Multiscale model for epitaxial growth of films: Growth mode transition

Deposition processes often involve surface and fluid-phase phenomena that are inherently coupled but occur over different time and length scales. A multiscale integration hybrid approach, based on domain decomposition, is presented to model such processes. The approach is applied to a model system of physical vapor deposition in a vertical stagnation flow reactor and couples an atomistic stochastic model, solved via a Monte Carlo method, with a continuum model for the fluid phase, solved using a finite-difference scheme. The roles of fluid mechanics, mass transfer, and surface misorientation in the growth process are clarified. It has been found that microscopic surface features such as surface diffusion and surface misorientation affect the growth rate and fluid phase mass transfer mainly at intermediate temperatures. In contrast, the behavior at low temperatures is mainly dictated by mass-transfer limitations in the fluid phase and at high temperatures by partial equilibrium. Surface diffusion decreases the transition temperature from step flow to two-dimensional nucleation, which happens when the fluid transport is uncoupled from the surface, but interestingly it extends the mass-transfer-limited regime to higher surface temperatures.