Scanning Tunnel Microscopy Studies of Tetrahedrally Bonded Materials

The Scanning Tunnel Microscope (STM) is a surface analysis tool that has been used to study the geometric and electronic properties of metals, semimetals and semiconductors. Evaporated gold deposited on glass was examined as a preliminary test of the McAllister/RHK STM. Calibration of the STM system was accomplished by imaging annealed pyrolytic graphite (APG), but with surprising results. The peak spacing agreed with the accepted value for STM graphite images of 2.46 A, but the shape of the peaks were often distorted. These distortions can be understood in view of the theoretical work of Kobayashi and Tsukada on the effects of tip orbitals on tunneling images. Surface features of ionized cluster beam (ICB) grown germanium films were examined as a function of cleaning methods, annealing, and film growth under a variety of imaging conditions using two different tunnel microscopes. Cleaning and annealing were both found to reduce the overall roughness of surface features, while island growth was observed to have no apparent dependence on the deposition conditions, except for film thickness.