Surface x-ray-diffraction measurements have been done in cobalt ultrathin films (2–12 atomic layers) grown on Pt(111). Cobalt grows, at room temperature, in an imperfect layer-by-layer mode with its own lateral lattice spacing. The packing of the atomic planes is predominantly fcc but it changes to hcp upon annealing to $\sim 450\mathrm{K}.$ Further annealing to $\sim 550\mathrm{K}$ results in alloying. Several alloys have been identified with stoichiometries close to the bulk stable phases. Resonant magnetic diffraction experiments in the $L_{\mathrm{III}}$ absorption edge of Pt allow one to determine the magnetism of the Pt atoms at the interface. By measuring magnetic crystal truncation rods, it has been found that only the Pt atoms in contact with the Co overlayer are magnetized $\left(\sim 0.2{\mu }_B\right)$ being the magnetization of the second Pt layer about ten times smaller. The induced magnetic moment of the Pt interface has been found to depend rather linearly on the thickness of the Co film, similarly to the magnetization of the overlayer. The transformation fcc to hcp of the cobalt stacking results in a ∼25% enhancement of the magnetization at the interface.

The $c(4\times 2)$ reconstruction of Ge(001) has been studied by x-ray diffraction of 150 K by measuring in-plane reflections and out-of-plane intensities of fractional order rods. The structure consists of an alternate arrangement of buckled dimers (tilt angle ${19}^{\circ }\mp 1^{\circ }$) along the [110] and [ $1\overline{1}0$] surface directions. The dimer rows are not straight along the [110] direction but show a slight zigzag with an amplitude of $0.340\mp 0.005$ Å.

We have investigated the effect of In on the homoepitaxial growth of Cu(100) by surface x-ray diffraction. We show that In enhances the interlayer transport by lowering the barrier for interlayer diffusion (Schwoebel barrier) at step edges. This effect is most pronounced for growth at low temperatures or when In is annealed on the surface before Cu deposition is started. Enhanced island nucleation cannot explain the smoother growth. The results are in agreement with recent calculations. We speculate that In also has a neutralizing effect on contaminants or defects.

Surface magnetic x-ray diffraction experiments have been done on the (111) surface of the ferromagnetic alloy C${\mathrm{o}}_3$Pt. This has been achieved by tuning the photon energy to the $L_{\mathrm{III}}$ absorption edge of Pt in order to benefit from the increased magnetic cross section at resonance. Analysis of the data reveals that the magnetism of the Pt atoms on the first atomic layer is smaller by about a factor of 2 than that of the Pt atoms in the bulk, the reason probably being the reduced Co concentration at the surface.