COMPARISON OF VARIOUS LOW-TEMPERATURE SCANNING TUNNELING MICROSCOPY DESIGNS FOR USE IN SPECTROSCOPY AND TOPOGRAPHY

We report on experiences operating over a dozen scanning tunneling microscopes in liquid helium at 4.2 K over the past four years. The microscopes were both bimorph and tube scanner designs. Most of our scanning tunneling microscopes (STMs) had ceramic frames, but as some of the early models survived only a limited number of thermal cycles (between room temperature and helium temperatures) we also constructed some with metal frames, using titanium. The calibration of the piezoelectric translators at 4.2 K as well as adjustment for the nonorthogonality of the scan directions are discussed. We also discuss various ways we have found satisfactory for the fine approach (tip to sample) in liquid helium. Data obtained with various microscopes are shown.