This award supports Professor Ellen D. Williams and Dr. Raymond Phanuef of the University of Maryland to collaborate with Professor Ernst G. Bauer of the Physics Institute of the Technical University of Clausthal, Federal Republic of Germany, in a study of phase separation of silicon surfaces. At the University of Maryland, a phase separation of surfaces vicinal to Si(111) has been discovered and characterized using Low Energy Electron Diffraction (LEED). A thermodynamical description of the transition has been developed, but major questions about the mechanisms of mass transport remain. At the Technical University of Clausthal, a remarkable new instrument called the Low-Energy Electron Reflection Microscope (LEERM) has been developed. This instrument can be used to image surfaces in real time with better than 200 angstroms resolution. It is currently the only such instrument in the world. Experiments previously performed using LEED at the University of Maryland will be repeated using the LEERM at Clausthal. Silicon surfaces will be imaged at the temperature of the transition so that the motion of the surface steps involved in the phase separation can be observed directly. The results will be used to test theoretical models for step wandering, surface self-diffusion and the energetics of the Si(111) surface reconstruction. Faceting is a widespread phenomenon in which a surface rearranges via large scale mass transport to form planes of different orientations. The occurrence of faceting is important in catalysts, where it is linked to catalyst deactivation and also possibly to oscillations in reaction ranges. Faceting may also cause the smoothness of epitaxial interfaces to be degraded during growth. Finally, the mechanisms of faceting may be important in understanding surface roughness related to adhesion and lubrication. Little progress has been made in developing a detailed understanding of faceting in the past 20 years due to lack of experimental data to support theoretical speculations. This work proposes use of real time imaging to follow surface-faceting under well controlled conditions.
