Momentum-space images of surface dimers on GaAs(001)-(2×4) by high-energy Auger and x-ray photoelectron diffraction

Abstract

We have obtained k‐space images of As dimers in the surface layer of GaAs(001)‐c(2×8)/(2×4) from the two‐dimensional intensity maps of high‐energy, core‐level Auger, and x‐ray photoelectron emission. The dimers are revealed as a major splitting in a small‐angle scattering peak that is common to Ga 3d, 3p, 3s, and L3M4,5M4,5 intensity maps. This peak is of a rather complex origin, but the majority component is forward‐focusing of Ga Auger and photoelectron waves generated in the fourth layer by As atoms in the surface layer. The splitting is caused by a change in symmetry in the surface layer resulting from dimer formation. Simple internuclear emitter‐to‐scatterer geometric modeling cannot be used to obtain the dimer bond length from the angles at which the two split‐off features occur. Such modeling, which generates a reasonable quantitative estimate of the surface‐structural parameters when the emitter and scatterer are nearest neighbors, fails in the present case because of the complex origin of this peak. Rather, quantum‐mechanical scattering calculations carried out at either a kinematical or dynamical level are required to extract accurate surface‐structural parameters. Fourier inversions of the angular intensity maps, which are essentially holograms of the surface, do not produce well‐resolved dimer images in real space. This result is due to substantial contributions to the intensity map from emitters other than the one that produces the split peak in k space.