Elemental Analysis for Scanning Tunneling Microscope by using X-ray Induced Tunneling Current (Development of Elemental Analysis STM)

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We developed ultra-high vacuum STM equipment, and installed to Synchrotron radiation facility in Tsukuba. Sample chamber was placed on X-Y-Z stage. X-Ray beam (1 x 0.04 mm) irradiated the surface at small incident angles. First, adjustment of sample position was performed. When the x-rays irradiated the sample in the correct way, the STM tip current increases. Therefore, we adjusted the sample position by monitoring this STM tip current. Then, sample cumber was evacuated by rotary pump and turbo-molecular pump. Finally, these pumps were stopped and ion pump was used.Layered samples such as Au (or Ni)- Pt-Si wafer were measured. When the vacuum evaporation of Au, small particles were used as mask, as a result, Au layer with small holes was obtained. This sample is useful to evaluate lateral resolution.When X-rays irradiate the sample, the STM tip current is observed. This current was too small even if synchrotron radiation was applied, several pA. The STM images with and without x-ray irradiation were compared each other. However, clear difference was not observed. The tunneling current was about 0.5 nA, which was considerably larger than x-ray induced STM tip current. We recognized several points that should be improved for the experiments at the Synchrotron radiation facility. We intend to continue this experiment.