|Ph.D Student||Oleg Weinstein|
|Subject||Faceting during Directional Crystal Growth from the|
|Department||Department of Chemical Engineering||Supervisor||Full Professor Brandon Simon|
In this thesis we present a new approach to modeling the time-dependent evolution of partially faceted melt/crystal interfaces in large-scale melt-growth systems. The method developed involves decoupling between interface motion and thermal field calculations. The interface motion operator is consistent with step-flow and step-source kinetics. The method is shown to capture both nano-scale and macro-scale features of the evolving melt/crystal interface. Rigorous calculation of a number of two-and three-dimensional examples is presented. In these examples the macroscopic shape of the interface and growth velocity are dramatically affected by the type, distribution and dynamics of step sources along the facets. Selected semi-analytical solutions to the interface motion equation are shown to verify numerical calculations.
Modeling of multifaceted 3D systems with different kinetic mechanisms on different facets, as well as the interaction of step sources on a 3D growing facet is also presented and discussed.
The role that surface energy plays in systems with partially faceted melt/crystal interfaces is investigated. For realistic growth rate values, this free energy balance on an advancing circular layer allow to obtain the surface energy-driven undercooling. Results of direct simulation of dislocation step motion are in agreement with this analyze.
Additional simulations show that the dislocation growth rate for small values of undercooling significantly deviates from the growth rate predicted using classical theory. Also, it is shown that the flat-rough interface transition caused by increasing misorientation angle can lead to sharp corner formation or to terracing due to energetic effects.