Samples with orientations which were vicinal to (2 5 11) to within 1° were prepared by molecular beam epitaxy and were analyzed in situ by means of scanning tunnelling microscopy, low-energy electron diffraction and reflection high-energy electron diffraction. First-principles electronic structure calculations were also carried out. The (2 5 11) surface was stable, and its orientation was located within the stereographic triangle. Under a wide range of As-rich conditions, a (1 x 1) reconstruction formed which was characterized by an inclined series of three As dimers and which satisfied the electron counting rule. The terrace size was limited only by the macroscopic off-orientation of the samples. The surface was perturbed by thin stripes of the nearby orientation: (3 7 15). The dangling-bond densities of (2 5 11) and (3 7 15) were almost equal, but (3 7 15) violated the electron counting rule. An analysis of this perturbation suggested that, in general (for semiconductor surfaces), the gain in stability which arose from minimization of the number of dangling bonds was significantly greater than the gain which arose from reaching a semiconducting ground-state. Upon annealing the samples under ultra-high vacuum, a fairly rough surface structure developed whose mean orientation was different from (2 5 11).

Surface Structure of GaAs(2 5 11). L.Geelhaar, Y.Temko, J.Márquez, P.Kratzer, K.Jacobi: Physical Review B, 2002, 65[15], 155308 (13pp)