IMPURITY SEGREGATION IN LENNARD-JONES A/AB HETEROSTRUCTURES .1. THE EFFECT OF LATTICE STRAIN

The solidification kinetics of Lennard-Jones heterostructures are investigated using nonequilibrium molecular dynamics computer simulation techniques. The heterostructures are of the form A/A1-xBx. In this paper, the nature of the A and B atoms comprising the alloy differ only in size, the B atoms being 10% larger than the A atoms. The segregation of the solute B atoms from the solid into both a surface-melted thin film (wetting the solid-vapor interface) and into a bulk-liquid phase following energy input from a simulated laser pulse is studied. The segregation of the (impurity) B atoms into the liquid is found to be enhanced at the (111) orientation when the A B alloy is under strain, but enhanced on the (100) orientation when the alloy is strain free. Comparison to the solute redistribution theories of Aziz (the continuous growth model) and of Jackson, Gilmer, and Leamy shows good agreement with the simulation-derived segregation coefficients in most cases. The periodic stepwise growth model of Aziz is found to give less accurate values of the segregation coefficient. Although the evidence is not conclusive, the simulation results tend to favor a physical picture for solute redistribution in which the solute and substrate do not crystallize at the same rate.