*Kazuo Terashima, Yoshimasa Taniguchi, Kiyoyasu Tachibana, and Toyonobu Yoshida

Course of Metallurgy and Materials Science, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-8656, Japan
*kazuo@plasma.mm.u-tokyo.ac.jp

Nowadays, in plasma film processings, plasma surface interaction has received a lot of interest and become one of the most important topics. Therefore, development of surface analyses on nanometer-scale under plasma atmospheres have been highly expected. However, there have been almost no reports on this as yet. On the other hand, the scanning tunneling microscope (STM) is well known to be a powerful local probe capable of imaging and measureing physical/chemical properties and manipulating matter down to the atomic scale in almost any environments: e.g., in gas, in liquid and under vacuum conditions, except in plasma.

In this study, we developed an STM apparatus operating under plasma environments for the firtst time. It consisted of an STM system and a radio-frequency (440MHz) plasma generation system housed in a vacuum chamber with a rotary pomp. A special V-I converter with a resolution of 10 f-amp up to 1kV was employed for a tunneling current measurement. Moreover, in order to prevent a noise current from a plasma, a Pt-Ir probe tip surface exposed to a plasma was reduced to a very small area at the tip end, applying an insulating glass coating to tips by sol-gel method. The uncovered part extended by several mm from the tip end. In our glow-plasma, the noise current could be reduced to be several hundred pico-ampere. Using this system, the nanoscale step and the atomic image of highly oriented pyrolytic graphite (HOPG) as a standard sample could be successfully obtained under radio-frequency low-pressure (0.3 Torr) glow plasma. To our knowledge, this is the first surface atomic image under plasma environments. We hope that our study opens up a new method and field in plasma diagnostics for a solid surface under a plasma, in other words, an interface between a plasma and a solid surface.