Application of the scanning tunneling microscope to insulating surfaces

Abstract
We will show the results of experiments in which very thin Au coatings are applied to insulating surfaces to allow the scanning tunneling microscope (STM) to produce topographic images of these surfaces. Results from a variety of materials including fused silica, salt crystals, oxidized metals, silicon, plastic, and a ceramic high-Tc superconductor will be shown. The Au films are made by a low-temperature deposition method which allows for formation of very thin continuous films. Gold coatings are applied in a vacuum system separate from the STM itself. The STM is operated in air or moderate vacuum, thus allowing for rapid and routine sample turnaround. Lateral resolution of ∼10 Å is obtained without the appearance of structure contributed by the Au coatings from 20- to over 100-Å thickness. Good-quality reproducible images of cleavage steps and other features on surfaces are obtained over areas limited by the piezoelectric drive elements.