M.J. Baldwin (a), J.M. Priest (a), K.E. Prince (b), K.T. Short (b) and M.P. Fewell (a)
(a) Division of Physics and Electronics Engineering, University of New England, Armidale NSW 2351, Australia
(b)Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai NSW 2234, Australia
Samples of AISI 316 stainless steel nitrided by exposure to a low-pressure rf plasma [1,2] have been examined by secondary-ion mass spectrometry (SIMS). The work was carried out on the Cameca IMS 5F magnetic sector secondary-ion mass spectrometer located at the Australian Nuclear Science and Technology Organisation, using a 10 keV Cs beam. The sample was biased at +4.5 kV, resulting in a bombarding energy of 5.5 keV. The primary beam was rastered over areas 250 mm ¥ 250 mm and 100 mm ¥ 100 mm using primary beam currents of 115 nA and 50 nA respectively. Secondary ions were collected from an area 60 mm in diameter centered on the raster pattern.Sputtered atoms were monitored as cluster ions of the relevant species with Cs.
Because of the varying composition of the nitrided layer, it is not clear a priori that the sputter rate is the same in this layer as in the substrate material. We explored this by sputtering for successively increasing times at different, but neighbouring, locations on the sample. The depth of the sputtered craters was measured with a Tencor Alpha-Step stylus profilometer. Figure 1 shows the results: the sputter rate is constant not only across the nitrided layer but also into the bulk material.
Figure 2 shows sputter yields as a function of depth. The nitrogen-containing layer is apparent. There is also evidence that the incoming nitrogen displaces the small proportion of carbon in the alloy. Data such as those in fig. 2 provide a means of examining the effectiveness of the nitriding treatment as treatment conditions are varied. Details will be presented at the Conference.
Fig. 2. Sputter yield as a function of depth for a sample of AISI 316 stainless steel exposed for 3 h at 400 ºC to an rf plasma (13.56 MHz, 300 W) in pure nitrogen at a pressure of 180 mPa and a gas flow rate of 13 mmol s-1 [1,2]. The raster area was 250 mm2.
[1] M.J. Baldwin, G.A. Collins, M.P. Fewell, S.C. Haydon, S. Kumar, K.T. Short and J. Tendys, Jpn. J. Appl. Phys. 36 (1997) 4941-8.
[2] M.J. Baldwin, M.P. Fewell, S.C. Haydon, S. Kumar, G.A. Collins, K.T. Short and J. Tendys, to be published in Surf. Coat. Technol.