EFFECT OF SEGREGATION ON PREFERRED SPUTTERING OF ALLOYS

The effects of segregation on the preferred sputtering of alloy surfaces have been analyzed. The top layer of the surface is regarded as behaving differently from the layers beneath the second layer: segregation and dissolution rate constants between the top and second layers are included in the kinetic equations explicitly. It is shown that the fundamental kinetic equations are of a form similar to that developed by Ho, Webb, Carter and Collins, even though the coeffients of the equations are different. The time-dependent solution of the kinetic equations shows that the segregation rate constant plays an important role in the build-up of the steady state. Similarly to the previous result, the altered layer is shown to have a thickness of the diffusion constant divided by the velocity of the recession of the surface. The steady-state compositions at the top and second layers relative to the bulk composition were found to be a function of three parameters: the surface enrichment factor, the diffusion constant divided by the velocity, and the ratio of the yields of atomic removal from the top layer, a correction factor being needed in a particular boundary condition. The existing experimental data on Cu-Ni, Cu-Au and some other alloys are surveyed critically in terms of the results of the theoretical calculation.