Photoelectron diffraction determination of the structure of the Cu(100)c(2x2)-Mn surface phase

The structure of the Cu(100)c(2x2)-Mn surface phase has been determined using scanned-energy mode photoelectron diffraction (PhD) from the Mn 2p(3/2) core level. The results confirm the earlier finding of a quantitative LEED study, namely that the surface layer comprises an ordered, strongly corrugated two-dimensional alloy in which the Mn atoms occupy substitutional sites. By using near-grazing as well as near-normal emission directions, the PhD data are found to be sensitive to the locations of both the alloy (approximately coplanar) and the underlying substrate Cu atoms relative to the Mn emitter. This can be seen both in direct 'projection method' data inversion maps of the emitter environment and in full multiple-scattering simulations. The PhD data indicate a large outward relaxation of the Mn atoms relative to the surrounding alloy-layer Cu atoms (0.39+/-0.08 Angstrom), but this is consistent with the previous LEED study within the quoted precisions. There are, however, statistically significant differences between the LEED and PhD conclusions regarding some of the structural parameter values, most notably the layer spacing of the Mn atoms to the underlying pure Cu substrate layer.