| This dissertation describes the development of a low temperature tunneling microscope, which combines the two techniques of scanning tunneling microscopy and tunneling spectroscopy.; The recently invented scanning tunneling microscope relies on the quantum-mechanical tunneling of electrons across a several angstrom vacuum gap which separates a conducting tip from a conducting surface. The strong dependence of tunneling current on interelectrode spacing results in a highly localized current. By mechanically scanning the tip, this current can be used to measure surface topography with a lateral resolution approaching atomic dimensions.; The established technique of tunneling spectroscopy also relies on electron tunneling, although in this case between two planar electrodes separated by a solid insulating barrier. The low-temperature current-voltage characteristics of such junctions are found to be rich in spectroscopic information. This information has been successfully related to such diverse physical phenomena as superconductivity of the electrodes, inelastic tunneling associated with molecular vibrations, and resonant tunneling through barrier impurities. Unfortunately, these tunneling spectroscopies all suffer from the weakness that the desired information is spatially averaged over the full size of the junction.; The low temperature tunneling microscopy was developed in order to combine the demonstrated spatial resolution of the scanning tunneling microscope with the powerful technique of tunneling spectroscopy. The resulting instrument allows for the possibility of spectroscopic studies of surfaces with a lateral resolution approaching atomic dimensions.; In developing the low temperature instrument, several room temperature studies were conducted. The exponential dependence of tunneling current on interelectrode spacing was verified. In addition, topographic images were produced which demonstrate a high sensitivity to grain structure.; Capabilities of the new instrument were demonstrated by using it to measure the superconducting character of a noibium-tin surface. Images produced in this manner show strong spatial variations, with reproducible transitions between fully normal and fully superconducting behavior on length scales as short as 13nm. Possible explanations for the observed variations are discussed. |
