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 fabricate 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 than about 50 nm. The surface of the GaAs tip was passivated by sulfur atoms by dipping it into (NH4)(2)S-x and annealing at 400 degrees C. Using the GaAs tip with sulfur passivation, a stable tunneling current was obtained even in air. As a result, a clear atomic arrangement was observed repeatedly in STM imaging of a graphite surface.