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Thurs., Feb. 2, 2012
10:45 a.m., NSERL 3.204








"Toward a Quantitative Continuum Model for Irradiation-Induced Morphology Evolution"
Scott A. Norris, Southern Methodist University, Dallas

Despite more than 40 years of research since the first observation of patterns on ion-irradiated surfaces, a predictive model for the formation and selection of these patterns has remained elusive -- physically-derived models based on the underlying assumptions of Bradley-Harper theory [1] have been unable to explain many observed phenomena, whereas more generic phenomenological models have relied on the use of fitting parameters to obtain experimental agreement.

In this talk, we discuss recent progress in both the prompt impact-driven regime and the gradual energy-relaxation regime that offers the promise of a quantitative, physically-derived model that agrees with recent experiments on Si, without the use of fitting parameters. For the prompt regime, angle-dependent crater-function measurements obtained using MD are upscaled directly into continuum PDE terms, revealing that the prompt regime is dominated by redistribution, and that good agreement with experiment is possible neglecting curvature-dependent erosion entirely [2]. For the gradual relaxation dynamics, Umbach's model of the amorphous film as a viscous fluid [3] is augmented with a physical model of beam-induced biaxial stress, producing reasonable agreement with experimentally-observed steady film stress and ripple propagation direction.

We will show that this combination of prompt- and gradual-regime models offers improved agreement with many of the experimental observations associated with nearly flat surfaces in the linear regime.

Prof. Scott Norris received his Ph.D. in Applied Mathematics from Northwestern University in 2006, and then served as a Lecturer of Applied Mathematics at Harvard university from 2007-2010, supported by an NSF Mathematical Sciences Postdoctoral Research Fellowship. In the Fall of 2010 he joined the faculty of the SMU Mathematics department.

Prof. Norris's research focuses mainly on problems in materials science at the nano-scale, particularly those involving surface modification and morphology evolution. He has studied the growth of faceted crystal interfaces, the shape of silicon nanowires grown via the vapor-liquid-solid mechanism, and the spontaneous formation of patterns on semiconductors irradiated with ion beams. These problems are all examples of highly non-equilibrium evolution driven primarily by surface physics.