Scanning Tunneling Microscope Tip-Sample Interactions: Atomic Modification of Si and Nanometer Si Schottky Diodes

Abstract

In the first part of this article, tip-sample interactions and their use to modify surfaces at the atomic scale are discussed. In particular, a chemically assisted field-evaporation/desorption process, as a general method for breaking strong chemical bonds and inducing atom-transfer, is discussed. This capability is demonstrated using the atomic-scale modification of Si(lll). It is further proposed that, due to the elastic coupling between surface atoms, there is a material-dependent limit to how small and how local a scanning tunneling microscope (STM)-induced modification can be. Evidence for large-scale restructuring as a result of “local” modification of the Au(111)-22x √3 surface is presented. The properties of the actual nanometer-size contacts of metal tips with Au, Si(111)-7x7, and Si(100)-2x 1 surfaces, and model nanostructures composed of Si epitaxial islands are then considered. The objective is to investigate the behavior of a simple electronic device, the Schottky diode, at the extreme limit of miniaturization. The resistance of the nanometer contacts is found to be a strong function of the semiconductor surface reconstruction, exposure to gases, and subsurface doping changes. The electrical characteristics of the nanometer diodes are very different from those predicted by extrapolation of the behavior of macroscopic devices. These experiments indicate that the STM can be a powerful tool for probing local electrical properties via tip-sample point contacts. © 1993, American Vacuum Society. All rights reserved.