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

利用具有原子高分辨率的扫描隧道显微镜（STM）的独特能力进行的表面研究使我们认识到STM的隧道特性强烈依赖于扫描尖端的结构和组成，并且利用STM促进表面研究需要澄清尖端轮廓。然后我们认识到原子探针（A-P）可以直接成像原子排列并对单个顶点原子进行质量分析，是澄清顶点轮廓最合适的仪器。因此，本研究的成果是：(1)研制了超高真空STM和a- p的组合仪器。(2)发展扫描隧道光谱（STS）来研究表面单个表面原子的电子态。(3)安装场发射电子能谱仪（FEES），对从尖端发射的场电子进行能量分析。FEES研究成功地证明了氢吸附和少量原子的Si簇对金属尖端顶点电子态的影响。(4)系统分析STM图像、STS光谱与尖端轮廓的相关性。研究表明，参与电子隧穿的多端原子产生了异常有序的STM图像，STS光谱随尖端锥角的变化而变化。本研究表明，澄清顶点剖面是获得可重复、可靠的STM和STS数据的基本要求。这项研究正在扩展到从金属、半导体、陶瓷到导电聚合物等各种材料。

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.