Atomic-resolution scanning tunnelling microscopic images of the 2 x 4 reconstructed surface were presented. These revealed details of the atomic geometry of 2 distinct surface structural phases. When interpreted in terms of the currently accepted dimer vacancy model, these structures corresponded to previously suggested  and  phases that had been identified in reflection high-energy electron diffraction data, and predicted by total-energy calculations. Images of the  phase revealed the position of a localized As dimer non-bonding charge density, relative to an underlying structure which had not previously been observed in scanning tunnelling microscopic studies of that surface. Resolution of the As dimers of the  phase permitted accurate measurements to be made of the relative spacing of the local charge density that was associated with the dimer bonds of this surface.

L.D.Broekman, R.C.G.Leckey, J.D.Riley, A.Stampfl, B.F.Usher, B.A.Sexton: Physical Review B, 1995, 51[24], 17795-9