SURFACE ELECTRONIC TRANSPORT

(1)我们建立了一台超高真空扫描电子显微镜-分子束外延装置，其中安装了丹麦技术大学研制的微型四探针（探针间距为8μ m）系统。利用该系统，我们借助显微镜测量了目标表面区域的电导率。(2)我们发现Si（111）-Ag ~ 3× Ag ~ 3表面的电导比Si（111）-Ag ~ 7清洁表面的电导高两个数量级。这是因为测量由于小的探针间距而变得表面敏感，从而直接检测相应表面的固有特性。(3)通过将微型四探针沿样品表面沿着移动，发现台阶上和台阶间的表面电导有很大差异。这直接意味着表面载流子被表面原子台阶散射，导致电导降低。(4)我们已经做了计算机模拟，使用二维电阻网络获得的样品的表面电导图从测量的电导图。(5)将丹麦技术大学最新研制的纳米四探针（探针间距0.5μm）安装在上述显微镜上，用于表面电导率的测量。

(1) We have constructed an ultrahigh-vacuum scanning electron microscope-molecular beam epitaxy apparatus, in which a micro-four point probe (with 8μm-probe spacing) system, which has been developed in Denmark Technical University, has been installed. With this system, we measured electrical conductance of aimed surface areas with aid of the microscope.(2) We have found that the electrical conductance of a Si(111)-√3×√3-Ag surface is higher than that of a Si(111)-7×7 clean surface by two orders of magnitude. This is because the measurements become surface-sensitive due to the small probe spacing so that the intrinsic properties of the respective surfaces are directly detected.(3) By shifting the micro-four point probe along the sample surface, we have found that the surface conductance is quite different between on terraces and across step bands. This directly means that the surface carriers are scattered by surface atomic steps, causing the reduction in conductance.(4) We have done computer simulations using two-dimensional resistors networks to obtain the surface conductance maps of a sample from the measured conductance maps.(5) A nano-four point probe (0.5μm probe spacing), which has been newly devised in Denmark Technical University, has been installed in the above-mentioned microscope, and used for surface conductivity measurements.