FABRICATION OF GAAS MICROTIPS FOR SCANNING-TUNNELING-MICROSCOPY BY WET ETCHING

GaAs semiconducting microtips for scanning tunneling microscopy (STM) were fabricated by a wet etching method. A solution of H3PO4-H2O2-H2O (10:1:1) and an etching temperature of 5 degrees C were chosen to fabr icate a sharp GaAs point. The apex of the GaAs tip was constructed of four (150) facets, and the radius of curvature at the top was less tha n about 50 nm. The surface of the GaAs tip was passivated by sulfur at oms by dipping it into (NH4)(2)S-x and annealing at 400 degrees C. Usi ng the GaAs tip with sulfur passivation, a stable tunneling current wa s obtained even in air. As a result, a clear atomic arrangement was ob served repeatedly in STM imaging of a graphite surface.