9704255 Johnson A variable-temperature scanning probe microscope will be installed in an ultra-high-vacuum system that already consists of two growth chambers for molecular beam epitaxy and a surface analysis chamber. One growth chamber is currently used for the heteroepitaxy of fluoride and IV-VI (lead-salt) materials on silicon, while the other growth chamber produces InSb-based heterostructures. Incorporating the requested instrumentation with this growth facility will result in a powerful tool for in situ characterization of surfaces produced during the epitaxial growth of dissimilar materials. This instrument will operate as a scanning tunneling microscope or an atomic force microscope. Samples can be studied at temperatures somewhat higher than the typical growth temperatures and the same region of a sample can imaged every time the sample is transferred from a growth chamber to the microscope. Materials research issues that will be addressed include: the effects of buffer layers in large- mismatch heteroepitaxy; the atomic structure of novel surface reconstructions; mechanisms of alloy ordering and clustering, and dopant incorporation; and the real time progression of strain relaxation for systems with thermal expansion mismatch. Some information derived from the proposed studies will uniquely apply to the material studied, while some effects will be prototypical of many materials. As in the past, improved understanding of such issues will clearly lead to improved heterostructures and devices. In addition to the direct research benefits, acquisition of the instrument will enhance the training of graduate students from several different departments through interdisciplinary research using state-of-the-art facilities. ***