A. Atrei

Initial stages of oxidation of the Ni3Al alloy: structure and composition of the aluminum oxide overlayer studied by XPS, LEIS and LEED

The oxidation of the Ni3Al alloy was studied by XPS, LEED and LEIS. At pressures of oxygen under approximately 5 × 10−5 Pa and at temperatures higher than approximately 700 K, a layer of Al2O3 grows on the surface forming islands of uniform thickness of the order of 5 A. The structure of these islands is related to that of γ-alumina.

Surface alloying at the SnPt(111) interface: a study by x-ray photoelectron diffraction

Abstract The formation of surface alloys obtained by annealing ultrathin films of Sn deposited on the Pt(111) surface was investigated by low energy electron diffraction and X-ray photoelectron diffraction. The Pt(111)(2 × 2)-Sn and Pt(111)(√3 × √3)R30°-Sn form after deposition of amounts of Sn in the range from 0.2 to 1 ML and subsequent annealing at 1000 K are found by XPD to be single atomic layer surface alloys. Depositing 4–5 ML of Sn and annealing at 400–600 K produces an ordered phase exhibiting a (2 × 2) LEED pattern. This phase is a multilayer surface alloy and it has the same structure as the bulk Pt 3 Sn alloy.

LEED crystallographic investigation of ultrathin films formed by deposition of Sn on the Pt(111) surface

Abstract Deposition of Sn on the Pt(111) surface followed by annealing at 1000 K leads to the formation of ordered phases showing (2 × 2 and ( 3 × 3 ) R 30° LEED patterns, depending on the surface coverage of Sn. Both these phases were studied by LEED dynamical analysis. The best agreement between experimental and calculated I–V curves was obtained by means of models based on the formation of mixed Pt-Sn layers on the surface where Pt and Sn atoms are nearly coplanar with a slight upward buckling of Sn atoms. The structures of these phases are similar to those already observed for the Pt3Sn(111) surface.

Study of the reconstructed (001) surface of the Pt80Co20 alloy

The structure of the clean, (001) oriented single crystal surface of a platinum alloy containing 20 % at of cobalt (‘Pt 80 Co 20 ’) was studied. He + Low Energy Ion Scattering Spectroscopy data indicated that the outermost surface plane of the alloy is composed of virtually pure platinum. Low Energy Electron Diffraction showed a complex pattern which can be interpreted as a c(58 × 22) coincidence unit mesh. A model of the surface can be proposed in terms of a reconstructed surface layer which forms a compact ‘quasi-hexagonal’ plane. The structure and bond lengths in the outermost plane of Pt 80 Co 20 (001) are nearly identical to those of the reconstructed Pt(001) surface.

Epitaxy and alloying at the CoPt(111) interface: a study by X-ray photoelectron diffraction

Abstract Cobalt was deposited on the clean Pt(111) surface at room temperature by thermal evaporation. The overlayer growth mechanism and structure was examined by X-ray photoelectron diffraction, combined with X-ray photoelectron spectroscopy and low energy He+ scattering. During the initial stages of growth cobalt forms a uniform layer of a single atomic layer thickness. Further growth results in the formation of an epitaxial fcc cobalt multilayer. Annealing at moderate temperature causes the formation of a fcc CoPt alloy of variable thickness.

Initial stages of oxidation of the Ni3Al alloy: a study by X-ray photoelectron spectroscopy and low energy He+ scattering

Abstract The oxidation of the Ni 3 Al alloy at low oxygen pressure was studied by low energy He + scattering and X-ray photoelectron spectroscopy. For exposures up to approximately 10 L of oxygen at 900 K the formation of A1 2 O 3 was observed. From a simulation of the relation of XPS and LEISS data for different mechanisms of growth of the oxide overlayer, we show that a linear relation of the LEISS signal to the XPS signal is expected if the layer grows forming islands of uniform thickness. The experimental results indicate that the thickness of the A1 2 O 3 islands is indeed uniform up to the completion of the monolayer. The thickness of the layer was found to be approximately 5 A from an analysis of the XPS results.

Surface composition determination of Pt–Sn alloys by chemical titration with carbon monoxide

The use of chemical titration with carbon monoxide to determine the surface composition of Pt–Sn alloys was studied using Pt3Sn single crystals of known surface composition. The surface composition of the (111) and (100) faces were determined independently by the combination of low‐energy electron diffraction (LEED) crystallography and low‐energy ion scattering (LEIS). CO was adsorbed on these surfaces to saturation at 250 K and thermally desorbed into a mass spectrometer. The area under the thermal desorption spectroscopy curve for the alloy surface was compared to the area under the curve for the pure Pt surface of the same orientation. The ratios were 0.5±0.05 for Pt3Sn(100) and 0.7±0.05 for Pt3Sn(111), in excellent agreement with the 50% Pt and 75% Pt surface compositions derived from LEED and LEIS. The success of the titration method in this case appears to be due to (a) selective adsorption of CO on Pt atoms and (b) the relatively weak effect of the Pt–Sn intermetallic bond on the Pt–CO bonding.

Domain structure, segregation and morphology of the Pt3Sn(111) surface

Abstract Using spot-profile analysis low-energy electron diffraction, we have studied the domain structure and morphology of the Pt3Sn(111) surface after sputtering at room temperature and subsequent anneal treatments which result in the formation of the previously reported ( 3 × 3 ) R30° and (2×2) structures. In addition, we present new results on the temperature-dependent composition of the outermost layer and the subsurface region that is obtained from quantitative analysis of low-energy ion scattering and Auger electron spectroscopy experiments. The combination of these results and previous experiments yields a detailed picture of the evolution of the surface region during the anneal treatments. Finally, we propose the existence of a phase transition at high temperatures between the (2×2) phase and a (2×2)′ phase (not previously observed) on the basis of reversible changes in the SPA–LEED, LEIS and AES data.

Test of structural models for Cu(001)-(√2 × 2√2) R45°-O by LEED intensity analysis

The Cu(001)-(√2 × 2√2)R45°-O structure was investigated by LEED intensity analysis. Several structural models were considered in the calculations. The models proposed on the basis of HREELS results can be ruled out. It was confirmed that the missing row model proposed by Zeng et al gives the best agreement with the experimental data. The structural parameters for this model were refined considering a buckling of the first and second copper layers.

LEED structural analysis of the (001) surface of the ordered fcc Pt3Ti alloy

Abstract The surface structure of the (001) plane of the ordered fcc Pt 3 Ti alloy was studied by dynamical LEED analysis. The model that gives the best theory-experiment agreement corresponds to bulk truncation, with the outermost plane being pure platinum. The results also indicate a contraction of the first interplanar distance with respect to the bulk value and a slight upward buckling of Ti atoms in the second outermost plane.