INDUSTRIAL UNIVERSITY COOPERATION: Surface and Thin Film Investigations With Low Energy Positrons

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The structural, electronic, and magnetic properties of thin metal films and metallic and semiconductor surfaces will be investigated with a new ultra-high vacuum, low energy beam of spin-polarized positrons. Two principal techniques will be employed: energy and angle resolved spectroscopy of positrons re-emitted from surfaces; and surface electron capture by (spin- polarized) positrons to form positronium. The electronic properties (positron work function, electronic exitations, and mean free paths) and magnetic properties (surface critical exponents and anisotropies) will be studied as a function of film thickness and substrate composition as the film evolves from 2- dimensional to 3-dimensional character. Both techniques are also sensitive to trapping of positrons at surface and near surface defects and thus structural properties (surface roughness, island formation, nucleation densities, interface interdiffusion) of supported thin films can be studied as well. Ultimately, the goal is to incorporate the above techniques into a scanning positron microprobe to allow imaged spatial resolution of thin film and surface phenomena below 1 micron. Thin films and surfaces exhibit properties that can be distinctly different from a material's bulk properties. Such differences can produce great technological opportunities in such diverse areas as chemical catalysis, magnetic films, and tribological coatings.