THEORETICAL-STUDIES OF SURFACE-DIFFUSION - MULTIDIMENSIONAL TST AND EFFECT OF SURFACE VIBRATIONS

We present a theoretical formulation of diffusion process on solid sur face based on multidimensional transition state theory (TST). Surface diffusion of single adatom results from hopping processes on corrugate d potential surface and is affected by surface vibrations of surface a toms. The rate of rare events such as hopping between lattice sites ca n be calculated by transition state theory. In order to include the in teractions of the adatom with surface vibrations, it is assumed that t he coordinates of adatom are coupled to the bath of harmonic oscillato rs whose frequencies are those of surface phonon modes. When nearest n eighbor surface atoms are considered, we can construct Hamiltonians wh ich contain terms for interactions of adatom with surface vibrations f or the well minimum and the saddle point configurations, respectively. The escape rate constants, thus the surface diffusion parameters, are obtained by normal mode analysis of the force constant matrix based o n the Hamiltonian. The analysis is applied to the diffusion coefficien ts of W, Ir, Pt and Ta atoms on the bcc(110) plane of W in the zero-co verage limit. The results of the calculations are encouraging consider ing the limitations of the model considered in the study.