Controlling activated surface diffusion by external fields

A theory is presented for the diffusion coefficient and the hopping distrib ution of an adatom on a surface in the presence of external fields. Relativ ely simple expressions are derived for the probability of multiple hops in the exponential hopping limit. This limit is the one which is usually found in the diffusion of a metal atom on a metal surface. In this limit the bar rier height (in units of k(B)T) is large compared with the bias created by the field and the energy loss of the particle as it traverses from one barr ier to the next. The hopping distribution is obtained for constant and time varying fields in the adiabatic limit. Typically, the presence of an exter nal field will increase the probability of long hops. The magnitude of the field needed to appreciably increase the probability of multiple hops is 10 (8)-10(9) V m(-1). (C) 1999 Elsevier Science B.V. All rights reserved.