Development of nano-scale processing with the tunneling electrons from a scanning tunneling microscope (STM) under atmospheric or reduced pressure

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A semi in-situ processing system was developed. It consists of a STM system, CVD chamber with a turbo molecular pump (TMP)(vacuumed below 10^<-7> Torr), a vibration isolator, Ta-filament and gas inlet system for CVD, and a substrate guiding system using a micrometer head. The STM system and the CVD system are separated by an AIN-BN thermal barrier. The substrate guiding system makes HOPG substrates go back and forth between the STM system and the CVD system. Since it can be adjusted to about 1mum, STM observations of same areas on nanometer scale can be performed successfully.Moreover, we examined the cleaved highly oriented pyrolytic graphite (HOPG) as substrates for nano-processing of diamond films. It is well-known that the large atomically flat and inert surface can be easily obtained. What was more fortunate, diamond films can be synthesized on a HOPG substrate.We tried semi in-situ observations of nanometer scale structures deposited by filamentassisted CVD of CH_4-H_2 system. Typical experimental conditions are as follows: gases, CH_4 + H_2(H_2/CH_4=49.5sccm/0.5sccm); total pressure, 50Torr; Ta-filament temperature, 1800 - 2300K; substrate, HOPG at room temperature; deposition time, 10sec. From the STM images before and after deposition, deposits about 10 to 100nm could be observed. Most of them were deposited along the natural steps of a HOPG substrate.Further researches at higher substrate and filament temperatures, where the nucleation of diamond is expected, are now in progress. In addition, using the surface modifications with using a STM, nano-processing of diamond films will have been developed.