the thickness and measurement geometry. The peak shape deviates from Gaussian in all cases, in a way consistent with theories that describe these processes beyond the impulse approximation. The energy shift of the carbon peak is measured by evaporating a small amount of Au on these films. Separation of the Au and C peak is somewhat smaller than calculated assuming scattering from free C and Au atoms, but independent of measurement geometry. Finally spectra were measured from highly oriented pyrolytic graphite (HOPG) films. Now different widths are observed in reflection geometry and transmission geometry. This is attributed to the anisotropy of the motion of the C atoms in HOPG. Also the Au-C separation is slightly orientation dependent for HOPG. All observations agree at least semi-quantitatively, with neutron Compton scattering results, a related scattering experiment that studies neutron-atom collisions at similar momentum transfers.
    BibTeX:
    @article{Vos2006a,
      author = {Vos, M. and Went, M.R.},
      title = {Effects of bonding on the energy distribution of electrons scattered elastically at high momentum transfer},
      journal = {Physical Review B},
      year = {2006},
      volume = {74},
      pages = {205407},
      url = {http://link.aps.org/abstract/PRB/v74/e205407}
    }
    					
    Went2006 Went, M.R. & Vos, M. High-resolution study of quasi-elastic electron scattering from a two-layer system 2006 Surface Science
    Vol. 600 (10) , pp. 2070-2078  
    article mean free paths; elemental solids; energy-loss; spectra; surface; reflection
    Abstract: In large-angle elastic scattering events of keV electrons a significant amount of momentum is transferred from the electron to a nucleus in the target. As a consequence kinetic energy is transferred from the energetic electron to the nucleus, and hence these processes can be referred to as 'quasi-elastic'. How much energy is transferred depends on the mass of the nucleus. In this paper, we present measurements from a two-layer system (a germanium layer and a carbon layer), and at high energies the quasi-elastic peaks of Ge and C are clearly resolved. It is demonstrated that the sample geometry has a huge effect on the observed relative intensities. It is shown that the intensities are influenced by the elastic scattering cross-section of the atoms in the film, film composition and selective attenuation, due to varying amount of inelastic scattering for layers of the film. However truly quantitative agreement is not obtained.
    BibTeX:
    @article{Went2006,
      author = {Went, M. R. and Vos, M.},
      title = {High-resolution study of quasi-elastic electron scattering from a two-layer system},
      journal = {Surface Science},
      year = {2006},
      volume = {600},
      number = {10},
      pages = {2070--2078},
      url = {http://dx.doi.org/10.1016/j.susc.2006.02.038}
    }
    					
    Went2006a Went, M.R.; Vos, M. & Kheifets, A.S. Elastic and inelastic scattering in electron momentum spectroscopy of amorphous Ge films 2006 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 152 (1-2) , pp. 78-86  
    article germanium
    Abstract: Electron momentum spectroscopy (an (e, 2e) experiment in the high-energy and large momentum transfer limit) is a scattering approach to the study of the electronic structure. The intensity observed in these experiment is, for an infinitely thin film, simply proportional to the spectral momentum density. For experiments using free-standing films of a more realistic thickness (100 angstrom or so), elastic and inelastic multiple scattering events are frequent and their influence on the observed intensity cannot be neglected. Here we study germanium films where the sp derived valence band can be measured simultaneously with the shallow, non-dispersing, 3d level. Somewhat surprisingly, the intensity of the 3d level, relative to that of the valence band, increases with film thickness. This effect is attributed to elastic multiple scattering. Monte Carlo simulations reproduce the changes in the observed intensity distributions with increasing film thickness.
    BibTeX:
    @article{Went2006a,
      author = {Went, M. R. and Vos, M. and Kheifets, A. S.},
      title = {Elastic and inelastic scattering in electron momentum spectroscopy of amorphous Ge films},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2006},
      volume = {152},
      number = {1-2},
      pages = {78--86},
      url = {http://dx.doi.org/10.1016/j.elspec.2006.03.005}
    }
    					
    Went2006b Went, M.R.; Vos, M. & Kheifets, A.S. Satellite structure in Auger and (e, 2e) spectra of germanium 2006 Radiation Physics and Chemistry
    Vol. 75 , pp. 1698  
    article auger;ems;satellite:germanium;
    Abstract: The interpretation of electron spectroscopy data is often complicated by the presence of satellites. These satellites are either due to different final states reached after the excitation (intrinsic satellites) or due to energy loss experienced by the escaping electron on its way out the target (extrinsic satellites). Unravelling these two contributions in an unambiguous way is difficult. In this paper we compare the intrinsic satellite structures obtained for germanium by two different high-energy spectroscopies: Auger spectroscopy of deep core levels and valence band electron momentum spectroscopy. Despite the different nature of the two probes we find a similar shape of the intrinsic satellites and comparable intensity.
    BibTeX:
    @article{Went2006b,
      author = {M.R. Went and M. Vos and A.S. Kheifets},
      title = {Satellite structure in Auger and (e, 2e) spectra of germanium},
      journal = {Radiation Physics and Chemistry},
      year = {2006},
      volume = {75},
      pages = {1698},
      url = {http://dx.doi.org/10.1016/j.radphyschem.2006.09.003}
    }
    					
    Cooper2007 Cooper, G.; Hitchcock, A.P.; Chatzidimitriou-Dreismann, C.A. & Vos, M. Electron Compton scattering from methane and methane-d4 2007 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 155 , pp. 28  
    article erbs; methane;
    Abstract: Quasi-elastic electron scattering at high momentum transfer was measured the gas phase. At high momentum transfer, two scattering peaks are observed We interpret the splitting as due to independent Compton scattering from that, at an impact energy of 2 keV and 100o scattering angle, the peaks for are split by 2.1 eV while those associated with the C and D in CD4 are split splittings are in agreement with those predicted from Rutherford scattering single atoms. The widths of the C, H and D peaks are very different, and of their momentum. The lineshapes of the H(D) peaks are in agreement space vibrational wavefunction. Detailed peak area analysis reveals anomalously for the hydrogen and deuterium peaks relative to the carbon peak ? the theoretical C:H ratio is 9.0, compared with 9.8(2) (C:H) and 9.7(2) (C:D) measured possible explanations for this discrepancy, one due to deviations of the actual the Rutherford values, the other due to short lived quantum entanglement, Rutherford scattering interpretation is compared to that for vibrational Compton- predicted by Bonham and de Souza (J. Chem. Phys, 79 (1983) 134).
    BibTeX:
    @article{Cooper2007,
      author = {G. Cooper and A.P. Hitchcock and C.A. Chatzidimitriou-Dreismann and M. Vos},
      title = {Electron Compton scattering from methane and methane-d4},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2007},
      volume = {155},
      pages = {28},
      url = {http://dx.doi.org/10.1016/j.elspec.2006.11.001}
    }
    					
    Vos2007 Vos, M. & Went, M.R. Elastic electron scattering at high momentum transfer: a possible new analytic tool 2007 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 155 , pp. 35  
    article erbs;
    Abstract: Recently it has become clear that for large-angle elastic scattering of keV electrons the energy of the scattered electrons is reduced. This energy loss depends on the mass of the atom it scattered from, as well as its momentum. Hence we can study the atomic composition of samples as well as their vibrational properties in momentum space. Here we present some examples of spectra obtained by this technique and discuss possible applications in the field of scanning electron microscopy.
    BibTeX:
    @article{Vos2007,
      author = {Vos, M and Went, M.R.},
      title = {Elastic electron scattering at high momentum transfer: a possible new analytic tool},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2007},
      volume = {155},
      pages = {35},
      url = {http://dx.doi.org/10.1016/j.elspec.2006.09.003}
    }
    					
    Vos2007a Vos, M. Wang, F. & Brunger, M.J. (Hrsg.) Electron Momentum Spectroscopy of crystals: from dream to reality 2007 Nanoscale Interactions and their applications: Essays in honour of Ian McCarthy
    Vol. -- , pp. 147-156  
    article ems; graphite;silicon;
    Abstract: The use of Electron Momentum Spectroscopy for the study of thin, single-crystal films is sketched. These films have an anisotropic electronic structure. Resolving this anisotropy in (e,2e) experiments has been a dream that has become a reality in recent years. Here I describe some results for graphite, silicon and noble metals. The experimental results are used to illustrate the concepts of Brillouin zone boundaries and Bloch functions, both central to condensed matter physics.
    BibTeX:
    @article{Vos2007a,
      author = {Vos, M.},
      title = {Electron Momentum Spectroscopy of crystals: from dream to reality},
      journal = {Nanoscale Interactions and their applications: Essays in honour of Ian McCarthy},
      publisher = {Research Signpost, Karala India},
      year = {2007},
      volume = {--},
      pages = {147--156},
      url = {http://wwwrsphysse.anu.edu.au/ vos107/Ian_Essayfinal.pdf}
    }
    					
    Vos2007b Vos, M. & Went, M.R. Experimental confirmation of the EPES sampling depth paradox for overlayer/substrate systems 2007 Surface Science
    Vol. 601 , pp. 1536  
    article erbs; carbon; gold; sampling depth;
    Abstract: Elastic peak electron spectroscopy (EPES) has been one of the main tools for obtaining the inelastic mean free path of electrons in solids. Recently it has become clear that, if this type of experiment is done using an energetic electron beam (20-40 keV) and large scattering angles, then the recoil energy of the elastic scattering event can be resolved. This recoil energy is mass dependent and this fact makes it possible to separate the elastic peak contributions due to electrons scattered from light and heavy elements. Here we use this technique to determine experimentally the sampling depth for an overlayer/substrate system. The sampling depth for a (high-Z) Au overlayer on a (low-Z) C substrate is found to be about two orders of magnitude smaller than for a C overlayer on a Au substrate, whereas the inelastic mean free path of electrons in both materials differ much less. This effect is shown to be a consequence of the peculiar definition of the sampling depth in combination with the strong Z dependence of the elastic scattering cross section. The dependence of the spectra on the electron kinetic energy and sample rotation is also dramatically different for both sample geometries.
    BibTeX:
    @article{Vos2007b,
      author = {M. Vos and M. R. Went},
      title = {Experimental confirmation of the EPES sampling depth paradox for overlayer/substrate systems},
      journal = {Surface Science},
      year = {2007},
      volume = {601},
      pages = {1536},
      url = {http://dx.doi.org/doi:10.1016/j.susc.2007.01.014}
    }
    					
    Vos2007d Vos, M. & Went, M.R. Metal interface formation studied by high-energy reflection energy loss spectroscopy and electron Rutherford backscattering 2007 Surface Science
    Vol. 601 , pp. 4862 - 4872  
    article
    Abstract: We demonstrate that high-energy, high-resolution reflection electron energy loss spectroscopy can provide unique insights into interface formation, especially for the case where an extended interface is formed. By changing the geometry and/or electron energy the electronic structure can be probed over a range of thicknesses (from 10's of Å to more than 1000 Å ). At the same time one resolves the elastically scattered electrons into different components, corresponding to scattering of atoms with different mass(so called `electron Rutherford backscattering'). Thus these high-energy REELS/elastic scattering experiments obtain information on both the electronic structure and the atomic composition of the overlayer formed.
    BibTeX:
    @article{Vos2007d,
      author = {M. Vos and M.R. Went},
      title = {Metal interface formation studied by high-energy reflection energy loss spectroscopy and electron Rutherford backscattering},
      journal = {Surface Science},
      year = {2007},
      volume = {601},
      pages = {4862 -- 4872},
      url = {http://dx.doi.org/10.1016/j.susc.2007.07.031}
    }
    					
    Went2007 Went, M.R.; Vos, M. & Elliman, R.G. Electron inelastic mean free path in solids as determined by electron Rutherford back-scattering 2007 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 156-158 , pp. 387-392  
    article erbs;carbon gold;
    Abstract: Energetic electrons scattering elastically over large angles from atoms lose energy depending on the mass of the scattering atom. If the energy of the incident electron is large enough, 10's of keV, this energy loss can be measured with high resolution electron spectrometers, allowing the separation of heavy and light elements. This technique is in many ways analogous to Rutherford back-scattering (RBS), with electrons employed as the scattering particle rather than ions. We refer to these measurements as electron Rutherford back-scattering (ERBS). We present ERBS data for a simple two layer system (gold on carbon). It is shown that this method can be used to determine the inelastic mean free path of electrons in carbon. We obtain a value of 350 §50 ºA for 40 keV electrons in amorphous carbon. A comparison of the ERBS results is made with traditional RBS results from the same ¯lm. A consistent interpretation of both measurements using calculated differential elastic cross sections was not obtained.
    BibTeX:
    @article{Went2007,
      author = {Went, M.R. and Vos, M. and Elliman, R. G.},
      title = {Electron inelastic mean free path in solids as determined by electron Rutherford back-scattering},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2007},
      volume = {156-158},
      pages = {387-392},
      url = {http://dx.doi.org/doi:10.1016/j.elspec.2006.11.041}
    }
    					
    Went2007a Went, M.R. & Vos, M. Investigation of binary compounds using electron Rutherford back scattering 2007 Applied Physics Letters
    Vol. 90 , pp. 072104  
    article erbs compounds
    Abstract: High-energy (40 keV) electrons, scattering over large angles, transfer a small fraction of their kinetic energy to the target atoms, in the same way as ions do in Rutherford back scattering (RBS) experiments. We show here that this energy transfer can be resolved and used to determine the mass of the scattering atom. In this way information on the surface composition for thicknesses of the order of 10 nm can be obtained. We refer to this new technique as `electron Rutherford back scattering' (ERBS). In addition the peak width reveal unique information about the vibrational properties (mean kinetic energy) of the scattering atoms. Here we demonstrate that that method can be used to identify a number of technological important compounds.
    BibTeX:
    @article{Went2007a,
      author = {M.R. Went and M. Vos},
      title = {Investigation of binary compounds using electron Rutherford back scattering},
      journal = {Applied Physics Letters},
      year = {2007},
      volume = {90},
      pages = {072104},
      url = {http://dx.doi.org/10.1063/1.2535986}
    }
    					
    Went2007b Went, M.R. & Vos, M. Electron Rutherford back-scattering case study: oxidation and ion implantation of aluminium foil 2007 Surface and Interface Analysis
    Vol. 39 , pp. 871 - 876  
    article
    Abstract: Electron Rutherford back scattering (ERBS) is a new spectroscopy for determining the composition of surfaces. In this work the surface sensitivity of ERBS was investigated by changing the entrance and exit angle of the electron beam while keeping the scattering angle constant. It was found that in this way the surface sensitivity of the technique can be varied considerably. We use aluminium as a test case for ERBS, as it is well studied. The technique has been used to investigate the oxide film of aluminium foil as manufactured and the native oxide (Al2O3) film formed on a clean aluminium surface exposed to air. We have also used ERBS to investigate the presence of Xe, implanted during the sputter cleaning process, at a variety of depths within an aluminium matrix.
    BibTeX:
    @article{Went2007b,
      author = {M.R. Went and M. Vos},
      title = {Electron Rutherford back-scattering case study: oxidation and ion implantation of aluminium foil},
      journal = {Surface and Interface Analysis},
      year = {2007},
      volume = {39},
      pages = {871 -- 876},
      url = {http://dx.doi.org/10.1002/sia.2603}
    }
    					
    Werner2007 Werner, W.S.M.; Went, M.R. & Vos, M. Surface Plasmon Excitation at a Au Surface by 150-40000 eV Electrons 2007 Surface Science
    Vol. 601 , pp. L109 - L113  
    article
    Abstract: Spectra of electrons with energies between 5 and 40 keV reflected from a homogeneous Au surface have been measured and analyzed to give the normalized distribution of energy losses in a single surface and volume excitation, as well as the total probability for excitation of surface plasmons. The resulting single scattering loss distributions compare excellently in (absolute units) with data from previous work taken at lower energies (150-3400 eV). An empirical relationship is derived for the total surface excitation probability as a function of the energy. For high energies the surface scattering zone represents only a small fraction of a typical electron trajectory and hence interference effects should be small at these energies. Since we find that both the energy dependence of the surface plasmon excitation probability and the shape of the single scattering loss distributions is the same at high and low electron energies, we conclude that there is no evidence for interference effects in the entire energy range studied.
    BibTeX:
    @article{Werner2007,
      author = {W.S.M. Werner and M. R. Went and M. Vos},
      title = {Surface Plasmon Excitation at a Au Surface by 150--40000 eV Electrons},
      journal = {Surface Science},
      year = {2007},
      volume = {601},
      pages = {L109 - L113},
      url = {http://dx.doi.org/doi:10.1016/j.susc.2007.06.076}
    }
    					
    Zhao2007 Zhao, Y.; Wu, Y.S.; Kong, C.; Wexler, D.; Vos, M.; Went, M.R. & Dou, S.X. Phase evolution in PLD MgB2 films during the in situ annealing process 2007 Supercond. Sci. Technol
    Vol. 20 , pp. S467-S471  
    article
    Abstract: The transformation of ZFC magnetization curves of PLD MgB_2 films annealed in situ for different dwell times and at different temperatures is studied within the context of structural analysis. The PLD films were deposited using an off-axis geometry followed by two series of annealing conditions: the dwell time series and the annealing temperature series. ZFC magnetization curves were obtained in an MPMS magnetometer from samples that had been cut into similar shapes. XRD scans on the two series of film samples show enhanced (001) and (002) MgB2 peaks till a dwell time of 9 min at 650 and a 800 C annealing temperature. TEM results show a granular transformation from an un-annealed film to a 700 ◦C 9min in situ annealed film. The possible structural development with annealing time and annealing temperature is then discussed.
    BibTeX:
    @article{Zhao2007,
      author = {Y. Zhao and Y.S. Wu and C. Kong and D. Wexler and M. Vos and M.R. Went and S. X. Dou},
      title = {Phase evolution in PLD MgB2 films during the in situ annealing process},
      journal = {Supercond. Sci. Technol},
      year = {2007},
      volume = {20},
      pages = {S467--S471},
      url = {http://dx.doi.org/doi:10.1088/0953-2048/20/11/S32}
    }
    					
    Vos2008 Vos, M. & Went, M.R. Splitting the plasmon peak in high-energy reflection electron energy loss experiments 2008 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 162 , pp. 1 - 7  
    article
    Abstract: Elastic scattering of energetic electrons over large angles (in this study 40 keV and 120degrees) implies momentum and hence energy transfer from an electron to a nucleus. Due to the large mass of the nucleus (relative to the mass of an electron) this energy transfer is small, but it was recently shown that it can be resolved in a modern spectrometer. Hence the elastic peak of an overlayer/substrate system splits into different components corresponding to atoms with dfferent mass. Here we extend this type of experiments to the plasmon part of a reflection energy loss spectroscopy (REELS) spectrum. It is shown that, for suitable systems, the plasmon peak of an overlayer/substrate system is split by the same amount as the elastic peak. This is a consequence of the fact that detection of an electron in REELS always requires a large-angle elastic scattering event. Moreover we show that the relative intensity of the plasmon components contains information on the depth distribution of the scatterers.
    BibTeX:
    @article{Vos2008,
      author = {M.  Vos and M.R.  Went},
      title = {Splitting the plasmon peak in high-energy reflection electron energy loss experiments},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2008},
      volume = {162},
      pages = {1 -- 7},
      url = {http://dx.doi.org/10.1016/j.elspec.2007.05.003}
    }
    					
    Vos2008a Vos, M. & Went, M.R. Rutherford backscattering using electrons as projectiles: underlying principles and possible applications 2008 Nuclear Instruments and Methods in Physics Research Section B
    Vol. 266 , pp. 998 -1011  
    article
    Abstract: Ion beam analysis is the method of choice to study the composition of the near surface area. Electron spectroscopy is the preferred tool to study the electronic structure. Recently it has become clear that scattering of keV electrons can be used to determine the surface composition in a way very similar to ion scattering experiments. These electron scattering experiments share much of the underlying physics of electron spectroscopy and ion scattering. In this paper we I systematically describe the similarities and differences between the electron scattering experiments and the ion beam experiments, and illustrate this description with relevant electron scattering examples.
    BibTeX:
    @article{Vos2008a,
      author = {M. Vos and M.R. Went},
      title = {Rutherford backscattering using electrons as projectiles: underlying principles and possible applications},
      journal = {Nuclear Instruments and Methods in Physics Research Section B},
      year = {2008},
      volume = {266},
      pages = {998 -1011},
      url = {http://dx.doi.org/doi:10.1016/j.nimb.2008.01.059}
    }
    					
    Vos2008b Vos, M.; Went, M.R.; Kayanuma, Y.; Tanaka, S.; Takata, Y. & Mayers, J. A comparison of recoil effects in graphite as observed by photoemission, electron scattering and neutron scattering 2008 Physical Review B
    Vol. 78 , pp. 024301  
    article
    Abstract: Recoil effects have been observed for neutron scattering, electron scattering and in photoemission. In all cases highly oriented pyrolytic graphite was used as a testing material, and dependencies of recoil effects on the crystal orientation were found, but these results have so far, not been compared. We show that the same theory can describe the results of all three experiments in a quantitative way.
    BibTeX:
    @article{Vos2008b,
      author = {M. Vos and M. R. Went and Y. Kayanuma and S. Tanaka and Y. Takata and J. Mayers},
      title = {A comparison of recoil effects in graphite as observed by photoemission, electron scattering and neutron scattering},
      journal = {Physical Review B},
      year = {2008},
      volume = {78},
      pages = {024301},
      url = {http://link.aps.org/abstract/PRB/v78/e024301}
    }
    					
    Vos2008c Vos, M.; Went, M.R.; Cooper, G. & Chatzidimitriou-Dreismann, C.A. Elastic electron scattering from methane at high momentum transfer 2008 J. Phys. B.
    Vol. 41 , pp. 135204-135213  
    article
    Abstract: We describe elastic electron scattering data at high momentum transfer (between ≈20 and ≈40 a.u.) from methane and Xe. Under these conditions there is a significant recoil energy transferred to the target and electrons scattered elastically from methane are separated into two peaks: one due to electrons scattered from carbon, and one due to electrons scattered from hydrogen. The separation of these peaks is within a few % identical to what is expected for scattering from isolated C and H atoms. The peak, due to electrons scattered from C, is again shifted compared to the peak of electrons scattered from Xe. The Xe, C and H peak all have clearly different width. The C and H peak areas are compared. Their relative intensity shows no substantial deviation (<10 from what is expected based on either simple Rutherford cross sections, or state-of-the-art elastic scattering calculations. The latter observation is in strong contrast to electron scattering results from gaseous equimolar H2-D2 mixture and from electron and neutron scattering results from polymers at similar momentum transfer.
    BibTeX:
    @article{Vos2008c,
      author = {M. Vos and M.R. Went and G. Cooper and C.A. Chatzidimitriou-Dreismann},
      title = {Elastic electron scattering from methane at high momentum transfer},
      journal = {J. Phys. B.},
      year = {2008},
      volume = {41},
      pages = {135204-135213},
      url = {http://www.iop.org/EJ/abstract/0953-4075/41/13/135204/}
    }
    					
    Went2008 Went, M.R.; Vos, M. & Werner, W.S.M. Extracting the Ag surface and volume loss functions from reflection electron energy loss spectra 2008 Surface Science
    Vol. 602 , pp. 2069 -2077  
    article
    Abstract: The measurements of energy loss distributions obtained in electron scattering experiments at high momentum transfer are presented for Xe, Ar and methane. The spectra show a large variety of intensity distributions, clearly different from those obtained in measurements at the dipole limit. The fraction of the intensity present in the energy loss distribution compared to the elastic peak is significant, but is in line with the reduction of the elastic cross section due to absorption. It is argued that, if similar effects are present in the condensed phase, they should be dealt with in any quantitative analysis of electron transport in matter, as is often done using Monte Carlo simulations. This argument is worked out in some detail for Reflection Electron Energy Loss Spectroscopy.
    BibTeX:
    @article{Went2008,
      author = {M. R. Went and M. Vos and W.S.M. Werner},
      title = {Extracting the Ag surface and volume loss functions from reflection electron energy loss spectra},
      journal = {Surface Science},
      year = {2008},
      volume = {602},
      pages = {2069 --2077},
      url = {http://dx.doi.org/10.1016/j.susc.2008.04.011}
    }
    					
    Werner2008 Werner, W.S.M.; Went, M.R.; Vos, M.; Glantschnig, K. & Ambrosch-Draxl, C. Measurement and Density Functional Calculations of Optical Constants of Ag and Au from Infrared to VUV Wavelengths. 2008 Physical Review B
    Vol. 77 , pp. 161404  
    article
    Abstract: The dielectric function of Ag and Au for wavelengths ranging from the infrared to the vacuum ultraviolet regime was measured with reflection electron energy-loss spectroscopy (REELS). The spectra are compared to density functional theory (DFT) calculations and to experimental optical data available in the literature since about three decades ago. The REELS and DFT results exhibit good consistency, while the earlier optical data significantly deviate. The results demonstrate that REELS and DFT are powerful tools for the study of the electromagnetic response of surfaces.
    BibTeX:
    @article{Werner2008,
      author = {W.S.M. Werner and M. R. Went and M. Vos, and K. Glantschnig and C. Ambrosch-Draxl},
      title = {Measurement and Density Functional Calculations of Optical Constants of Ag and Au from Infrared to VUV Wavelengths.},
      journal = {Physical Review B},
      year = {2008},
      volume = {77},
      pages = {161404},
      url = {http://link.aps.org/abstract/PRB/v77/e161404}
    }
    					
    Vos2009 Vos, M. & Went, M.R. Elastic electron scattering from hydrogen molecules at high momentum transfer 2009 Journal of Physics B: Atomic, Molecular and Optical Physics
    Vol. 42 , pp. 065204  
    article
    Abstract: In high-momentum transfer electron scattering experiments the `elastic signal' is separated in different components, depending on the mass of the scatterer due to the recoil effect. Here we compare the peak positions and shapes obtained from H_2, D_2 and HD with theory developed for neutron scattering experiments at similar momentum transfer. The hydrogen peak width increases with increasing momentum transfer. The observed width is in line with the vibrational properties of H_2. The line shape of the elastic peak is also studied for HD and D_2 molecules. The H peak in HD is broader than the H peak of H_2, and the D peak of D_2 is broader than that of the D peak of HD. We also investigate elastic scattering at high momentum transfer of gas mixtures containing hydrogen and either heavy (Xe) or light (He) noble gases. Changing the energy of the incoming beam changes for the Xe/H_2 gas mixture the ratio of the Xe and H_2 signal in a dramatic way, but for the He/H_2 mixture the intensity ratio is constant. The energy-dependence of the observed intensity ratio is in both cases accurately described by `standard' differential elastic cross section calculations. Results are discussed in the context of a recent report of anomalies in electron scattering results of H_2 under similar experimental conditions and anomalous neutron scattering results of H_2, D_2 mixtures and HD. An in-depth look at the peak shape of hydrogen reveals deviations from a simple Gaussian line shape which are interpreted to be, at least in part, a consequence of the bonding of the nucleus to a molecule.
    BibTeX:
    @article{Vos2009,
      author = {M Vos and M R Went},
      title = {Elastic electron scattering from hydrogen molecules at high momentum transfer},
      journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      year = {2009},
      volume = {42},
      pages = {065204},
      url = {http://stacks.iop.org/0953-4075/42/065204}
    }
    					
    Vos2009a Vos, M.; Went, M.R. & Weigold, E. Electron Spectroscopy using Two-dimensional Electron Detection based on a CCD camera in the pulse counting mode. 2009 Review of Scientific Instruments
    Vol. 80 , pp. 063302  
    article
    Abstract: A brief description is given of an economical implementation of the read out of a two-dimensional detector in an electron spectrometer by a charge coupled device camera, using a pulse counting mode. Count rates up to 10 kHz can be handled in this way. A comparison with results obtained using a resistive anode detector is given for the case of electron scattering from Xe atoms. Good agreement was obtained between both detection techniques, establishing the validity of the method described here.
    BibTeX:
    @article{Vos2009a,
      author = {M. Vos and M.R. Went and E. Weigold},
      title = {Electron Spectroscopy using Two-dimensional Electron Detection based on a CCD camera in the pulse counting mode.},
      journal = {Review of Scientific Instruments},
      year = {2009},
      volume = {80},
      pages = {063302},
      url = {http://link.aip.org/link/?RSINAK/80/063302/1}
    }
    					
    Vos2009b Vos, M.; Went, M.R. & Winkelmann, A. Quantitative measurements of Kikuchi bands in diffraction patterns of backscattered electrons using an electrostatic analyzer 2009 Ultramicroscopy
    Vol. 109 , pp. 1211  
    article
    Abstract: Diffraction patterns of backscattered electrons can provide important crystallographic information with high spatial resolution. Recently, the dynamical theory of electron diffraction was applied to reproduce in great detail backscattering patterns observed in the scanning electron microscope (SEM). However, a fully quantitative comparison of theory and experiment requires angle-resolved measurements of the intensity and the energy of the backscattered electrons, which is difficult to realize in an SEM. This paper determines diffraction patterns of backscattered electrons using an electrostatic analyzer, operating at energies up to 40 keV with sub-eV energy resolution. Measurements are done for different measurement geometries, and incoming energies. Generally a good agreement is found between theory and experiment. This spectrometer also allows us to test the influence of the energy loss of the detected electron on the backscattered electron diffraction pattern. It is found that the amplitude of the intensity variation decreases only slowly with increasing energy loss from 0 to 60eV.
    BibTeX:
    @article{Vos2009b,
      author = {M. Vos and M.R. Went and A. Winkelmann},
      title = {Quantitative measurements of Kikuchi bands in diffraction patterns of backscattered electrons using an electrostatic analyzer},
      journal = {Ultramicroscopy},
      year = {2009},
      volume = {109},
      pages = {1211},
      url = {http://dx.doi.org/10.1016/j.ultramic.2009.05.004}
    }
    					
    Went2009 Went, M.R. & Vos, M. The role of absorption in large-angle elastic scattering 2009 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 169 , pp. 35 -40  
    article
    Abstract: The measurements of energy loss distributions obtained in electron scattering experiments at high momentum transfer are presented for Xe, Ar and methane. The spectra show a large variety of intensity distributions, clearly different from those obtained in measurements at the dipole limit. The fraction of the intensity present in the energy loss distribution compared to the elastic peak is significant, but is in line with the reduction of the elastic cross section due to absorption. It is argued that, if similar effects are present in the condensed phase, they should be dealt with in any quantitative analysis of electron transport in matter, as is often done using Monte Carlo simulations. This argument is worked out in some detail for Reflection Electron Energy Loss Spectroscopy.
    BibTeX:
    @article{Went2009,
      author = {M.R. Went and M. Vos},
      title = {The role of absorption in large-angle elastic scattering},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2009},
      volume = {169},
      pages = {35 --40},
      url = {http://dx.doi.org/10.1016/j.elspec.2008.10.001}
    }
    					
    Afanas'ev2010 Afanas'ev, V.P.; Afanas'ev, M.V.; Lubenchenko, A.V.; Batrakov, A.A.; Efremenko, D.S. & Vos, M. Influence of multiple elastic scattering on the shape of the elastically-scattered electron peak 2010 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 177 , pp. 35-41  
    article multiple scattering
    Abstract: The influence of multiple elastic scattering on the shape of the energy distribution of elastically scattered electrons is investigated. The energy of the maximum intensity of the detected electrons differs from the probe electron beam energy due to the elastic energy loss. The experimentally observed spectrum is adequately described by a Gaussian distribution with a maximum at the elastic energy loss value. In this paper the peak-broadening mechanisms due to energy analyzer spread function, probe beam energy distribution and atomic vibration-induced broadening are considered to be independent and of random nature. Analysis of multiple elastic scattering shows some mechanisms leading to the broadening and a shift of the elastic scattering electron energy spectrum from the value defined by single elastic scattering at the certain angle. It is revealed that the magnitude of this shift and the width of energy distrubution is determined by ratio (l_in = l_tr), where l_in is inelastic mean free pass, ltr is the transport length. Monte Carlo computation results for elastic energy losses of electrons moving in a solid with stationary atoms are presented as well. The possibility of observing experimentally the elastic peak broadening and shift due to multiple elastic scattering is discussed.
    BibTeX:
    @article{Afanas'ev2010,
      author = {V.P. Afanas'ev and M.V. Afanas'ev and A.V. Lubenchenko and A.A. Batrakov and D.S. Efremenko and M. Vos},
      title = {Influence of multiple elastic scattering on the shape of the elastically-scattered electron peak},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2010},
      volume = {177},
      pages = {35--41},
      url = {http://www.sciencedirect.com/science/article/B6TGC-4Y65S9P-1/2/6f0431ff614bd76bfe7825e983da6ab9},
      doi = {https://doi.org/10.1016/j.elspec.2010.01.002}
    }
    					
    Bradley2010 Bradley, J.A.; Seidler, G.T.; Cooper, G.; Vos, M.; Hitchcock, A.P.; Sorini, A.P.; Schlimmer, C. & Nagle, K.P. Comparative Study of the Valence Electronic Excitations of N2 by Inelastic X-Ray and Electron Scattering 2010 Phys. Rev. Lett.
    Vol. 105 (5) , pp. 053202  
    article
    Abstract: Bound-state, valence electronic excitation spectra of N2 are probed by nonresonant inelastic x-ray and electron scattering. Within usual theoretical treatments, dynamical structure factors derived from the two probes should be identical. However, we find strong disagreements outside the dipole scattering limit, even at high probe energies. This suggests an unexpectedly important contribution from intramolecular multiple scattering of the probe electron from core electrons or the nucleus. These effects should grow progressively stronger as the atomic number of the target species increases.
    BibTeX:
    @article{Bradley2010,
      author = {Bradley, J. A. and Seidler, G. T. and Cooper, G. and Vos, M. and Hitchcock, A. P. and Sorini, A. P. and Schlimmer, C. and Nagle, K. P.},
      title = {Comparative Study of the Valence Electronic Excitations of N2 by Inelastic X-Ray and Electron Scattering},
      journal = {Phys. Rev. Lett.},
      publisher = {American Physical Society},
      year = {2010},
      volume = {105},
      number = {5},
      pages = {053202},
      url = {http://link.aps.org/doi/10.1103/PhysRevLett.105.053202}
    }
    					
    Vos2010 Vos, M. Electron scattering at high momentum transfer from methane: Analysis of line shapes 2010 Journal of Chemical Physics
    Vol. 132 , pp. 074306  
    article
    Abstract: The measurement of the energy distribution of keV electrons backscattered elastically from molecules reveals one or more peaks. These peaks are at nonzero energy loss and have an intrinsic width. The usual interpretation of these measurements is attractively simple and assumes billiard-ball-type collisions between the electron and a specific atom in the molecule, and the scattering atom is assumed to behave as a free particle. The peak position is then related to the mass of the scattering atom, and its width is a Compton profile of the momentum distribution of this atom in the molecule. Here we explore the limits of the validity of this picture for the case of electrons scattering from methane. The biggest discrepancy is found for electrons scattering from carbon. For electrons scattering from hydrogen the effects are substantial at relatively low incoming energies and appear to decrease with increasing momentum transfer. The discrepancy is analyzed in terms of the force the atom experiences near the equilibrium position.
    BibTeX:
    @article{Vos2010,
      author = {M. Vos},
      title = {Electron scattering at high momentum transfer from methane: Analysis of line shapes},
      journal = {Journal of Chemical Physics},
      year = {2010},
      volume = {132},
      pages = {074306},
      url = {http://jcp.aip.org/jcpsa6/v132/i7/p074306_s1}
    }
    					
    Vos2010a Vos, M.; Aizel, K. & Winkelmann, A. Experimental Observation of the Strong Influence of Crystal Orientation on Electron Rutherford Backscattering Spectra 2010 Surface Science
    Vol. 604 , pp. 893-897  
    article
    Abstract: In Electron Rutherford Backscattering Spectroscopy (ERBS) energetic electrons (in our case up to 40 keV) impinge on a target and one measures the energy of elastically scattered electrons. This energy depends on the mass of the scattering atom, due to the recoil effect. This technique thus provides information about the sample composition. For single crystals the interaction of the projectile electron with the crystal potential modifies the angular intensity distribution of the scattered electrons. This leads, for example, to the well-known Kikuchi patterns. Here we investigate if such modified angular distribution has any influence on the intensity ratio of the observed elastic peaks in ERBS. Dramatic effects are found. Implications of these observations for quantitative surface analysis using energetic electrons are discussed.
    BibTeX:
    @article{Vos2010a,
      author = {M. Vos and K. Aizel and A. Winkelmann},
      title = {Experimental Observation of the Strong Influence of Crystal Orientation on Electron Rutherford Backscattering Spectra},
      journal = {Surface Science},
      year = {2010},
      volume = {604},
      pages = {893--897},
      url = {http://dx.doi.org/10.1016/j.susc.2010.02.016}
    }
    					
    Vos2010b Vos, M. Electron scattering from Xe: the relation between the differential elastic cross section and shape and intensity of the energy loss spectra 2010 Journal of Physics B: Atomic, Molecular and Optical Physics
    Vol. 43 , pp. 215201  
    article
    Abstract: The measurement of the energy loss spectra of energetic electrons scattered from Xe over large angles is reported. The incoming energy was chosen between 600 eV and 1550 eV. The calculated Xe elastic scattering cross section has a sharp minimum for 750 eV electrons near 135degree. This minimum is confirmed by studying a Xe-H_2 mixture and separating their elastic peak based on the recoil effect. The energy loss part of the Xe spectra is rich in structure. Surprisingly the shape and intensity (relative to the elastic peak) changes dramatically if one approaches the scattering conditions for which the elastic cross section has a minimum. These observations are rationalized by describing the inelastic intensity semi-classically: as a consequence of a two-step process occurring at the same atom involving scattering from the nucleus and an electronic excitation. The change in shape of the loss spectra is attributed to a large increase in relative intensity of the dipole-forbidden transitions near sharp minima in the elastic cross section.
    BibTeX:
    @article{Vos2010b,
      author = {M. Vos},
      title = {Electron scattering from Xe: the relation between the differential elastic cross section and shape and intensity of the energy loss spectra},
      journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      year = {2010},
      volume = {43},
      pages = {215201},
      url = {stacks.iop.org/JPhysB/43/215201}
    }
    					
    Winkelmann2010 Winkelmann, A.; Aizel, K. & Vos, M. Electron energy loss and diffraction of backscattered electrons from Silicon 2010 New Journal of Physics
    Vol. 12 , pp. 053001  
    article
    Abstract: Electrons backscattered from crystals can show Kikuchi patterns: variations in intensity for different outgoing directions due to diffraction by the lattice. Here we measure these effects as a function of their energy loss for 30keV electrons backscattered from silicon. The change in diffraction contrast with energy loss depends strongly on the scattering geometry. At steep incidence on the sample, diffraction contrast in the observed Kikuchi bands decreases rapidly with energy loss. For an energy loss larger than about 150eV the contrast is more than 5 times less than the contrast due to electrons near zero energy loss. However, for grazing incidence angles, maximum Kikuchi band contrast is observed for electrons with an energy loss near 60eV, where the contrast is more than 2.5× larger than near zero energy loss. In addition, in this grazing incidence geometry, the Kikuchi diffraction effects stay significant even for electrons which have lost hundreds of eV. For the maximum measured energy loss of 440eV, the electrons still show a contrast that is 1.5× larger than that of the electrons near zero energy loss. These geometry-dependent observations of Kikuchi band diffraction contrast are interpreted based on the elastic and inelastic scattering properties of electrons and dynamical diffraction simulations.
    BibTeX:
    @article{Winkelmann2010,
      author = {A. Winkelmann and K. Aizel and M. Vos},
      title = {Electron energy loss and diffraction of backscattered electrons from Silicon},
      journal = {New Journal of Physics},
      year = {2010},
      volume = {12},
      pages = {053001},
      url = {http://stacks.iop.org/1367-2630/12/053001}
    }
    					
    Vos2011 Vos, M.; McEachran, R.P.; Cooper, G. & Hitchcock, A.P. Understanding energy loss in large-angle scattering of keV electrons from Ar and Ne 2011 Phys. Rev. A
    Vol. 83 (2) , pp. 022707  
    article
    Abstract: We present measurements of the spectra of electrons with energy between 0.6 and 2.25 keV elastically and inelastically scattered from Ar and Ne over large angles (from 3ˆ to 135ˆ). The intensity of the first loss feature [np→(n+1)s], relative to that of the elastic peak, was determined and compared with the results of relativistic distorted-wave calculations (for the energy loss part) and a relativistic optical potential method (for the elastic peak). Good agreement was found. The distorted-wave calculations are compared with first Born calculations. At small angles, both theories coincide and estimates of the optical oscillator strength are obtained. However, at large angles, the first Born approximation predicts negligible intensity, in strong contrast to the distorted-wave theory and the experimental data. The implications of these results for the interpretation of measurements of the generalized oscillator strength are discussed.
    BibTeX:
    @article{Vos2011,
      author = {Vos, M. and McEachran, R. P. and Cooper, G. and Hitchcock, A. P.},
      title = {Understanding energy loss in large-angle scattering of keV electrons from Ar and Ne},
      journal = {Phys. Rev. A},
      year = {2011},
      volume = {83},
      number = {2},
      pages = {022707},
      url = {http://link.aps.org/doi/10.1103/PhysRevA.83.022707}
    }
    					
    Vos2011a Vos, M.; Moreh, R.M. & Tőkési, K. The use of electron scattering for studying atomic momentum distributions: the case of graphite and diamond 2011 J. Chem. Phys.
    Vol. 135 , pp. 024504  
    article
    Abstract: The momentum distributions of C atoms in polycrystalline diamond (produced by chemical vapor deposition (CVD)) and in highly oriented pyrolitic graphite (HOPG) are studied by scattering of 40 keV electrons at 135degree . By measuring the Doppler broadening of the energy of the elastically scattered electrons, we resolve a Compton profile of the motion of the C atoms. The aim of the present work is to resolve long-standing disagreements between the calculated kinetic energies of carbon atoms in HOPG and in diamond films and the measured ones, obtained both by neutron Compton scattering (NCS) and by nuclear resonance photon scattering (NRPS). The anisotropy of the momentum distribution in HOPG was measured by rotating the HOPG sample relative to the electron beam. The obtained kinetic energies for the motion component along, and perpendicular to, the graphite planes were somewhat higher that those obtained from the most recent NCS data of HOPG. Monte Carlo Simulations indicate that multiple scattering adds about 2% to the obtained kinetic energies. The presence of different isotopes in carbon affects the measurement at a 1% level. After correcting for these contributions the kinetic energies are 3-6% larger than the most recent NCS results for HOPG, but 15- 25% smaller than the NRPS results. For diamond, the corrected directional-averaged kinetic energy is ≈ 6% larger than the calculated value. This compares favorably to the ≈ 25% discrepancy between theory and both the NCS and NRPS results for diamond.
    BibTeX:
    @article{Vos2011a,
      author = {M. Vos and R.M. Moreh and K. Tőkési},
      title = {The use of electron scattering for studying atomic momentum distributions: the case of graphite and diamond},
      journal = {J. Chem. Phys.},
      year = {2011},
      volume = {135},
      pages = {024504},
      url = {http://link.aip.org/link/doi/10.1063/1.3607993},
      doi = {https://doi.org/10.1063/1.3607993}
    }
    					
    Winkelmann2011 Winkelmann, A. & Vos, M. Site-Specific Recoil Diffraction of Backscattered Electrons in Crystals 2011 Phys. Rev. Lett.
    Vol. 106 , pp. 085503  
    article
    Abstract: A novel diffraction effect in high-energy electron backscattering is demonstrated: the formation of element-specific diffraction patterns via nuclear recoil. For sapphire (Al2O3), the difference in recoil energy allows us to determine if an electron scattered from aluminum or from oxygen. The angular electron distribution obtained in such measurements is a strong function of the recoiling lattice site. These element-specific recoil diffraction features are explained using the dynamical theory of electron diffraction. Our observations open up new possibilities for local, element-resolved crystallographic analysis using quasielastically backscattered electrons in scanning electron microscopy.
    BibTeX:
    @article{Winkelmann2011,
      author = {Winkelmann, Aimo and Vos, Maarten},
      title = {Site-Specific Recoil Diffraction of Backscattered Electrons in Crystals},
      journal = {Phys. Rev. Lett.},
      year = {2011},
      volume = {106},
      pages = {085503},
      url = {doi:10.1103/PhysRevLett.106.085503}
    }
    					
    McEachran2012 McEachran, R.P. & Vos, M. Large-angle scattering of energetic electrons from Xe: A combined theoretical and experimental approach 2012 Phys. Rev. A
    Vol. 85 , pp. 032703  
    article
    Abstract: We study the inelastic excitations of Xe for electrons with relatively high energies (500 or 750 eV) scattered over large angles, both experimentally and theoretically. In particular, we focus on the shape and intensity of the spectra of inelastically scattered electrons at the sharp dip in the elastic cross section near 135 degree at 750 eV. Under these conditions, the first Born approximation predicts virtually zero intensity. However, in reality, measurable intensity is observed. Calculations carried out using the relativistic distorted-wave method describe the measurements reasonably well. A comparison is made between the calculations and previously published high-resolution studies. Overall agreement is quite good, especially for the lowest-energy excitations, but substantial differences are found for certain higher levels. The theory reproduces quite well the variations in intensity of the inelastic excitations for measurements near the dip in the elastic-scattering cross section, somewhat surprisingly, as the theories for elastic scattering and inelastic scattering are developed along completely different lines.
    BibTeX:
    @article{McEachran2012,
      author = {McEachran, R. P. and Vos, M.},
      title = {Large-angle scattering of energetic electrons from Xe: A combined theoretical and experimental approach},
      journal = {Phys. Rev. A},
      year = {2012},
      volume = {85},
      pages = {032703},
      url = {http://link.aps.org/doi/10.1103/PhysRevA.85.032703},
      doi = {https://doi.org/10.1103/PhysRevA.85.032703}
    }
    					
    Grande2013 Grande, P.L.; Vos, M.; Venkatachalam, D.K.; Nandi, S.K. & Elliman, R.G. Determination of thickness and composition of high-k dielectrics using high-energy electrons 2013 Applied Physics Letters
    Vol. 103 , pp. 071911  
    article
    Abstract: We demonstrate the application of high-energy elastic electron backscattering to the analysis of thin (2-20nm) HfO2 overlayers on oxidized Si substrates. The film composition and thickness are determined directly from elastic scattering peaks characteristic of each element. The stoichiometry of the films is determined with an accuracy of 5-10%. The experimental results are corroborated by Medium Energy Ions Scattering (MEIS) and RBS measurements, and clearly demonstrate the efficiency of the technique for thin-film analysis. Significantly, the presented technique opens new possibilities for nm depth profiling with high spatial resolution in scanning electron microscopes.
    BibTeX:
    @article{Grande2013,
      author = {P.L. Grande and M. Vos and D.K. Venkatachalam and S.K. Nandi and R.G. Elliman},
      title = {Determination of thickness and composition of high-k dielectrics using high-energy electrons},
      journal = {Applied Physics Letters},
      year = {2013},
      volume = {103},
      pages = {071911},
      url = {http://dx.doi.org/10.1063/1.4818637}
    }
    					
    Grande2013a Grande, P.L. & Vos, M. Exploring the Barkas effect with keV electron scattering 2013 Phys. Rev. A
    Vol. 88 , pp. 052901  
    article
    Abstract: The energy loss of fast ions at close collision is mainly due to electron-ion collisions. The electrons are approximately stationary and they collide with a fast moving ion. Here we study the same collision experimentally, in a reference system where the ions (or atoms) are stationary and interacting with keV electrons. Scattering cross sections under these conditions deviate from Rutherford, and we link these deviations, at higher energies, to the Z^3 contributions to the electronic stopping and the related Barkas effect and, at lower energies, also to quantum interference. The present measurements are well described by partial wave calculations of the elastic cross-section of electrons scattering from atoms. Encouraged by this agreement we use these calculations to estimate the Barkas factor for all elements and many energies. A universal curve for the Barkas factor due to close collisions is obtained for neutral projectiles and similar curves with smaller magnitude are found for ions.
    BibTeX:
    @article{Grande2013a,
      author = {P.L. Grande and M. Vos},
      title = {Exploring the Barkas effect with keV electron scattering},
      journal = {Phys. Rev. A},
      year = {2013},
      volume = {88},
      pages = {052901},
      url = {http://pra.aps.org/abstract/PRA/v88/i5/e052901}
    }
    					
    McEachran2013 McEachran, R.P.; Vos, M. & Zhu, L.F. Fast electron scattering from Ne: a comparison of distorted wave theory with experiment 2013 Phys. Rev. A
    Vol. 87 , pp. 052703  
    article
    Abstract: We compare electron scattering data from Ne with first Born and distorted wave calculations in an energy range between 300 and 2500 eV and for scattering angles up to 135 degrees and for energy losses up to the ionization energy. At small angles the distorted wave calculations and first Born calculations are in good agreement but at large momentum transfer the intensity predicted by the first Born theory drops off much faster than the experiment and distorted wave calculations. The present distorted wave calculations reproduce most of the experimental observations quite well, except for monopole transitions and near the minima in dipole-allowed s to p transitions. The first Born approximation fails completely at larger momentum transfer
    BibTeX:
    @article{McEachran2013,
      author = {R.P. McEachran and M. Vos and L.F. Zhu},
      title = {Fast electron scattering from Ne: a comparison of distorted wave theory with experiment},
      journal = {Phys. Rev. A},
      year = {2013},
      volume = {87},
      pages = {052703},
      url = {http://link.aps.org/doi/10.1103/PhysRevA.87.052703},
      doi = {https://doi.org/10.1103/PhysRevA.87.052703}
    }
    					
    Vos2013 Vos, M.; Weigold, E. & Moreh, R. Elastic electron scattering from water vapor and ice at high momentum transfer 2013 Journal of Chemical Physics
    Vol. 138 , pp. 044307  
    article
    Abstract: We compare the area, peak separation and width of the H and O elastic peak for light and heavy water, as observed in spectra of keV electrons scattered over large angles. Peak separation is well reproduced by the theory, but the O:H area ratio is somewhat larger than expected and is equal to the O:D area ratio. Thus no anomalous scattering from H was observed. Only minor differences are observed for scattering from a gaseous or a solid target. The extracted mean kinetic energy of H and D agreed within 5% with the calculated ones for ice. For the more difficult vapor measurements agreement was on a 12% level. A preliminary attempt to extract the O kinetic energy in ice agreed within 10% with the calculated values.
    BibTeX:
    @article{Vos2013,
      author = {M. Vos and E. Weigold and R. Moreh},
      title = {Elastic electron scattering from water vapor and ice at high momentum transfer},
      journal = {Journal of Chemical Physics},
      year = {2013},
      volume = {138},
      pages = {044307},
      url = {http://dx.doi.org/10.1063/1.4775810},
      doi = {https://doi.org/10.1063/1.4775810}
    }
    					
    Vos2013a Vos, M.; Tokesi, K. & Benko, I. The potential of materials analysis by electron Rutherford backscattering as illustrated by a case study of mouse bones and related compounds 2013 Microscopy and Microanalysis
    Vol. 19 , pp. 576  
    article
    Abstract: Electron Rutherford backscattering (ERBS) is a new technique that could be developed into a tool of materials analysis. Here we try to establish a method- ology for the use of ERBS for materials analysis of more complex samples using bone minerals as a test case. For this purpose we studied also several reference samples containing Ca: calcium carbonate, hydroxyapatite as well as mouse bone powder itself. A very good understanding of the spectra of calcium carbonate and hydroxyapatite was obtained. Quantitative interpretation of the bone spectrum itself is more challenging. A good t of these spectra is only obtained with the same peak widths as used for the hydroxyapatite sample, if one allows for the presence of impurity atoms with a mass close to that of Na and Mg. Our con clusion is that a meaningful interpretation of spectra of more complex samples in terms of composition is indeed possible, but only if the widths of the peaks contributing to the spectra are known. Knowledge of the peak widths can be either developed by the study of reference samples (as was done here) or potentially they can be derived from theory.
    BibTeX:
    @article{Vos2013a,
      author = {M. Vos and K. Tokesi and I. Benko},
      title = {The potential of materials analysis by electron Rutherford backscattering as illustrated by a case study of mouse bones and related compounds},
      journal = {Microscopy and Microanalysis},
      year = {2013},
      volume = {19},
      pages = {576},
      url = {http://dx.doi.org/10.1017/S143192761300041X},
      doi = {https://doi.org/10.1017/S143192761300041X}
    }
    					
    Vos2013b Vos, M.; McEachran, R.; Weigold, E. & Bonham, R.A. Elastic electron scattering cross sections at high momentum transfer 2013 Nuclear Instruments & Methods B
    Vol. 300 , pp. 62-67  
    article
    Abstract: The elastic scattering cross section of keV electrons over large angles (>90) is discussed. A comparison is made of the Rutherford cross section, the cross section obtained in the first Born approximation and that obtained by a partial wave calculation. The last approach differs significantly from the first two. For compounds, the recoil energy makes it possible to distinguish experimentally from which atom the electron has scattered. We compare the elastic peak ratio of H and O in water at several keV and for Hf and O in HfO2 at 20–40 keV with the calculated ratios. Reasonable (but not perfect) agreement is obtained between the experiment and theory for the partial wave calculations.
    BibTeX:
    @article{Vos2013b,
      author = {M. Vos and R.P. McEachran, and E. Weigold and R.A. Bonham},
      title = {Elastic electron scattering cross sections at high momentum transfer},
      journal = {Nuclear Instruments & Methods B},
      year = {2013},
      volume = {300},
      pages = {62--67},
      url = {http://dx.doi.org/10.1016/j.nimb.2013.01.043},
      doi = {https://doi.org/10.1016/j.nimb.2013.01.043}
    }
    					
    Vos2013c Vos, M.; Grande, P.L.; Nandi., S.K.; Venkatchalam, D.K. & Elliman, R. High-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices 2013 Journal of Applied Physics
    Vol. 114 , pp. 073508  
    article
    Abstract: High-energy electron scattering is used to investigate Ta lms implanted with 10 keV O ions. These lms are of interest as they have been used successfully for the fabrication of memristors. High-energy electron scattering is used with incoming electron energies ranging from 5 to 40 keV. The inelastic mean free path, and hence the probing depth, is at these energies of the same order as the range of the implanted ions. At the same time, we can distinguish the mass of the atom that scattered the electron elastically, due to the dependence of the recoil energy on the mass of the scatterer. This allows us to determine quantitatively the atomic composition near the surface from the signal of electrons that have scattered elastically but not inelastically. Electrons that have scattered inelastically as well as elastically provide us with information on the possible electronic excitations. Their signal is used to monitor the presence of the Ta2O5 phase near the surface (characterised by a signi cant band gap of ≃ 4.5 eV), and estimate at what depth below the surface pure Ta metal is present. In this way we obtain a fairly detailed picture of the elemental composition and electronic properties of these lms.
    BibTeX:
    @article{Vos2013c,
      author = {M. Vos and P.L. Grande and S.K. Nandi. and D.K. Venkatchalam and R. Elliman},
      title = {High-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices},
      journal = {Journal of Applied Physics},
      year = {2013},
      volume = {114},
      pages = {073508},
      url = {http://dx.doi.org/10.1063/1.4818524}
    }
    					
    Vos2013d Vos, M. Extracting detailed information from reflection electron energy loss spectra 2013 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 191 , pp. 65  
    article
    Abstract: We use REELS (reflection electron energy loss spectroscopy) measurements at relatively large energies (up to 40 keV) and good energy resolution (0.3 eV) to extract the bulk and surface loss function for Au, Mo and Ta. For these cases there are small, but significant deviations between the electron-based estimates of the dielectric function as published by Werner et al (J. Phys. Chem. Ref. Data 38 1013 (2009)), and the corresponding photon absorption/reflection based estimates. The present, higher-resolution electron-based measurements reveal more of the fine structure in the surface and bulk loss function, visible previously only in the photon-derived estimates. Thus we demonstrate that it is indeed possible to resolve these fine details of the surface and bulk loss function with REELS underlining its potential for extracting information on the dielectric function of materials.
    BibTeX:
    @article{Vos2013d,
      author = {M. Vos},
      title = {Extracting detailed information from reflection electron energy loss spectra},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2013},
      volume = {191},
      pages = {65},
      url = {http://dx.doi.org/10.1016/j.elspec.2013.10.007}
    }
    					
    Winkelmann2013 Winkelmann, A. & Vos, M. The role of localized recoil in the formation of Kikuchi patterns 2013 Ultramicroscopy
    Vol. 125 , pp. 66-71  
    article
    Abstract: In electron scattering from crystals, diffraction spots are replaced by Kikuchi patterns at highomentum transfer. Kikuchi pattern formation is based on the concept of effective incoherent electron sources (or detectors) inside a crystal. The resulting incoherence is a consequence of energy transfer connected with the momentum transfer in large-angle scattering events. We identify atomic recoil as a key incoherent process giving rise to electron Kikuchi patterns in the scope of the ‘‘channeling-in and channeling-out’’ model of electron backscatter diffraction (EBSD) and electron channeling patterns (ECP) in the scanning electron microscope (SEM). Using model calculations, we explore the characteristic role of the localization of the incoherent scattering event at specific places within the unit cell. In this way, we explain why sometimes inelastic losses do cause Kikuchi-type contrast, and sometimes inelastic losses result in the disappearance of this contrast in the SEM.
    BibTeX:
    @article{Winkelmann2013,
      author = {A. Winkelmann and M. Vos},
      title = {The role of localized recoil in the formation of Kikuchi patterns},
      journal = {Ultramicroscopy},
      year = {2013},
      volume = {125},
      pages = {66--71},
      url = {http://dx.doi.org/10.1016/j.ultramic.2012.11.001},
      doi = {https://doi.org/10.1016/j.ultramic.2012.11.001}
    }
    					
    Vos2014 Vos, M.; Grande, P.L.; Venkatachalam, D.K.; Nandi, S.K. & Elliman, R.G. Oxygen self-diffusion in HfO_2 studied by electron spectroscopy 2014 Phys. Rev. Lett.
    Vol. 112 , pp. 175901  
    article
    Abstract: High-resolution measurement of the energy of electrons backscattered from oxygen atoms makes it possible to distinguish between 18O and 16O isotopes as the energy of elastically scattered electrons depends on the mass of the scattering atom. Here we show that this approach is suitable for measuring oxygen self-diffusion in HfO2 using a Hf16O2 (20 nm)/Hf18O2 bilayers (60 nm). The mean depth probed is determined by the electron inelastic mean free path and is of the order of 15 nm in our experiment. Before annealing, the elastic peak from O is thus mainly due to electrons scattered from 16O in the outer layer, while after annealing the signal from 18O increases due to diffusion from the underlying Hf 18O2 layer. For high annealing temperatures the observed interdiffusion is consistent with an activation energy of 1 eV, but at lower temperatures interdiffusion decreases with increasing annealing time. We interpret this to be a consequence of defects, present in the layers early on and enhancing the oxygen diffusivity, disappearing during the annealing process.
    BibTeX:
    @article{Vos2014,
      author = {M. Vos and P.L. Grande and D.K. Venkatachalam and S.K. Nandi and R.G. Elliman},
      title = {Oxygen self-diffusion in HfO_2 studied by electron spectroscopy},
      journal = {Phys. Rev. Lett.},
      year = {2014},
      volume = {112},
      pages = {175901},
      url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.175901}
    }
    					
    Vos2014a Vos, M.; McEachran, R.P. & Zhu, L.F. A comparison of the theoretical and experimental results for keV electron scattering from argon 2014 Journal of Physics B: Atomic, Molecular and Optical Physics
    Vol. 47 , pp. 055201  
    article
    Abstract: Experiments studying the scattering of keV electrons from noble gas atoms have been done in the past, as the first Born approximation was thought to be valid under these conditions, and hence it was expected that these experiments could be modelled relatively straightforwardly by theory. Somewhat surprisingly these experiments have so far attracted only very limited theoretical interest and the ability of modern scattering theory to describe them has not been firmly established. In our earlier study of the cross section for the resonant transitions, we established that the first Born approximation was sufficient to describe the results for small scattering angles, but it did not account for the observed intensity at larger angles. Here we extend this comparison for the case of argon to monopole, quadrupole and octopole transitions below the continuum. The experimental results show differential cross sections spanning many orders of magnitude for these transitions. The relativistic distorted wave theory developed here describes these experiments for many transitions and a large range of scattering angles reasonably well.
    BibTeX:
    @article{Vos2014a,
      author = {M. Vos and R.P. McEachran and L.F. Zhu},
      title = {A comparison of the theoretical and experimental results for keV electron scattering from argon},
      journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      year = {2014},
      volume = {47},
      pages = {055201},
      url = {http://iopscience.iop.org/0953-4075/47/5/055201/}
    }
    					
    Vos2014b Vos, M.; Liu, X.; Grande, P.L.; Nandi, S.K.; Venkatachalam, D.K. & Elliman, R.G. The use of electron Rutherford backscattering to characterize novel electronic materials as illustrated by a case study of sputter-deposited NbO_x lms 2014 Nuclear Instruments & Methods B
    Vol. 340 , pp. 58 -62  
    article
    Abstract: Electrons scattered over large angles at relatively high energies (40 keV) are used to study NbOx lms. These lms were deposited by reactive sputter deposition on a Si substrate using a Nb target and an Ar/O2 gas mixture. Energy spectra of electrons scattered from such samples exhibit elastic scattering peaks for each components due to the energy di erence associated with scattering from di erent masses. This provides information about the lm thickness as well as its stoichiometry. The stoichiometry and the deposition rate depends on the concentration of O2 in the mixture. For Nb2O5-like lms the energy loss measurements also give an estimate of the band gap, but for Nb lms with lower O concentration the band gap is not resolved. This work illustrates the possibility to characterize modern transition metal oxide lms in a fairly simple electron scattering experiment.
    BibTeX:
    @article{Vos2014b,
      author = {M. Vos and X. Liu and P.L. Grande and S.K. Nandi and D.K. Venkatachalam and R.G. Elliman},
      title = {The use of electron Rutherford backscattering to characterize novel electronic materials as illustrated by a case study of sputter-deposited NbO_x lms},
      journal = {Nuclear Instruments & Methods B},
      year = {2014},
      volume = {340},
      pages = {58 -62},
      url = {http://dx.doi.org/10.1016/j.nimb.2014.06.024}
    }
    					
    Vos2014c Vos, M. & Grande, P.L. The relation between the electron energy loss spectra of hafnia and its dielectric function 2014 Surface Science
    Vol. 630 , pp. 1 -8  
    article
    Abstract: Recently two papers have been published deriving the dielectric function from hafnia from electron energy loss data. (Jin etal Applied Physics Letters 100 083713 (2006), Behar etal Phys. Rev A. 80 062901 (2009)). The obtained dielectric functions are compared in the optical limit and differ considerably. Here we try to clarify the situation by presenting new experimental data and review the analysis procedure used in the earlier work. We conclude that the discrepancy is most likely caused by a shortcoming in the way that the momentum-dependence of the dielectric function is modelled.
    BibTeX:
    @article{Vos2014c,
      author = {M. Vos and P.L. Grande},
      title = {The relation between the electron energy loss spectra of hafnia and its dielectric function},
      journal = {Surface Science},
      year = {2014},
      volume = {630},
      pages = {1 -8},
      url = {http://dx.doi.org/10.1016/j.susc.2014.06.008},
      doi = {https://doi.org/10.1016/j.susc.2014.06.008}
    }
    					
    Fadanelli2015 Fadanelli, R.C.; Behar, M.; Nagamine, L.C.C.M.; Vos, M.; Arista, N.R.; Garcia-Molina, R. & Abril, I. Energy loss function of condensed targets assessed by ion beam energy-loss measurements: Practical application to Ta2O5 films 2015 Journal of Physical Chemistry C
    Vol. 119 , pp. 20561  
    article
    Abstract: We present a study where the energy loss function (ELF) of Ta2O5, initially derived in the optical limit for only a limited region of excitation energies from Reflection Electron Energy Loss Spectroscopy (REELS) measurements, was improved and extended to the whole momentum and energy excitation region. This was done through a suitable theoretical analysis that includes the fulfillment of physically motivated restrictions, such as the f- and KK-sum rules. The target stopping cross section (SCS) and energy-loss straggling measured for 300-2000 keV proton and 200-6000 keV helium ion beams by means of Rutherford backscattering spectrometry (RBS) were compared to the same quantities calculated in the dielectric framework, showing an excellent agreement, which is used to judge the reliability of the Ta2O5 energy loss function. Based in this assessment we have also predicted the inelastic mean free path and the SCS of energetic electrons in Ta2O5.
    BibTeX:
    @article{Fadanelli2015,
      author = {R.C. Fadanelli and M Behar and L.C.C.M. Nagamine and M Vos and N.R. Arista and R. Garcia-Molina and I. Abril,},
      title = {Energy loss function of condensed targets assessed by ion beam energy-loss measurements: Practical application to Ta2O5 films},
      journal = {Journal of Physical Chemistry C},
      year = {2015},
      volume = {119},
      pages = {20561},
      url = {http://pubs.acs.org/doi/full/10.1021/acs.jpcc.5b04292},
      doi = {https://doi.org/10.1021/acs.jpcc.5b04292}
    }
    					
    Marmitt2015 Marmitt, G.; Rosa, L.F.S.; Nandi, S.K. & Vos, M. Analysis of mulit-layer ERBS spectra 2015 J. Electron Spectrosc. Relat. Phenom.
    Vol. 202 , pp. 26  
    article
    Abstract: A systematic way of analysis of multi-layer electron Rutherford Backscattering spectra is described. The approach uses fitting in terms of physical meaningful parameters. Simultaneous analysis then becomes possible for spectra taken at different incoming energies and measurement geometries.
    Examples are given to demonstrate the the level of detail that can be resolved by this technique.
    BibTeX:
    @article{Marmitt2015,
      author = {G. Marmitt and L.F.S. Rosa and S.K. Nandi and M. Vos},
      title = {Analysis of mulit-layer ERBS spectra},
      journal = {J. Electron Spectrosc. Relat. Phenom.},
      year = {2015},
      volume = {202},
      pages = {26},
      url = {http://dx.doi.org/10.1016/j.elspec.2015.02.009},
      doi = {https://doi.org/10.1016/j.elspec.2015.02.009}
    }
    					
    Moreh2015 Moreh, R.; Finkelstein, Y. & Vos, M. .. Comparison between electron and neutron Compton scattering studies 2015 proceedings 15th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics
    Vol. 93 , pp. 02011  
    article
    Abstract: We compare two techniques: Electron Compton Scattering (ECS) and neutron Compton scattering (NCS) and show that using certain incident energies, both can measure the atomic kinetic energy of atoms in molecules and solids. The information obtained is related to the Doppler broadening of nuclear levels and is very useful for deducing the widths of excited levels in many nuclei in self absorption measurements. A comparison between the atomic kinetic energies measured by the two methods on the same samples is made. Some results are also compared with calculated atomic kinetic energies obtained using the harmonic approximation where the vibrational frequencies were taken from IR/Raman optical measurements. The advantages of the ECS method are emphasized.
    BibTeX:
    @article{Moreh2015,
      author = {R. Moreh and Y. Finkelstein and M . Vos},
      title = {Comparison between electron and neutron Compton scattering studies},
      journal = {proceedings 15th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics},
      year = {2015},
      volume = {93},
      pages = {02011},
      url = {http://dx.doi.org/10.1051/epjconf/20159302011},
      doi = {https://doi.org/10.1051/epjconf/20159302011}
    }
    					
    Moreh2015a Moreh, R.; Finkelstein, Y. & Vos, M. Electron scattering as a tool to study zero-point kinetic energies of atoms in molecules 2015 Nuclear Instruments and Metods B
    Vol. 354 , pp. 37  
    article
    Abstract: High resolution electron Compton scattering (ECS) is being used to study the atomic momentum distributions and hence the zero-point kinetic energies (ZPKE) of the scattering atoms. Such studies have shown that the scattering is from a single atom of the scattering sample. For an electron beam with a well defined incident energy, the scattered electron energy at any angle from each atomic species is Doppler broadened. The broadening reflects the atomic momentum distribution contributed by both the internal and external motions of the molecular system. By measuring the energy broadening of the scattered electron lines it was possible to determine the kinetic energy of the scattering atom including that of its zero-point motion. Thus, the atomic kinetic energies in gases such as H2, D2, HD, CH4 and in H2O, D2O and NH3 were measured and compared with those calculated semi-empirically using the optical infra red (IR) and Raman frequencies of the internal vibrations of the molecules. In general, good agreement between the measured and calculated values was found. Electron scattering was also used to study the ratio of e-scattering intensities from the H- and O-atoms in water (H2O), where some anomalies were reported to exist.
    BibTeX:
    @article{Moreh2015a,
      author = {R. Moreh and Y. Finkelstein and M. Vos},
      title = {Electron scattering as a tool to study zero-point kinetic energies of atoms in molecules},
      journal = {Nuclear Instruments and Metods B},
      year = {2015},
      volume = {354},
      pages = {37},
      url = {http://dx.doi.org/10.1016/j.nimb.2014.11.078},
      doi = {https://doi.org/10.1016/j.nimb.2014.11.078}
    }
    					
    Rosa2015 Rosa, L.F.S.; Grande, P.L.; Dias, J.F.; Fadanelli, R.C. & Vos, M. Neutralization and wake effects on the Coulomb explosion of swift H_2^+ ions 2015 Phys. Rev. A
    Vol. 91 , pp. 042704  
    article
    Abstract: The Coulomb explosion of small cluster beams can be used to measure the dwell time of fragments traversing amorphous films. Therefore, the thickness of thin films can be obtained with the so-called Coulomb depth profiling technique using relatively high cluster energies where the fragments are fully ionized after breakup. Here we demonstrate the applicability of Coulomb depth profiling technique at lower cluster energies where neutralization and wake effects come into play. To that end, we used 50-150 keV/u H+ 2 molecular ions impinging on a 10nm TiO2 film and measured the energy of the backscattered H+ fragments with a high energy resolution. The effect of the neutralization of the H+ fragments along the incoming trajectory before the backscattering collision is clearly observed at lower energies through the decrease of the energy broadening due to the Coulomb explosion. The reduced values of the Coulomb explosion combined with full Monte-Carlo simulations provide compatible results with those obtained at higher cluster energies where neutralization is less important. The results are corroborated by electron microscopy measurements.
    BibTeX:
    @article{Rosa2015,
      author = {L.F.S. Rosa and P.L. Grande and J.F. Dias and R.C. Fadanelli and M. Vos},
      title = {Neutralization and wake effects on the Coulomb explosion of swift H_2^+ ions},
      journal = {Phys. Rev. A},
      year = {2015},
      volume = {91},
      pages = {042704},
      url = {http://dx.doi.org/10.1103/PhysRevA.91.042704},
      doi = {https://doi.org/10.1103/PhysRevA.91.042704}
    }
    					
    Vos2015 Vos, M.; Winkelmann, A. & Nolze, G. Element-specific Kikuchi patterns of Rutile 2015 Ultramicroscopy
    Vol. 156 , pp. 50  
    article
    Abstract: The kinetic energy of keV electrons backscattered from a rutile (TiO_2) surface depends measurably on the mass of the scattering atom. This makes it possible to determine separately the angular distribution of electrons backscattered elastically from either Ti or O. Diffraction effects of these backscattered electrons inside the rutile crystal lead to the formation of Kikuchi patterns. The element-resolved Kikuchi patterns of Ti and O differ characteristically, but each can be described fairly well in terms of the dynamical theory of diffraction.
    Qualitatively, much of the differences can be understood by considering the physical arrangement of the Ti and O atoms in the relevant lattice planes.
    BibTeX:
    @article{Vos2015,
      author = {M. Vos and A. Winkelmann and G. Nolze},
      title = {Element-specific Kikuchi patterns of Rutile},
      journal = {Ultramicroscopy},
      year = {2015},
      volume = {156},
      pages = {50},
      url = {http://dx.doi.org/10.1016/j.ultramic.2015.04.018},
      doi = {https://doi.org/10.1016/j.ultramic.2015.04.018}
    }
    					
    Vos2015a Vos, M. & Grande, P.L. High-energy electron scattering from TiO_2 surfaces 2015 Nuclear Instruments & Methods B
    Vol. 354 , pp. 332  
    article
    Abstract: Electron scattering experiments at keV energies from a TiO_2 surface are presented. The paper aims to give an overview of the wide variety of information that can be extracted from such experiments. If the elastic scattering cross sections are known these experiments give the sample composition, if the composition is known one can extract the ratio of the elastic cross sections. In the experiments described here the ratio of the Ti and O cross sections deviates noticeably from the one calculated from the Rutherford formula. The peak widths give access to the mean kinetic energies of the atoms present. We show that the mean kinetic energy of Ti atoms is less than that of O atoms, but both kinetic energies are still affected by quantum effects, i.e. are larger than 3/2 kT. We extract an estimate of the dielectric function of TiO_2 by extending the measurement up to 100 eV energy loss. At these high energies the determination of the dielectric function from the measured energy loss spectrum is relatively simple, as the contribution of surface excitations is small and the obtained spectrum deviates only little from the dielectric function in the optical limit. Finally, we use the technique to monitor the surface after sputtering with Ar^+ ions, and observe both differences in composition and electronic structure induced by sputtering that disappear again after annealing.
    BibTeX:
    @article{Vos2015a,
      author = {M. Vos and P.L. Grande},
      title = {High-energy electron scattering from TiO_2 surfaces},
      journal = {Nuclear Instruments & Methods B},
      year = {2015},
      volume = {354},
      pages = {332},
      url = {http://dx.doi.org/10.1016/j.nimb.2014.11.083},
      doi = {https://doi.org/10.1016/j.nimb.2014.11.083}
    }
    					
    Vos2015b Vos, M.; Marmitt, G.G.; Finkelstein, Y. & Moreh, R. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra 2015 Journal of Chemical Physics
    Vol. 143 , pp. 104203  
    article
    Abstract: Reflection electron energy loss spectra from some insulating materials (CaCO_3, Li_2CO_3 and SiO_2) taken at relatively high incoming electron energies (5 to 40 keV) are analyzed. Here one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected tothe mean kinetic energy of the atom in the material (Doppler broadening). The experimentally-obtained mean kinetic energies of the O, C, Li, Ca and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO_2 a good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E-E_rm gap)^3/2 . For CaCO_3 the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li_2CO_3 (7.5 eV) is the first experimental estimate.
    BibTeX:
    @article{Vos2015b,
      author = {M. Vos and G.G. Marmitt and Y. Finkelstein and R. Moreh},
      title = {Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra},
      journal = {Journal of Chemical Physics},
      year = {2015},
      volume = {143},
      pages = {104203},
      url = {http://dx.doi.org/10.1063/1.4929911},
      doi = {https://doi.org/10.1063/1.4929911}
    }
    					
    Vos2015c Vos, M. A model dielectric function for low and very high momentum transfer 2015 Nuclear Instruments & MethodsB
    Vol. 366 , pp. 6  
    article
    Abstract: A model dielectric function is derived for TiO_2 based on reflection electron energy loss spectroscopy data and photoabsorption cross sections. The model is based on a set of Mermin oscillators. The input data is dominated by excitations at low momentum transfer, i.e. near the optical limit. Surprisingly the dielectric function derived at low momentum transfer describes the Compton profile quite well, while approaches based on Drude oscillatorsfail dramatically. The link between the dielectric function in the high-momentum transfer limit and a Compton profile is discussed. The underlying reason why the Mermin approach, which is based on a free electron model, is successful in describing the Compton profile is tentatively discussed.
    BibTeX:
    @article{Vos2015c,
      author = {M. Vos},
      title = {A model dielectric function for low and very high momentum transfer},
      journal = {Nuclear Instruments & MethodsB},
      year = {2015},
      volume = {366},
      pages = {6},
      url = {http://doi.org/10.1016/j.nimb.2015.09.091},
      doi = {https://doi.org/10.1016/j.nimb.2015.09.091}
    }
    					
    Vos2016 Vos, M.; Marmit, G.G. & Grande, P.L. A comparison of measured ERBS spectra of oxide containing samples with results of Monte Carlo simulations 2016 Surface and Interface Analysis
    Vol. 48 , pp. 415  
    article
    Abstract: Electron Rutherford backscattering is a technique that can be used to measure the composition of the near-surface area of samples quantitatively. For interpretation one usually relies on the single-scattering approximation. Here we present results of 4 samples, containing oxygen and other species, varying from very light to very heavy. A Monte Carlo code is described that models these measurements. From these simulations it is clear that for all samples multiple scattering occurs frequently, but also that the single scattering interpretation deduces the right composition, except for O atoms in a very heavy matrix, where interpretation is less straight-forward. The width of the peaks, related to Doppler broadening of the signal of electrons scattering from vibrating atoms, is somewhat more sensitive to multiple scattering effects.
    BibTeX:
    @article{Vos2016,
      author = {M. Vos and G.G. Marmit and P.L. Grande},
      title = {A comparison of measured ERBS spectra of oxide containing samples with results of Monte Carlo simulations},
      journal = {Surface and Interface Analysis},
      year = {2016},
      volume = {48},
      pages = {415},
      url = {http://doi.org/10.1002/sia.5948},
      doi = {https://doi.org/10.1002/sia.5948}
    }
    					
    Vos2016a Vos, M. Lineshape analysis of keV electrons scattered from hydrogen molecules 2016 Journal of Physics B: Atomic, Molecular and Optical Physics
    Vol. 49 , pp. 145202  
    article
    Abstract: Accurate measurements of keV electrons scattered elastically from H2 molecules reveal a line shape that is an intrinsic property of the target. The intrinsic width of the elastic peak is due to the non-zero momentum of a proton bound to a molecule. A more precise analysis of the line shape shows that it deviates from Gaussian. This deviation is shown to be a consequence of the dominance of the momentum component of the protons along the molecular axis. The mean-kinetic energy of the protons in H_2 obtained based on the new peak shape agrees better with theory than the one obtained based on a Gaussian peak shape. These measurements demonstrate thus the possibility of a new way to study the dynamics of nuclei by electron scattering.
    BibTeX:
    @article{Vos2016a,
      author = {M. Vos},
      title = {Lineshape analysis of keV electrons scattered from hydrogen molecules},
      journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      year = {2016},
      volume = {49},
      pages = {145202},
      url = {http://doi.org/10.1088/0953-4075/49/14/145202}
    }
    					
    Vos2016b Vos, M.; King, S.W. & French, B.L. Measurement of the band gap by reflection energy loss spectroscopy 2016 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 212 , pp. 74  
    article
    Abstract: We investigate the possibilities of measuring the band gap of avariety of semiconductors and insulators by reflection electron energy loss spectroscopy without additional surface preparation. The band gap is a bulk property, whereas reflection energy loss spectroscopy is generally considered a surface sensitive technique. By changing the energy of the incoming electrons, the degree of surface sensitivity can be changed. Here, we present a number of case studies to determine the optimum condition for the determination of the band gap. At very large incoming electron energies recoil effects interfere with the band gap determination, whereas at very low energies surface effects are obscuring the band gap without surface preparation. Using an incoming energy of 5 keV a reasonable estimate of the band gap is obtained in most cases.
    BibTeX:
    @article{Vos2016b,
      author = {M. Vos and S. W. King and B.L. French},
      title = {Measurement of the band gap by reflection energy loss spectroscopy},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2016},
      volume = {212},
      pages = {74},
      url = {http://doi.org/10.1016/j.elspec.2016.08.001}
    }
    					
    Vos2016c Vos, M. & Winkelmann, A. Two-dimensional Kikuchi patterns of Si as measured using an electrostatic analyser 2016 Ultramicroscopy
    Vol. 171 , pp. 19  
    article
    Abstract: We present Kikuchi patterns of Si single crystals measured with an electrostatic analyser, where the kinetic energy of the diffracted electron is known with sub-eV precision. Two-dimensional patterns are acquired by rotating the crystal under computer control. This makes detailed comparison of calculated and measured distributions possible with precise knowledge of the energy of the electron. The case of Si is used to validate the method, and these experiments provide a detailed comparison of measured and calculated Kikuchi patterns. In this way, we can gain more insight on Kikuchi pattern formation in non-energy resolved measurements of conventional electron backscatter diffraction (EBSD) and electron channeling patterns (ECP). It was possible to identify the influence of channeling of the incoming beam on the measured Kikuchi pattern. The effect of energy loss on the Kikuchi pattern was established, and it is demonstrated that, under certain conditions, the channeling features have a different dependence on the energy loss compared to the Kikuchi lines.
    BibTeX:
    @article{Vos2016c,
      author = {M. Vos and A. Winkelmann},
      title = {Two-dimensional Kikuchi patterns of Si as measured using an electrostatic analyser},
      journal = {Ultramicroscopy},
      year = {2016},
      volume = {171},
      pages = {19},
      url = {http://doi.org/10.1016/j.ultramic.2016.08.015}
    }
    					
    Winkelmann2016 Winkelmann, A.; Nolze, G.; Vos, M.; Salvat-Pujol, F. & Werner, W. Physics-based Simulation Models for EBSD: Advances and Challenges 2016 IOP Conference Series.
    Vol. 109 , pp. 012018  
    article
    Abstract: EBSD has evolved into an effective tool for microstructure investigations in the scanning electron microscope. The purpose of this contribution is to give an overview of various simulation approaches for EBSD Kikuchi patterns and to discuss some of the underlying physical mechanisms.
    BibTeX:
    @article{Winkelmann2016,
      author = {A. Winkelmann and G. Nolze and M. Vos and F. Salvat-Pujol and W. Werner},
      title = {Physics-based Simulation Models for EBSD: Advances and Challenges},
      journal = {IOP Conference Series.},
      year = {2016},
      volume = {109},
      pages = {012018},
      url = {http://iopscience.iop.org/article/10.1088/1757-899X/109/1/012018},
      doi = {https://doi.org/10.1088/1757-899X/109/1/012018}
    }
    					
    Marmitt2017 Marmitt, G.G.; Nandi, S.K.; Venkatachalam, D.K.; Elliman, R.G.; Vos, M. & Grande, P.L. Diffusion in TiO_2 films studied by electron- and ion-RBS 2017 Thin Solid Films
    Vol. 629 , pp. 97  
    article
    Abstract: The diffusivity of oxygen in thin, sputter-deposited TiO_2 films, as can be used in RRAMs, is measured using electron and ion backscattering techniques. The as-grown sample consisted of two layers (Ti^16O_2 and Ti^18O_2) and was annealed between 500degree and 900degree. Excellent consistency was found for the diffusion as measured by the electron and ion-based techniques. The extent of diffusion was much larger than expected from the literature data for O diffusion in single-crystal rutile, suggesting that defects in the sputter-deposited film play an essential role in the diffusion process.
    BibTeX:
    @article{Marmitt2017,
      author = {G.G. Marmitt and S.K. Nandi and D.K. Venkatachalam and R.G. Elliman and M. Vos and P.L. Grande},
      title = {Diffusion in TiO_2 films studied by electron- and ion-RBS},
      journal = {Thin Solid Films},
      year = {2017},
      volume = {629},
      pages = {97},
      url = {http://dx.doi.org/10.1016/j.tsf.2017.03.024}
    }
    					
    Vos2017 Vos, M. & Grande, P.L. Simple model dielectric functions for insulators 2017 Journal of Physical and Chemistry of Solids
    Vol. 104 , pp. 192  
    article
    Abstract: The Drude dielectric function is a simple way of describing the dielectric function of free electron materials, which have an uniform electron density in a classical way. The Mermin dielectric function describes a free electron gas, but is based on quantum physics. More complex metals have varying electron densities and are often described by a sum of Drude dielectric functions, the weight of each function being taken proportional to the volume with the corresponding density. Here we describe a slight variation on the Drude dielectric functions that describes insulators in a semi-classical way and a form of the Levine-Louie dielectric function including a relaxation time that does the same within the framework of quantum physics. In the optical limit the semi-classical description of an insulator and the quantum physics description coincide, in the same way as the Drude and Mermin dielectric function coincide in the optical limit for metals. There is a simple relation between the coeffcients used in the classical and quantum approaches, a relation that ensures that the obtained dielectric function corresponds to the right static refractive index. For water we give a comparison of the model dielectric function at non-zero momentum with inelastic X-ray measurements, both at relative small momenta and in the Compton limit. The Levine-Louie dielectric function including a relaxation time describes the spectra at small momentum quite well, but in the Compton limit there are significant deviations.
    BibTeX:
    @article{Vos2017,
      author = {M. Vos and P.L. Grande},
      title = {Simple model dielectric functions for insulators},
      journal = {Journal of Physical and Chemistry of Solids},
      year = {2017},
      volume = {104},
      pages = {192},
      url = {http://doi.org/10.1016/j.jpcs.2016.12.015},
      doi = {https://doi.org/10.1016/j.jpcs.2016.12.015}
    }
    					
    Vos2017a Vos, M. & Grande, P.L. Extracting dielectric function from high-energy REELS measurements 2017 Surface and Interface Analysis
    Vol. 49 , pp. 808-821  
    article
    Abstract: A method is described for extracting the dielectric function directly from a reflection electron energy loss spectrum taken at relatively high energies (2.5 to 40 keV). It makes simplifying assumptions on separation of surface and bulk losses. The approach uses a description based on partial intensities and surface excitation parameters and fits directly the reflection electron energy loss data. Several different model dielectric functions are implemented (extended Drude, Drude Lindhard, Mermin, and the Levine–Louie dielectric functions with relaxation time), and their advantages and disadvantages are discussed. Justification of this approach is in the end based on a comparison with the dielectric function as obtained by other means, which is generally quite good, provided that the solution obtained is restrained by sum rules to the right refractive index and electron density. The fitting program, to be used in conjunction with commercial plotting software, is provided.
    BibTeX:
    @article{Vos2017a,
      author = {M. Vos and P.L. Grande},
      title = {Extracting dielectric function from high-energy REELS measurements},
      journal = {Surface and Interface Analysis},
      year = {2017},
      volume = {49},
      pages = {808--821},
      url = {http://doi.org/10.1002/sia.6227},
      doi = {https://doi.org/10.1002/sia.6227}
    }
    					
    Vos2017b Vos, M. & Winkelmann, A. Element-resolved Kikuchi pattern measurements of non-centrosymmetric materials, 2017 Materials Characterization
    Vol. 123 , pp. 328-338  
    article
    Abstract: Angle-resolved electron Rutherford backscattering (ERBS) measurements using an electrostatic electron energy analyser can provide unique access to element-resolved crystallographic information. We present Kikuchi patterns measurements of the non-centrosymmetric crystal GaP, separately resolving the contributions of electrons backscattered from Ga and P. In comparison to element-integrated measurements like in the method of electron backscatter diffraction (EBSD), the effect of the absence of a proper 4-fold rotation axis in the point group of GaP can be sensed with a much higher visibility via the element-resolved Ga to P intensity ratio. These element-resolved measurements make it possible to experimentally attribute the previously observed point-group dependent effect in element-integrated EBSD measurements to the larger contribution of electrons scattered from Ga compared to P. The absence of a clear peak for electrons scattered from Ga for the 110] zone axis, as experimentally observed here, is confirmed by theoretical simulations.
    BibTeX:
    @article{Vos2017b,
      author = {M. Vos and A. Winkelmann},
      title = {Element-resolved Kikuchi pattern measurements of non-centrosymmetric materials,},
      journal = {Materials Characterization},
      year = {2017},
      volume = {123},
      pages = {328--338},
      url = {http://doi.org/10.1016/j.matchar.2016.11.043},
      doi = {https://doi.org/10.1016/j.matchar.2016.11.043}
    }
    					
    Vos2017c Vos, M. & Grande, P.L. How the choice of model dielectric function affects the calculated observables 2017 Nucleal Instruments and Methods B
    Vol. 407 , pp. 97  
    article
    Abstract: It is investigated how the model used to describe a dielectric function (i.e. a Mermin, Drude, Drude-Lindhard, Levine-Louie with relaxation time dielectric function) affects the interpretation of a REELS experiment, the calculation of the electron inelastic mean free path as well proton stopping and straggling. Three dielectric functions are constructed that are based on different models describing a metal, but have identical loss functions in the optical limit. A loss function with the same shape, but half the amplitude, is used to derive four different model dielectric functions for an insulator. From these dielectric functions we calculate the differential inverse mean free path, the mean free path itself, as well as the stopping force and straggling for protons. The similarity of the underlying physics between proton stopping, straggling and the electron inelastic mean free path is stressed by describing all three in terms of the differential inverse inelastic mean free path. To further highlight the reason why observed quantities depend on the model dielectric function used we study partial differential inverse inelastic mean free paths, i.e. those obtained by integrating over only a limited range of momentum transfers. In this way it becomes quite transparent why the observable quantities depend on the choice of model dielectric function.
    BibTeX:
    @article{Vos2017c,
      author = {M. Vos and P.L. Grande},
      title = {How the choice of model dielectric function affects the calculated observables},
      journal = {Nucleal Instruments and Methods B},
      year = {2017},
      volume = {407},
      pages = {97},
      url = {doi.org/10.1016/j.nimb.2017.05.064}
    }
    					
    Winkelmann2017 Winkelmann, A.; Nolze, G.; Vespucci, S.; Gunasekar, N.K.; Trager-Cowan, C.; Vilalta-Clemente, A.; Wilkinson, A.J. & Vos, M. Diffraction-modulated electron transport in microscopic imaging applications 2017 Journal of Microscopy
    Vol. 267 , pp. 330-346  
    article
    Abstract: We analyze the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Speciffcally, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolor orientation imaging using multiple, angle-resolving detectors. Consequently, diffraction effects of the incident beam and their impact on the subsequent coherent and incoherent electron transport need to be taken into account for an in-depth theoretical modeling of the energy- and momentum distribution of electrons backscattered from crystalline sample regions. Our findings have implications for the level of theoretical detail that can be necessary for the interpretation of complex imaging modalities such as electron channeling contrast imaging (ECCI) of defects in crystals. If the solid angle of detection is limited to specific regions of the backscattered electron momentum distribution, the image contrast that is observed in ECCI and similar applications can be strongly affected by incident beam dffraction and topographic effects from the sample surface. As an application, we demonstrate characteristic changes in the resulting images if different properties of the backscattered electron distribution are used for the analysis of a GaN thin film sample containing dislocations.
    BibTeX:
    @article{Winkelmann2017,
      author = {A. Winkelmann and G. Nolze and S. Vespucci and N.K. Gunasekar and C. Trager-Cowan and A.  Vilalta-Clemente and A.J. Wilkinson and M. Vos},
      title = {Diffraction-modulated electron transport in microscopic imaging applications},
      journal = {Journal of Microscopy},
      year = {2017},
      volume = {267},
      pages = {330--346},
      url = {http://doi.org/10.1111/jmi.12571},
      doi = {https://doi.org/10.1111/jmi.12571}
    }
    					
    Alotiby2018 Alotiby, M.; Greguric, I.; Kibédi, T.; Lee, B.Q.; Roberts, M.; Stuchbery, A.E.; andT. Tornyi, P.T. & Vos, M. Measurement of the intensity ratio of Auger and conversion electrons for the case of ^125I 2018 Physics in Medicine & Biology
    Vol. 63 , pp. 06NT04  
    article
    Abstract: Auger electrons emitted after nuclear decay have potential application in targeted cancer therapy. For this purpose it is important to know the Auger electron yield per nuclear decay. In this work we describe a measurement of the ratio of the number of conversion electrons (emitted as part of the nuclear decay process) to the number of Auger electrons (emitted as part of the atomic relaxation process after the nuclear decay) for the case of 125I. Results are compared with Monte-Carlo type simulations of the relaxation cascade using the BrIccEmis code. Our results indicate that for 125I the calculations based on rates from the Evaluated Atomic Data Library underestimate the K Auger yields by 20%.
    BibTeX:
    @article{Alotiby2018,
      author = {M. Alotiby and I. Greguric and T. Kibédi and B.Q. Lee and M. Roberts and A.E. Stuchbery and Pi Tee andT. Tornyi and M. Vos},
      title = {Measurement of the intensity ratio of Auger and conversion electrons for the case of ^125I},
      journal = {Physics in Medicine & Biology},
      year = {2018},
      volume = {63},
      pages = {06NT04},
      url = {https://doi.org/10.1088/1361-6560/aab24b},
      doi = {https://doi.org/10.1088/1361-6560/aab24b}
    }
    					
    Nandi2018 Nandi, S.K.; Venkatachalam, D.K.; Ruffell, S.; England, J.; Grande, P.; Vos, M. & Elliman, R.G. Room Temperature Synthesis of HfO_2/HfO_x Heterostructures by Ion-implantation 2018 Nanotechnology
    Vol. 29 , pp. 425601  
    article
    Abstract: Implantation of Hf films with oxygen ions is shown to be an effective means of fabricating high-quality HfO2/HfO x heterostructures at room temperature, with the layer composition and thicknesses determined by the ion energy and fluence. Implantation with 3 keV O+ ions to a fluence of 1 × 10^17 ions cm^−2 produces a polycrystalline (monoclinic-) HfO2 layer extending from the surface to a depth of  12 nm, and an underlying graded HfO x layer extending an additional  7 nm, while implantation with 6 keV O to a similar fluence produces a near-stoichiometric surface layer of 7 nm thickness and a graded substoichiometric layer extending to depth of  30 nm. These structures are shown to be broadly consistent with oxygen range data but more detailed comparison with dynamic Monte Carlo simulations suggests that the near-surface region contains more oxygen than expected from collisional processes alone. The bandgap and dielectric strength of the HfO2 layer produced by 3 keV; 1 × 10 ^17 ions cm^−2 implant is shown to be indistinguishable from those of an amorphous film deposited by atomic layer deposition at 200 °C. The utility of these layers is demonstrated by studying the resistive switching properties of metal-oxide-metal test structures fabricated by depositing a top metal contact on the implanted film. These results demonstrate the suitability of ion-implantation for the synthesis of functional oxide layers at room temperature.
    BibTeX:
    @article{Nandi2018,
      author = {S. K. Nandi and D. K. Venkatachalam and S. Ruffell and J. England and P. Grande and M. Vos and R. G. Elliman},
      title = {Room Temperature Synthesis of HfO_2/HfO_x Heterostructures by Ion-implantation},
      journal = {Nanotechnology},
      year = {2018},
      volume = {29},
      pages = {425601},
      url = {http://iopscience.iop.org/article/10.1088/1361-6528/aad756/meta}
    }
    					
    Trombini2018 Trombini, H.; Grande, P.L.; Hentz, A.; Vos, M. & Winkelmann, A. A comparison of the analysis of non-centrosymmetric materials based on ion and electron beams 2018 Nuclear Instruments and Methods B,
    Vol. 431 , pp. 31  
    article
    Abstract: Techniques like electron backscattered diraction (EBSD) and angle-resolved electron Rutherford backscattering (ERBS) are sensitive to the lack of in-version symmetry in crystals and hence can determine the absolute crystal orientation. In this paper we demonstrate for the case of GaP that medium energy ion scattering (MEIS) can also be used to obtain the absolute crystal orientation. A comparison between the 2D-backscattering intensities as a function of the detection directions for electrons (as is measured in EBSD or ERBS) and protons (as is measured in MEIS) is made and discussed in terms of diraction and classical subchanneling respectively.
    BibTeX:
    @article{Trombini2018,
      author = {Trombini, H. and Grande, P. L. and Hentz, A. and Vos, M. and Winkelmann, A.},
      title = {A comparison of the analysis of non-centrosymmetric materials based on ion and electron beams},
      journal = {Nuclear Instruments and Methods B,},
      year = {2018},
      volume = {431},
      pages = {31},
      url = {https://doi.org/10.1016/j.nimb.2018.06.026},
      doi = {https://doi.org/10.1016/j.nimb.2018.06.026}
    }
    					
    Vos2018a Vos, M.; Grande, P.L. & Marmitt, G.G. The influence of shallow core levels on the shape of REELS spectra 2018 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 229 , pp. 42 - 46  
    article
    Abstract: It is well established that the shape of spectra acquired using reflection electron energy loss spectroscopy (REELS) is determined by the dielectric function. Extracting the dielectric function from REELS spectra is a real challenge as it is governed by strong multiple scattering. It is generally assumed that the contribution of shallow core levels (with binding energies over 100 eV) to the REELS data can be neglected when one interprets valence band REELS data that usually extends to, at most, 100 eV energy loss. Here we show that, especially when incoming energies over 1 keV are used, this is not the case and that the intensity of the REELS spectrum can only be calculated correctly if the shallow core levels are taken into account. The implications for this for the extraction of the dielectric function from REELS data is discussed.
    BibTeX:
    @article{Vos2018a,
      author = {M. Vos and P.L. Grande and G.G. Marmitt},
      title = {The influence of shallow core levels on the shape of REELS spectra},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2018},
      volume = {229},
      pages = {42 -- 46},
      url = {https://doi.org/10.1016/j.elspec.2018.09.006},
      doi = {https://doi.org/10.1016/j.elspec.2018.09.006}
    }
    					
    Alotiby2019 Alotiby, M.; Greguric, I.; Kibédid, T.; Tee, B. & Vos, M. Quantitative electron spectroscopy of ^125I over an extended energy range 2019 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 232 , pp. 73 - 82  
    article
    Abstract: Auger electrons emitted after nuclear decay have potential application in targeted cancer therapy. For this purpose it is important to know the Auger electron yield per nuclear decay. In this work we measure the ratio of the number of conversion electrons (emitted as part of the nuclear decay process) and the number of Auger electrons (emitted as part of the atomic relaxation process after the nuclear decay) for the case of ^125I. Results are compared with Monte-Carlo type simulations of the relaxation cascade using the BrIccEmis code. With the appropriate choice of parameters this program describes the observed spectra quite well over the whole energy range.
    BibTeX:
    @article{Alotiby2019,
      author = {M. Alotiby and I. Greguric and T. Kibédid and B. Tee and M. Vos},
      title = {Quantitative electron spectroscopy of ^125I over an extended energy range},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2019},
      volume = {232},
      pages = {73 - 82},
      url = {https://doi.org/10.1016/j.elspec.2019.02.009},
      doi = {https://doi.org/10.1016/j.elspec.2019.02.009}
    }
    					
    Matias2019 Matias, F.; Grande, P.L.; Vos, M.; Koval, P.; Koval, N.E. & Arista, N.R. Non-linear stopping effects of slow ions in a non-free electron system: titanium nitride, 2019 Phys. Rev. A
    Vol. 100 , pp. 030701  
    article
    Abstract: A recent experimental study of the energy losses of various ions in titanium nitride, in the low-energy range [M. A. Sortica et al., Sci. Rep. 9, 176 (2019)], showed a striking departure of the measured values from those predicted by density functional theory. They suggested electron promotion in atomic collisions between dressed atoms as an explanation. In this Rapid Communication, we investigate the process of energy loss of slow ions in TiN using theoretical formulations that are based, on one side, on self-consistent models of nonlinear screening and quantum scattering theory, and on the other, on ab initio computations of the electron-density profile of titanium nitride. Two theoretical approaches are considered to determine the average energy transfer: One is based on the local-density approximation for the inhomogeneous electron gas corresponding to the calculated
    density of TiN, and the other is based on the Penn model for the convolution of the inhomogeneous electron-gas response based on a measured electron-loss function. Both approaches produce very similar results and are in remarkable agreement with the experimental data, indicating that the observed enhancement in the energy-loss values is due to the contribution of a range of electron densities in the TiN compound.
    BibTeX:
    @article{Matias2019,
      author = {F. Matias and P.L. Grande and M. Vos and P. Koval and N.E. Koval and N.R. Arista},
      title = {Non-linear stopping effects of slow ions in a non-free electron system: titanium nitride,},
      journal = {Phys. Rev. A},
      year = {2019},
      volume = {100},
      pages = {030701},
      url = {https://doi.org/10.1103/PhysRevA.100.030701},
      doi = {https://doi.org/10.1103/PhysRevA.100.030701}
    }
    					
    Sulzbach2019 Sulzbach, M.C.; Selau, F.F.; Trombini, H.; Grande, P.L.; Marmitt, G.G.; Pereira, L.G.; Vos, M. & Elliman, R.G. Characterization of oxygen self-diffusion in TiO2 resistive-switching layers by nuclear reaction profiling 2019 Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
    Vol. 441 , pp. 8-11  
    article
    Abstract: Oxygen self-diffusion was investigated in TiO_2 layers employed for resistive-switching memories using resonant nuclear reaction profiling (NRP) and ^18O labeling. The layers were grown using physical vapor deposition technique (sputtering) and were polycrystalline. The diffusivity was measured over the temperature range 600–800 °C and the activation energy for oxygen self-diffusion in sputter-deposited TiO_2 films determined to be 1.09 ± 0.16 eV, a value consistent with results obtained by previous studies (Marmitt et al., 2017).
    BibTeX:
    @article{Sulzbach2019,
      author = {M.C. Sulzbach and F.F. Selau and H. Trombini and P.L. Grande and G.G. Marmitt and L.G. Pereira and M. Vos and R.G. Elliman},
      title = {Characterization of oxygen self-diffusion in TiO2 resistive-switching layers by nuclear reaction profiling},
      journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
      year = {2019},
      volume = {441},
      pages = {8--11},
      url = {https://doi.org/10.1016/j.nimb.2018.11.026},
      doi = {https://doi.org/10.1016/j.nimb.2018.11.026}
    }
    					
    Tee2019 Tee, B.P.E.; Vos, M.; Stuchbery, A.E.; Dowie, J.T.H.; Alotiby, M.; Lee, B.Q.; Greguric, I. & Kibédi, T. High resolution conversion electron spectroscopy of the ^125I EC-decay, 2019 Physical Review C
    Vol. 100 , pp. 034313  
    article
    Abstract: The conversion electrons from the decay of the 35.5-keV excited state of 125Te following the electron capture decay of 125I have been investigated at high resolution using an electrostatic spectrometer. The penetration parameter lambda = -1:2(6) and mixing ratio delta(E2/M1)j = 0:015(2) were deduced by fitting to literature values and present data. The shake probability of the conversion electrons is estimated to be 0.5, more than two times larger than the predicted value of 0.2.
    BibTeX:
    @article{Tee2019,
      author = {B.P.E. Tee and M. Vos and A.E. Stuchbery and J.T.H. Dowie and M. Alotiby and B.Q. Lee and I. Greguric and T. Kibédi},
      title = {High resolution conversion electron spectroscopy of the ^125I EC-decay,},
      journal = {Physical Review C},
      year = {2019},
      volume = {100},
      pages = {034313},
      url = {https://doi.org/10.1103/PhysRevC.100.03431},
      doi = {https://doi.org/10.1103/PhysRevC.100.03431}
    }
    					
    Trombini2019 Trombini, H.; , I.A.; Marmitt, G.G.; Fadanelli, R.; Grande, P.L.; Vos, M. & England, J.G. Profiling As plasma doped Si/SiO_2 with molecular ions 2019 Thin Solid Films
    Vol. 692 , pp. 137536  
    article
    Abstract: Arsenic profiles in plasma doped silicon wafers were traced by scattering of H^+ and H_2 ions at medium energies. Two wafers were doped with the same bias, gas pressure, total implanted dose and AsH_3 concentration. After implantation, the wafers were submitted to industrial cleaning processes and one wafer was subjected to an additional thermal treatment. Scattering spectra of single and molecular ion beams with the same energy per nucleon and charge state differed only by the energy broadening due to the break-up of the molecule, allowing depth profiling by calculation of the dwell time before the backscattering collision. On average, we observed a density reduction of 13% in the SiO_2 overlayer grown after the implantation pro-cess. In addition, the arsenic depth-profile determined were in close agreement with independent findings obtained by electron techniques.
    BibTeX:
    @article{Trombini2019,
      author = {H. Trombini and, I. Alencar and G. G. Marmitt and R. Fadanelli and P. L. Grande and M. Vos and J. G. England},
      title = {Profiling As plasma doped Si/SiO_2 with molecular ions},
      journal = {Thin Solid Films},
      year = {2019},
      volume = {692},
      pages = {137536},
      doi = {https://10.1016/j.tsf.2019.137536}
    }
    					
    Vos2019 Vos, M. & Grande, P.L. Modeling the contribution of semi-core electrons to the dielectric function 2019 Journal of Physics and Chemistry of Solids
    Vol. 124 , pp. 242 - 249  
    article
    Abstract: Many aspects of the interaction of charged particles with matter can be expressed in terms of the dielectric function ε ( q). The dielectric function is relatively well known in the optical limit (q=0) but, for example, stopping power calculations require the knowledge of the dielectric function for qne 0. Several approaches have been used to extend the dielectric function to qne 0 for both the valence electrons, using variations of the Lindhard dielectric function and the core levels where an atomic description can be used. The intermediate case of shallow core levels is somewhat problematic. Here collective effects modify the atomic picture, and the hydrogenic approximation of the wave function is less accurate. In this paper we describe a new extension scheme of the contribution to the energy loss function of shallow core levels to qne 0 and show that tor Al and Si it describes the experimental stopping data somewhat better than previous approaches. It also describes reasonably well the proton and electron induced ionisation cross section of these shallow core levels. Lastly we investigate the dielectric function in the limit of high-q, where it can be interpreted as a Compton profile. An approximation scheme in terms of Mermin dielectric function with an amplitude that depends on q works in all cases quite well.
    BibTeX:
    @article{Vos2019,
      author = {Vos, M. and Grande, P. L.},
      title = {Modeling the contribution of semi-core electrons to the dielectric function},
      journal = {Journal of Physics and Chemistry of Solids},
      year = {2019},
      volume = {124},
      pages = {242 - 249},
      url = {https://doi.org/10.1016/j.jpcs.2018.09.020},
      doi = {https://doi.org/10.1016/j.jpcs.2018.09.020}
    }
    					
    Vos2019a Vos, M. & Grande, P.L. Extension schemes of the dielectric function, and their implications for ion stopping calculations 2019 Journal of Physics and Chemistry of Solids
    Vol. 133 , pp. 187 -196  
    article
    Abstract: The dielectric function is often known in the optical limit (zero momentum) but knowledge away from zero momentum is required for the calculation of many physical properties, such as ion stopping and inelastic mean free path. We review the several extension schemes and compare the results with the available literature and investigate in particular the eect of the extension scheme on the calculated proton stopping.
    BibTeX:
    @article{Vos2019a,
      author = {M. Vos and P.L. Grande},
      title = {Extension schemes of the dielectric function, and their implications for ion stopping calculations},
      journal = {Journal of Physics and Chemistry of Solids},
      year = {2019},
      volume = {133},
      pages = {187 -196},
      url = {https://doi.org/10.1016/j.jpcs.2019.03.010},
      doi = {https://doi.org/10.1016/j.jpcs.2019.03.010}
    }
    					
    Vos2019b Vos, M. & Winkelmann, A. Effects of multiple elastic and inelastic scattering on energy-resolved contrast in Kikuchi diffraction 2019 New Journal of Physics
    Vol. 21 (12) , pp. 123018  
    article
    Abstract: Energy-resolved Kikuchi patterns for silicon crystals were measured for 30 keV electrons in a reflection geometry. The amount of contrast seen depends strongly on both the geometry and the energy loss. For geometries where the outgoing trajectory is glancing with the surface, the contrast is maximum for zero loss, decreases with larger energy losses and for energy losses over 1 keV, a reversal of the contrast is observed. For geometries where the incoming beam is glancing, the contrast first gradually increases with energy loss and decreases slowly for losses larger than 100 eV. Under these conditions contrast reversal was not seen. These observations are modelled using the cross sections of the various elastic and inelastic processes involved.
    BibTeX:
    @article{Vos2019b,
      author = {M Vos and A Winkelmann},
      title = {Effects of multiple elastic and inelastic scattering on energy-resolved contrast in Kikuchi diffraction},
      journal = {New Journal of Physics},
      publisher = {IOP Publishing},
      year = {2019},
      volume = {21},
      number = {12},
      pages = {123018},
      doi = {https://doi.org/10.1088/1367-2630/ab5cd1}
    }
    					
    Selau2020 Selau, F.F.; Trombini, H.; Marmitt, G.G.; de Andrade, A.M.H.; Morais, J.; Grande, P.L.; Alencar, I.; Vos, M. & Heller, R. Stopping and straggling of 60-250 keV backscattered protons on nanometric Pt films 2020 Phys. Rev. A   article
    Abstract: The stopping power and straggling of backscattered protons on nanometric Pt films were measured at low to medium energies (60--250 keV) using the Medium Energy Ion Scattering (MEIS) technique. The stopping power results are in good agreement with the most recent measurements by Primetzhofer [Phys. Rev. B 86 (2012) 094102] and are well described by the Free Electron Gas (FEG) model at low projectile energies. Nevertheless, the straggling results are strongly underestimated by well-established formulae up to a factor of two. Alternatively, we propose a model for the energy-loss straggling that takes into account the inhomogeneous electron gas response, based on the Electron Loss Function (ELF) of the material, along with bunching effects. This approach yields a remarkable agreement with the experimental data, indicating that the observed enhancement in energy-loss straggling is due to bunching effects in an inhomogeneous electron system. Non-linear effects for the energy-loss straggling are of minor importance.
    BibTeX:
    @article{Selau2020,
      author = {F. F. Selau and H. Trombini and G. G. Marmitt and A. M. H. de Andrade and J. Morais and P. L. Grande and I. Alencar and M. Vos and R. Heller},
      title = {Stopping  and straggling of 60--250 keV backscattered protons on nanometric Pt films},
      journal = {Phys. Rev. A},
      year = {2020}
    }
    					
    Tee2020 Tee, B.P.E.; Kibédi, T.; Lee, B.Q.; Vos, M.; du Rietz, R. & Stuchbery, A.E. Mitchell, A.J.; Pavetich, S. & Koll, D. (Hrsg.) Development of a new database for Auger electron and X-ray spectra 2020 EPJ Web of Conferences
    Vol. 232 , pp. 01006  
    article
    Abstract: An energy correction method is described to account for the Breit and QED effects on Auger electrons and X-ray energies in the recently developed atomic relaxation model BrIccEmis. The results are compared with literature and new experimental data for Z = 52. Overall this improves the agreement of the calculated energies with the literature values. A new atomic radiation database NS_Radlist, will contain atomic transition energies from the BrIccEmis program with these energy corrections.
    BibTeX:
    @article{Tee2020,
      author = {B. P. E. Tee and T. Kibédi and B. Q. Lee and M. Vos and R. du Rietz and A. E. Stuchbery},
      title = {Development of a new database for Auger electron and X-ray spectra},
      journal = {EPJ Web of Conferences},
      publisher = {EDP Sciences},
      year = {2020},
      volume = {232},
      pages = {01006},
      doi = {https://doi.org/10.1051/epjconf/202023201006}
    }
    					
    Tee2020a Tee, B.P.E.; Vos, M.; Trombini, H.; Selau, F.F.; Grande, P.L. & Thomaz, R. The inuence of radiation damage on electrons and ionscattering measurements from PVC 2020 Radiation Physics and Chemistry
    Vol. in press  
    article
    Abstract: Polyvinyl chloride (PVC) is a material that decomposes rapidly when irradiated by charged particles. Here we use energy spectra of electrons reflected from the PVC lms during electron radiation to monitor this process. This is accomplished by measuring the energy distribution of elastically scattered electrons which depends on the mass of the scattering atoms. Incoming electrons with
    energy between 5 and 40 keV are used. Information is obtained about both the relative amount of Cl, C and H present in the sample. Especially the Cl concentration decreases quickly during irradiation. At larger energy losses the signature of the band gap is visible in the energy loss spectrum. The number of excitations within the band gap increases rapidly when the composition of the
    lm changes. The H intensity is somewhat less affected by the electron beam than the Cl intensity but accurate determination of the H content is complicated due to the changing background. Medium-energy ion scattering measurements (using 200 keV protons) and Rutherford backscattering measurements (using 2 MeV He ions) showed a strong decrease in the measured Cl intensity with ion fluence used. The Cl concentration as a function of fluence for electrons, protons and He ions can be described in a uniform way by considering the density of electronic excitations produced under the dierent irradiation conditions.
    BibTeX:
    @article{Tee2020a,
      author = {B.P.E.  Tee and M. Vos and  H.  Trombini and  F.F.  Selau and  P.L. Grande and R. Thomaz},
      title = {The inuence of radiation damage on electrons and ionscattering measurements from PVC},
      journal = {Radiation Physics and Chemistry},
      year = {2020},
      volume = {in press}
    }
    					
    Trombini2020 Trombini, H.; Vos, M.; Reboh, S. & Grande, P.L. Elucidating the capability of electron backscattering for 3D nano-structure determination 2020 Journal of Physics D: Applied Physics
    Vol. 53 (42) , pp. 425103  
    article
    Abstract: Reflection electron energy loss spectroscopy (REELS) is well established for the study of homogeneous materials with flat surfaces. Here we extend the use of this technique to nano-structures consisting of silicon and silica and show that the experimentally-observed peculiar dependence of the REELS spectra on the sample orientation can be reproduced by Monte Carlo simulations using the known sample morphology. A sample with a 3D structure, resembling those found in FinFET transistors, was analyzed through electron Rutherford backscattering (ERBS, revealing the mass of the atoms near the surface) and REELS (revealing the electronic structure). ERBS/REELS spectra were taken at two incoming electron energies (5 and 40 keV) and in two experimental geometries with the component of the outgoing propagation direction along the surface being either parallel or perpendicular to the fins. The measured spectra were different for the two geometries due to attenuation effects within the fins, especially at 5 keV where the inelastic mean free path is of the order of the fin dimensions. This means that the 3D structure induces shadowing effects which suppress the elastic peaks and enhanced the inelastic signal. A Monte Carlo code was used to simulate multiple elastic and inelastic interactions of the electrons with these 3D structures and was indeed able to reproduce these experimental results, including the shadowing effects. A sub-angstrom layer of Au was evaporated on the sample and the changes induced by the Au layer were dependent on the orientation of the fins and were again reproduced by the simulation.
    BibTeX:
    @article{Trombini2020,
      author = {H Trombini and M Vos and S Reboh and P L Grande},
      title = {Elucidating the capability of electron backscattering for 3D nano-structure determination},
      journal = {Journal of Physics D: Applied Physics},
      publisher = {IOP Publishing},
      year = {2020},
      volume = {53},
      number = {42},
      pages = {425103},
      doi = {https://doi.org/10.1088/1361-6463/ab98c2}
    }
    					
    Trombini2020a Trombini, H.; Vos, M.; Marmitt, G.G.; Tee, B.P.E.; Selau, F.F.; de Andrade, A.M.H. & Grande, P.L. The effect of ion implantation on reflection electron energy loss spectroscopy: The case of Au implanted Al films 2020 Journal of Electron Spectroscopy and Related Phenomena
    Vol. 240 , pp. 146935  
    article
    Abstract: Gold-implanted aluminum films are used to investigate how reflection electron energy loss spectra (REELS) change due to the presence of a small concentration of heavy atoms at a specific depth. Au ions were implanted with 30, 100 and 300 keV energy. REELS spectra were taken at energies between 10 and 40 keV. Large changes in the REELS spectra are observed after Au implantation, but the nature of the change indicates that they are not due to modification of the dielectric function of the implanted layer, but should be interpreted as changes in the partial intensities that make up the spectrum. Two models are used to describe the results quantitatively. One method assumes v-shaped trajectories (i.e. only a single elastic deflection) and the REELS spectrum can then be calculated in a closed form. The other method is a Monte-Carlo based simulation which allows for multiple elastic deflections. Both methods describe the experimental spectra quite well, but at larger energy losses significant deviations occur between the measured and calculated intensity for both the implanted and not-implanted films. The difference in the REELS spectrum before and after implantation is less affected by these discrepancies, and can be used to obtain an estimate of both the depth and concentration of the implanted Au atoms. Due to the presence of sharp plasmon features in the energy loss spectrum of aluminum the experiment can tell us directly which partial intensities are affected by the Au impurities, as the recoil energies due to elastic scattering make it possible to identify the contribution of Au to the first few plasmons. As the Au implantation fluence is known the measurement can be used to determine the ratio of the Au and Al elastic scattering cross sections, which deviates strongly from that calculated from the Rutherford formula.
    BibTeX:
    @article{Trombini2020a,
      author = {H. Trombini and M. Vos and G.G. Marmitt and B.P.E. Tee and F.F. Selau and A.M.H. de Andrade and P.L. Grande},
      title = {The effect of ion implantation on reflection electron energy loss spectroscopy: The case of Au implanted Al films},
      journal = {Journal of Electron Spectroscopy and Related Phenomena},
      year = {2020},
      volume = {240},
      pages = {146935},
      doi = {https://doi.org/10.1016/j.elspec.2020.146935}
    }
    					
    Trombini2020b Trombini, H.; Vos, M.; Elliman, R.G. & Grande, P.L. Depth profiling of ion-implanted samples by high-energy electron scattering 2020 Journal of Physics D: Applied Physics
    Vol. 53 (13) , pp. 135304  
    article
    Abstract: For heavy ions implanted in low-Z targets it is possible to determine the depth and concentration of introduced heavy impurities by studying the energy spectra of electrons scattered from the surface. Here, we demonstrate this for the case of 30 and 300 keV Au implantation in SiO2. For high-energy incoming electrons the elastic peak splits up in different components as the recoil losses depends on the mass of the scattering atom. Heavy impurities also affect the partial intensities and hence changes in the shape of the energy loss spectra are observed. These effects are reproduced by a simple model that uses sample composition, atomic elastic scattering cross sections and target dielectric function as input.
    BibTeX:
    @article{Trombini2020b,
      author = {H Trombini and M Vos and R G Elliman and P L Grande},
      title = {Depth profiling of ion-implanted samples by high-energy electron scattering},
      journal = {Journal of Physics D: Applied Physics},
      publisher = {IOP Publishing},
      year = {2020},
      volume = {53},
      number = {13},
      pages = {135304},
      doi = {https://doi.org/10.1088/1361-6463/ab66d8}
    }
    					

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