Effects of hydrogen on the three-dimensional epitaxial growth of Ni(100), (110), and (111)

The effects of hydrogen on Ni homoepitaxy have been investigated by examini ng rate constants for mobility of Ni during the Ni-growth process with and without the presence of a small amount of hydrogen impurity which is found to act primarily as a catalyst. The rate constant activation energies are d etermined by classical-potential total-energy calculations with semiclassic al zero-point energy corrections for the hydrogen atom. This work extends p revious work in which we have examined the effects of H on submonolayer (tw o-dimensional) Ni(100) growth in Haug, K.; Zhang, Z.; John, D.; Waiters, C. F.; Zehner, D. M.; Plummer, W. E. Phys. Rev. B. 1997, 55, R10233-R10236 an d Haug, K.; Do, N. K. N. Phys. Rev. B. 1999, 60, 11095. We find that fast d iffusion of H atoms occurs on the flat Ni surfaces and the presence of thes e highly mobile H atoms is found to have significant effects on the mobilit y of lone Ni adatoms on Ni(100), but not on the Ni(110) and Ni(lll) surface s. The H atoms are also found to have significant catalytic effects lowerin g the step edge (Ehrlich-Schwoebel descent) barrier and therefore accelerat ing breakdown of three-dimensional Ni islands which form during the epitaxi al growth on the Ni(100) surfaces, and to a very modest extent on the Ni(ll l) sui-face, but this net catalytic effect is not found on the Ni(110) surf aces. While the overall H atom effects on the Ni mobility in these cases ar e primarily catalytic, the kinetically determined Ni island morphologies ma y differ substantially over time periods which are long on the deposition t ime scale, and therefore the morphology differences can become frozen in pl ace.