The influence of phase-change material composition on amorphous phase stability, crystallization rate, nucleation probability, optical constants and media noise is reported for materials with a growth dominated crystallization mechanism. Two material classes have been studied, doped Sb–Te and doped Sb-based compositions. The material properties of both are greatly influenced by their composition, and in a similar way. For both materials systems hold that the antimony content especially influences the crystallization rate, amorphous phase stability and media noise of the phase-change material. Compositions rich in antimony generally show high crystallization rates, low archival life stability and high media noise. The material properties are further influenced by the presence of dopants like tellurium, germanium, gallium, indium or tin. Germanium and tellurium reduce the crystallization rate, but are essential to increase the amorphous phase stability. Dopants like tin or indium are added to increase the crystallization rate or to adjust the optical constants.

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Surface science models of silica-supported Pt−Co bimetallic catalysts with various Pt/Co ratios have been successfully prepared using the spin-coating technique. Platinum and cobalt loadings on a series of silica-supported model catalysts were quantified by Rutherford backscattering spectrometry. Atomic force microscopy images indicate that flattish layerlike structures were obtained in all cases. The electronic state of Co and Pt was investigated using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows that cobalt is mainly forming octahedrally coordinated Co2+ species in the unreduced catalysts. The formation of the active phase has been investigated by XPS and “in situ” soft X-ray absorption spectroscopy (XAS). The NEXAFS measurements performed under 1−2 mbar of H2 reveal that cobalt is fully reduced to Co0 at relatively low temperature in bimetallic catalysts and reveal a decrease of the electron density of Co as the Pt/(Pt + Co) ratio increases, indicating the formation of alloyed bimetallic particles. This is also supported by XPS measurements. The crotonaldehyde hydrogenation has been studied on planar surface science model catalyst under diffusion-limitation-free conditions in gas phase at atmospheric pressure and temperatures between 100 and 150 °C. The addition of Co significantly improved the selectivity toward crotyl alcohol. This improvement is correlated with the electronic properties of the active phase.

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This article presents results of a study initiated to characterize the plasma-oxidation process of very thin Al films, a technology commonly used to produce good barrier layers for magnetic spin-tunnel junctions. The behavior of oxygen in the oxidizing Al layer is determined using both quantitative (Rutherford backscattering spectrometry, transmission electron microscopy) and qualitative (x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry) analytical techniques. We have applied in situ XPS and experimented with O218 to unravel details of the oxidation mechanism. In addition, the influence of the oxygen pressure on the oxidation rate was established, both with and without a plasma being present. From optical emission spectra it is concluded that this pressure has a minor effect on the relative abundance of excited species in the oxygen plasma. When combined, these data constitute the basis of a model that distinguishes several steps in the plasma oxidation of Al. At the start, oxygen penetrates rapidly throughout the total Al layer, followed by a period of increasing oxygen concentration but constant oxide thickness. Finally, the Co underlayer becomes involved in the oxidation process, which marks the deterioration of the spin-tunnel junction. Evidence is obtained that for the thicker initial Al layers the Co electrode layer starts to oxidize before completion of the Al oxidation. This explains why for 0.8-nm-thick Al films the highest tunnel-magnetoresistance effect is obtained for stoichiometric Al2O3, whereas for 1.5 nm Al this occurs while the oxide is still substoichiometric.

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