Preparation of Atomically Smooth Germanium Substrates for Infrared Spectroscopic and Scanning Probe Microscopic Characterization of Organic Monolayers

The suitability of antimony-doped germanium crystals for use as infrared attenuated total reflection wave guides and conducting substrates for scanning tunneling microscopic imaging of absorbed organic monolayers has been evaluated. We have used repetitive ion bombardment followed by resistive heating of a germanium crystal under ultrahigh vacuum conditions to produce large, atomically flat regions on a Ge(111) crystal face. Through the combined use of STM, Auger spectroscopy and low-energy electron diffraction, we have demonstrated that monolayer quantities of tellurium electrochemically deposited onto the Ge surface dramatically reduce the rate of surface oxidation and permit the use of germanium crystals as STM substrates in air. The first STM images acquired in air with Ge as the conductive substrate are reported. No degradation of IR spectral quality occurs when using the Te-covered, Sb-doped Ge crystals as ATR elements. These findings suggest that Te-coated, atomically flat, low-resistivity Ge substrates are suitable for both IR spectroscopic and STM imaging of organic monomolecular films.