Surface termination of epitaxial NiAl on GaAs(001) by x-ray photoelectron diffraction

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Abstract
The surface termination of molecular‐beam epitaxy (MBE)‐grown NiAl on GaAs(001) has been examined by means of high‐energy x‐ray photoelectron diffraction. Scanned‐angle x‐ray photoelectron diffractionmeasurements of Ni 3p and Al 2pphotoemission intensities were made at select polar and azimuthal angles and compared with single scattering calculations involving different surface terminations. R‐factor analysis was employed to quantify the level of agreement between theory and experiment. Azimuthal angular distributions at shallow polar angles are very similar in appearance for Ni 3p and Al 2pphotoemission intensities. In addition, the R factors are consistently lower for Ni 3pangular distributions when a Ni‐terminated surface is modeled, while an Al‐terminated surface structure yields lower R factors for Al 2p scans. In light of the short range, localized sensitivity of the photoelectron diffraction probe, these results are best understood as evidence for a mixed surface termination. Indeed, R‐factors averaged over the two core levels as a function of composition in the surface layer show broad, shallow minima at intermediate composition for azimuthal scans near grazing emission. This analysis gives strong qualitative support for the presence of a mixed surface termination.

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