Analysis of Al adatoms random hopping on Si(100)-c(4 [formula omitted] 2) surface observed by STM at low temperature: Determination of the hopping barriers

Abstract

Mobility of single aluminium atoms adsorbed on Si(100)-c(4×2) surface was studied by means of scanning tunneling microscopy (STM) at a temperature of 115 K. Due to a strongly anisotropic surface migration along silicon dimer rows the hopping in one-dimensional (1-D) bounded areas of various sizes was observed. Distributions of distances traversed in a time between acquisition of two subsequent STM images were obtained. The experimental conditions were interpreted by a model of 1-D random walk of Al adatoms in areas of limited size with reflective boundaries. Kinetic Monte Carlo (KMC) simulations were used for analysing dependence of a calculated activation energy for a single hop on a size of the 1-D bounded area. The developed method allowed restoration of a real value of the activation energy for the Al adatom hopping in a direction parallel to the silicon dimer rows unaffected by the limited size of the bounded area. The activation energy for hops in a direction perpendicular to the dimer rows was estimated from a distribution of time intervals between individual perpendicular hops.