Development of STM operational in a plasma and its application to a control of plasma materials surface processing on an atomic scale

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In this project, we performed the first attempt at the development of a scanning tunneling microscope (STM) for use under a plasma environment. The apparatus consists of an STM system and a radio-frequency (rf) (430MHz) plasma generation system housed in a vacuum chamber with a rotary pump. A special amplifier with a resolution of 10 femtoamp. up to 1kV is employed for tunneling current measurements. To prevent noise current from the plasma, the Pt-Ir probe tip is coated with epoxy grease and insulated glass using the sol-gel method except around its apex of about 3 mum. Under the conventional glow-plasma condition, the noise current from the plasma was deduced to be less than 0.1 nA during plasma exposure for 1800 sec. Using this apparatus, the step structure on a nanometer scale and atomic image of highly oriented pyrolytic graphite (HOPG) were obtained under rf, low-pressure (0.3 Tbrr) air glow plasma. We also discussed the role of the STM tip for successful, realistic "in situ" observation.