H. Isern

Structure of the clean NiAl(1 1 0) surface and the Al2O3/NiAl(1 1 0) interface by measurements of crystal truncation rods

The clean NiAl(1 1 0) surface and the Al2O3/NiAl(1 1 0) interface have been investigated by synchrotron X-ray diffraction experiments. In the case of the oxide surface the analysis of the NiAl(1 1 0) crystal truncation rods (CTR) provide information about the interface between the Al2O3 film and the NiAl substrate. The analysis of the CTR-data shows clearly a rippled Ni-Al topmost surface with an amplitude value of RNi/Al = 0.16 ± 0.01 A for the clean surface and RNi/Al = 0.18 ± 0.02 A for the oxide covered surface. On the clean surface the Al sites are expanded by +3.8\% (outwards) and the Ni sites are contracted by -3.2\% (inwards) respect to the unrelaxed interlayer separation. For the oxide covered surface an increase of the expansion of the outermost Al atoms (+7.3\%) relative to their bulk positions has been found, while the Ni atoms remain (-0.9\%) at the bulk position. On both cases, an ideal surface stoichiometry (1:1) was obtained. However, some intermixing (chemical disorder) of one specimen in the sites of the other and vice versa was present (less than 4\%). This chemical disorder was not enhanced by the presence of the Al2O3 overlayer. Neither rippling nor oscillatory relaxation in deeper layers was detectable.

Combined scanning probe microscopy and x-ray scattering instrument for in situ catalysis investigations

We have developed a new instrument combining a scanning probe microscope (SPM) and an X-ray scattering platform for ambient-pressure catalysis studies. The two instruments are integrated with a flow reactor and an ultra-high vacuum system that can be mounted easily on the diffractometer at a synchrotron end station. This makes it possible to perform SPM and X-ray scattering experiments in the same instrument under identical conditions that are relevant for catalysis.

Magnetic anisotropy of submonolayer Pt films grown on Ni(110)

About one atomic layer of Pt was deposited on a Ni(110) surface to investigate the magnetic anisotropy of the interface. The magnetization of Pt atoms was probed with resonant magnetic x-ray diffraction and the magneto-optical Kerr effect was utilized to probe the average magnetization of the Ni in the near-surface region. Our results show that the magnetization of the Pt atoms in the surface plane depends on the direction of the applied field. While the [10] direction shows a hysteresis cycle of the Pt film typical of an easy magnetization axis, the [001] direction has a hard axis behaviour. In contrast, the Ni(110) substrate shows similar cycles for the two directions. A possible explanation, based on the formation of an anisotropic superstructure, as observed by means of surface x-ray diffraction, is suggested.