An ordered (1×1) structure is formed by evaporating approximately one-half monolayer of Al on GaAs(110) and subsequently annealing at 450°C for 30 min. Both a dynamical analysis of the low-energy electron-diffraction intensities from the resulting half-monolayer of GaAs(110)-$p(1\mathrm{}\times 1)$-Al structure and soft-x-ray photoemission spectroscopy indicate that the Al replaces the Ga in the second atomic layer beneath the surface. The uppermost layer retains the structure of clean GaAs(110) but is relaxed 0.1 Å toward the second AlAs layer.

• Received 14 November 1980

DOI:https://doi.org/10.1103/PhysRevLett.46.440