Low-energy positron diffraction from GaAs(110)

Intensities of 16 beams of near normal incidence positrons have been measured at T=120 K and analyzed using a multiple scattering model of the low-energy positron diffraction (LEPD) process. Excellent correspondence between the measured and calculated intensities is obtained for a reconstruction that is primarily a bond-length-conserving rotation of the top layer, with As relaxed outward and Ga inward with a tilt angle ω1 = 28.6 ± 3°, confirming the results of previous structure analyses for this surface. The quality of the description of the measured intensities, as measured by the x-ray R factor, is significantly better for LEPD than for low-energy electron diffraction. This result is attributed to the repulsive character of the positron-ion core potential and a resulting more surface sensitive diffraction process for LEPD.