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We have measured the polar scans from a cubic GaN(001) single crystal by X-ray photoelectron diffraction (XPD) with high angular resolution. The intensities were recorded within (100), (110) and (110) substrate planes from Mg Ka excited N 1s and Ga 3d core levels. The data reveal unexpected shapes in forward focusing peaks for the N is XPD patterns. Along [001] and [111] directions a large splitting in the structures is observed. The observed patterns are reproduced very well by a multiple scattering spherical wave cluster calculation but the single scattering approach is sufficient to qualitatively explain the remarkable features in the N Is profiles. In particular we demonstrate that the splitting of the structures along some low index crystallographic directions is caused by the predominance of interference phenomena due to atoms located in specific positions close to the dense atomic chains. As a result of the smaller forward scattering amplitude of the N atoms as compared to that of the Ga atoms, the interference effects are strongly reinforced when there are Ga atoms close to N atomic chains. In the Ga 3d XPD patterns these interference effects also appear but forward scattering still prevails along low index directions.

Mn films with a thickness of 2–15 monolayers (ML) have been deposited, in ultra-high vacuum, on a Ag(001) single crystal and analyzed by low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD). When a 12 ML film is deposited at room temperature (RT), a ∼3 ML-thick diffuse interface is formed, and Ag segregation occurs on top of an epitaxial body centered tetragonal (bct) Mn layer. If the same amount of Mn is deposited at 80 K in order to block interdiffusion, the film grows in a polycrystalline α-Mn phase. Annealing the sample at 300 K does not markedly change its structure. However, when a 3 ML template of Mn is first deposited on the substrate kept at 80 K, and then 9 ML at 300 K, the data show that the film is pseudomorphic and adopts an epitaxial bct phase, and that the system exhibits an abrupt interface.

Thin Cu layers have been evaporated at room temperature on Cr films (~ 10 monolayers) deposited on a Cu(001) single crystal. The Crystallographic structure of these sandwiches is analysed by means of low-energy electron diffraction (LEED), angle-resolved ultra-violet photoemission spectroscopy (ARUPS) and X-ray photoemission spectroscopy. The data show that the attenuation of the Cr signal versus Cu deposition is much lower than expected for a uniform film growth. Moreover, the LEED pattern characteristic of the Cr film (made of Cr(110) domains with four different orientations) is visible for Cu coverages as high as 23 ML. This indicates a strong diffusion of the Cu atoms on the Cr film surface and the formation of Cu three-dimensional islands which present, according to ARUPS and X-ray photoelectron diffraction measurements, a highly disordered fcc Crystallographic structure. However the low reactivity of the sandwiches towards oxygen suggests that the whole Cr surface is wetted by at least 1 ML of Cu.

Thin Cr films (∼20 A) deposited in vacuum at 300 K on a Cu(001) single crystal have been annealed at various temperatures and analyzed by angle resolved ultraviolet photoemission, X-ray photoemission, X-ray photoelectron diffraction and low energy electron diffraction. The data show that Cu segregation occurs above 425 K, resulting in an atomic monolayer wetting the whole Cr film. At 775 K, the Cr overlayer collapses and the Cu(001) substrate surface becomes partly uncovered.

We have investigated the crystallographic structure of ultra-thin Mn films deposited at room temperature on a clean Ag(100) single crystal, using angle-resolved ultra-violet photoemission, X-ray photoelectron diffraction (XPD) and low-energy electron diffraction. The evolution of the Ag 4d valence band shows deviations from simple layer by layer growth. These results, combined with the XPD data, indicate that by ∼1–1.5 monolayers of Mn a two layers thick Mn-rich epitaxial MnAg alloy is formed that continues the face centered cubic lattice of the Ag substrate.