Phase Transitions on Surfaces

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They will conduct an experimental and theoretical study of phase diagrams of vicinal surfaces of Silicon and Germanium. Recent developments in their laboratory imply that faceting associated with reconstructive phase transitions is a general property of vicinal surfaces. This has profound implications for the stability of vicinal surfaces and hence for many advanced device concepts. Faceting associated with reconstruction can be related to the formation of a sharp edge in the equilibrium crystal shape. Using thermodynamic arguments they predict that this kind of behavior is widespread on surfaces that undergo reconstructive phase transitions. They therefore plan to compare the phase diagrams of a number of vicinal Silicon and Germanium surfaces with phenomenological models of the free energy. Universal features of the phase diagrams, such as critical exponents, impose strong restrictions on such models. Nonuniversal aspects, such as phase boundaries, can be used to set limits on microscopic interactions. Simulations of the phase diagrams will test existing models and serve as a guideline for the development of more accurate descriptions. The detailed phase diagrams needed for comparison with the theory will be obtained using their recently developed high-resolution LEED instrument.