d and f metal interface formation on silicon

Electronic and geometric structure in silver clusters

Cs and O adsorption on Si(100)2 x 1: A model system for promoted oxidation of semiconductors.

We present new experimental results from a comprehensive study of the chemisorption of oxygen on differently prepared Si(111) surfaces, using low-energy electron diffraction and high-resolution electron spectroscopies such as x-ray photoemission spectroscopy, x-ray-initiated Auger-electron spectroscopy, and polarization-dependent ultraviolet photoemission spectroscopy. In the monolayer regime two different states of oxygen have been observed: a molecular precursor and a stable dissociated configuration. The latter is the subject of this paper. Its electronic structure and local symmetry are compatible only with a bridge-bonded atom between Si atoms in the first and second layer, respectively, with relatively little influence on the dangling bonds. The presence of a second dissociated oxygen adsorbate, e.g., a diatomiclike monoxide, is excluded by our data. The coverage dependent O 1s and Si 2p data indicate that the observed satellite structures in the submonolayer regime are due to excitations rather than to chemically shifted peaks from atoms in different bonding situations.

Initial stages of oxygen adsorption on Si(111): The stable state.

In the initial stage of oxygen adsorption on Si(111) surfaces, a metastable molecular state is found which precedes dissociation and insertion of oxygen atoms in bridging positions between first- and second-layer silicon atoms. This precursor can be observed in conventional photoemission experiments at low coverages and\char22{}for optimum retention\char22{}at low substrate temperatures. Combining the results from several high-resolution electron spectroscopies such as x-ray photoemission (XPS), polarization- and photon-energy-dependent uv photoemission, x-ray-induced Auger spectroscopy, and near-edge x-ray absorption, we are able to characterize the precursor as a negatively charged molecular species chemisorbed in a bridge configuration between dangling bonds of the surface. Its decay and conversion into the stable dissociated state could be monitored by XPS up to room temperature, showing a thermally or electronically activated behavior. For the reaction of ${\mathrm{O}}_{2}$ with Si(111), a two-stage adsorption model is proposed. It explains a number of observations and features of oxygen adsorption on differently prepared Si(111) surfaces. The present model may be applicable to other semiconductor surfaces as well.

Initial stages of oxygen adsorption on Si(111). II. The molecular precursor.

We examine the effect of thin (1--2 monolayers) overlayers of the low-electronegativity metals Cs and Na upon the oxidation of Si(111) surfaces. Synchrotron-radiation photoemission studies of oxygen chemisorption as a function of overlayer thickness and oxygen exposure indicate large oxidation-promotion effects and the formation of Si oxide phases where high Si oxidation states dominate. Comparison with promotion effects induced by transition-metal and noble-metal overlayers forces, for alkali metals, a reevaluation of the microscopic mechanisms proposed to explain overlayer-induced oxidation promotion.

Electronic promoters and semiconductor oxidation: Alkali metals on Si(111) surfaces.

Hg1−xMnxTe alloys have been proposed as a suitable alternate material to mercury–cadmium–telluride for infrared applications. We report synchrotron radiation photoemission studies of the electronic structure of such alloys for x≤0.15. Valence band resonant photoemission was exploited to probe the valence states, while high resolution core photoemission yielded information on bonding stability and ionicity. The results are compared with those obtained for Hg1−xCdxTe and for HgTe. The Mn bonding in Hg1−xMnxTe appears mostly due to the coupling of metal‐s states with Te p‐states, with limited evidence of d–p hybridization. The ionicity of the Hg–Te bond is not substantially modified in the ternary alloy relative to HgTe, while for Hg1−xCdxTe we directly observe dramatic destabilization of the Hg–Te bond. Correspondingly, Hg1−xMnxTe should exhibit lattice surface and interface stability similar to those of the binary parent compound and largely exceeding those of Hg1−xCdxTe.

New ternary semiconductors for infrared applications: Hg1−x MnxTe

: Thin mixed valence overlayers (1 monolayer) of Sm deposited on Si or GaAs cleavage surfaces prior to oxygen exposure give rise to oxidation promotion effects of unprecedented magnitude. In contrast with this, purely divalent Sm overlayers (thickness 1 monolayer) exhibit negligible oxidation promotion activity. We examine the role of metal electronegativity and metal-semiconductor interface morphology in determining the specific catalytic activity of the overlayer.

Low-electronegativity overlayers and enhanced semiconductor oxidation: Sm on Si(111) and GaAs(110) surfaces

We present bremsstrahlung-isochromat-spectroscopy and synchrotron-radiation photoemission-spectroscopy studies of CdTe single crystals cleaved in situ. The photoemission data, and empirical-pseudopotential calculations of the band structure, were used to reevaluate the position of valence and core spectral features. The bremsstrahlung-isochromat-spectroscopy results emphasize structure in the conduction-band density of states at 4.1, 6.7, 9.6, 11.3, 12.5, and 15 eV above the valence-band maximum. The calculations are found to reproduce the conduction-band structure throughout a range of 18 eV above the valence-band maximum.

Electron density of states of CdTe.

On presente une etude de photoemission de radiation synchrotron de la chimisorption sur des surfaces de GaAs(110) lies in situ. On analyse l'emission de la bande de valence et la photoemission de cœur a haute resolution en fonction de la couverture d'hydrogene et de l'intensite de fuite photoelectronique. On montre qu'au moins dans le regime a haute couverture, la chimisorption de l'hydrogene intervient via la formation de liaisons de surface entre l'hydrogene atomique et les atomes d'As et Ga

High-resolution photoemission study of the interaction of hydrogen with GaAs(110) surfaces.

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