AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA7
Water Enhanced Decomposition and Nanometer Scale Structure Formation Generated by Radiative Exposure of Solid Surfaces

Monday, November 3, 2003, 4:00 pm, Room 326

Session: Stimulated Processes at Surfaces
Presenter: K. Nwe, Washington State University
Authors: K. Nwe, Washington State University
S.C. Langford, Washington State University
J.T. Dickinson, Washington State University
Correspondent: Click to Email
Novel nanometer scale structures on insulating inorganic materials with wide bandgaps can be generated by simultaneous exposure of surfaces to electron and laser beams plus low pressure water vapor. Dramatic synergisms are observed on ionic single crystal surfaces due to bond weakening which arises from localized chemisorption. We are able to modify single crystal surfaces of alkali halides and calcium phosphates/carbonates either at the single atomic layer level or, with higher intensities, at the level of several microns. These modifications are due to electronic excitations leading to decomposition of the crystal. Arrays of cones and fractal structures with unique optical properties can readily be generated. Alkali halide and nitrate surfaces exhibit strongly angular dependent “black” surfaces which are generated in a self-organized fashion. The high absorption is due to the high tortuosity of the surface (a “stealth” surface). We also quantify that in the presence of water vapor, the rates of both laser and electron beam induced decomposition/desorption increase by as much as an order of magnitude. We present AFM evidence that this is a highly localized, defect mediated mechanism. We suggest that point defect clusters lead to atomic dimension step structures (e.g., kinks) that peel off due to bond weakening from sorbed water derived radicals. Supporting evidence from spectroscopic and microscopic data on exposed surfaces will be presented.