SCATTERING INTERFERENCE OF ENERGETIC ELECTRONS ALONG ATOMIC CHAINS - THE EFFECT OF THE ATOMIC ENVIRONMENT

In energetic (> 500 eV) electron scattering along atomic chains the in itial scattering events have a focusing effect, and subsequent events tend to be defocusing. We investigated the degree of forward focusing and the in-depth defocusing for 3-keV electrons along the Ga [110] reg ular chains in the zincblende structure. GaAs, GaP, and GaSb single cr ystals were used, to study the effect of the atomic environment in ter ms of both lattice parameters and partner atoms. Experimentally, the a ngular intensity distribution of elastic and inelastic (losses) Ga Aug er electrons was monitored as a function of the incidence angle, to pr obe the in-depth anisotropy of primary electron-beam intensity. We fou nd that forward focusing is enhanced up to a depth much larger than pr eviously reported, and more than 30 scatterers are necessary to comple tely destroy the intensity anisotropy. Both focusing and defocusing al ong Ga chains are affected by the scattering potential of the partner, V-type atom, being larger in GaP than in GaAs and GaSb. Single scatte ring cluster (SSC) calculations including a broadening of 0.1 eV/Angst rom in the primary beam energy satisfactorily describe the experimenta l findings. However, the progressive narrowing of the zeroth-order for ward feature as the mean depth of origin of the electrons increases is not reproduced by SSC calculations and is possibly ascribable to mult iple scattering.