Nonequilibrium Interface Dynamics:
Theory and Simulation from Atomistic to Continuum Scales

CSIC Building (#406), Seminar Room 4122.
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Equilibrium Morphology and Morphological Transitions

Dr. Ellen Williams

Department of Physics, and Institute for Physical Science and Technology, University of Maryland

Abstract:   As we push materials and device fabrication down to the nanoscale, the atomic characteristics of the component materials are increasingly likely to manifest themselves in the fabrication, properties and stability of the devices. Appropriately designed experimental measurements allow us to address these problems systematically, developing predictive capabilities for materials control. Adaptations of statistical mechanics approaches to measurements on real physical systems, and the application of the results to prediction of thermodynamic and mass transport characteristics at the nanoscale will be presented.

The ability to equilibrate morphological structures will be demonstrated by reviewing the discovery, using diffraction techniques, of reversible transformations of the morphology of surfaces vicinal to Si(111) and equilibrium crystal shape of Pb. The thermodynamics governing the equilibrium structures and the orientational phase diagram will be described in terms of the variation of the surface free energy as a function of the density of steps on the surface. Quantification of the thermodynamic descriptions will be demonstrated by showing how direct imaging measurements (STM, REM, LEEM) have been used to obtain statistical information about the correlation functions of equilibrium step structure, and thus the thermodynamic parameters governing the free energy variation, which are the step stiffness and the step interactions strength. The atomic origins of these free energies, and their use in predicting the orientational stability of surfaces will be presented.

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