Development of a four-tip scanning tunneling microscope and study on surface electrical conduction at mamometer scales

点击翻译按钮获取中文摘要

We have developed an independently driven four-tip scanning tunneling microscope in ultrahigh vacuum, which enables four-probe electrical conductivity measurements at nanometer scales.(1) We have measured the electrical resistance of Si(111)-7×7 clean and -√<3>×√<3>-Ag surfaces by changing the probe spacing from 1μm to 1mm. It has turned out that the surface sensitivity in resistance measurements greatly increases by reducing the probe spacing less than 10μm. From the probe-spacing dependence of the resistance, it is found that the 7×7 surface exhibits a three-dimensional electrical conduction, while the √<3>×√<3>-Ag surface has a two-dimensional character.(2) We have devised a 'square-four-point probe method' to detect the anisotropy in two-dimensional conductors, in which the four tips are arranged in square. With this method, we have measured the conductivity of a quasi-one-dimensional metallic surface, Si(111)-4×1-In, revealing that the anisotropy is as large as 70.(3) We have measured the conductance of single carbon nanotubes, by selecting and picking up them by two of the four tips. The results show an interesting feature of conductance.