Ultra-Fine Surface Analysis by a Combined Instrument of an STM and A-P

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The surface study utilizing the unique capability of a scanning tunneling microscope (STM) with atomically high resolution has made us realize that the tunneling characteristics of the STM strongly depend on the structure and composition of the apex of a scanning tip and that the promotion of the surface study with the STM requires the clarification of the tip profile. Then we have realized that an atom-probe (A-P) would be the most suitable instrument for clarifying the apex profile because it can directly image the atomic arrangement and mass analyze individual apex atoms. Accordingly, the outcomes of this research are :(1) Development of a combined instrument of an ultra-high vacuum STM and an A-P.(2) Development of scanning tunneling spectroscopy (STS) to investigate the electronic states of individual surface atoms of surfaces.(3) Installation of a field emission electron spectrometer (FEES) to energy analyze the field emitted electrons from the tip apex. The FEES study successfully demonstrated the variation of the electronic states of metal tip apexes by hydrogen adsorption and a Si cluster of a few atoms.(4) Systematic analysis of the correlation between STM images, STS spectra and the profile of tip apexes. The study clarified that plural apex atoms participating in the electron tunneling generates anomalous ordered STM images and STS spectra varies with the cone angle of the tip apex.The present study suggests that the clarification of the apex profiles is the fundamental requirement for obtaining the reproducible, reliable data with STM and STS. The study is extending over various materials from metals, semiconductors, ceramics to conductive polymers.