Kinetics of thermal desorption using Auger electron spectroscopy application to cesium covered (110) gallium arsenide

We propose a new method for monitoring surface reactions kinetics using Auger Spectroscopy. It allows continuous observations of adsorption and desorption kinetics of an element A on the surface of a substrate B. The apparatus designed for this purpose transforms a standard Auger electron spectrometer into a detector measuring the rate of these surface reactions. We have used this technique to study the thermal desorption of cesium from (110) gallium arsenide. Several binding states are found

Step-driven molecular adsorption of Sb on Si( 111 )

International audienceAdsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption Auger spectroscopy. The spectra reveal that, in the submonolayer range, new adsorption states appear for the vicinal surface which do not exist for the nominal one. Quenched molecular-dynamics simulations, in which Si and Sb are modeled by many-body tight-binding potentials, allow us to interpret these new states as due to a molecular adsorption at the steps instead of a dissociative one on the terraces

Search for quantum size effects in ultrathin epitaxial metallic films

In order to investigate quantum size effects in ultrathin metal films, tunneling spectroscopy measurements have been performed in the epitaxial CoSi2/Si system, with a metal thickness ranging from 1000 Å down to 35 A, i.e. a few de Broglie wavelengths of electrons in CoSi 2. The resulting spectra show extremely rich sets of features, the origin of which are investigated. The peaks observed at low energy (-100 meV, +100 meV) are thickness independent and attributed to phonon emission by hot electrons. The peaks observed at higher energy (up to 600 meV) are thickness dependent but their physical origin is not yet fully ascertained. The absence of unambiguous electron quantization effects in these epitaxial films is discussed and tentatively attributed to small thickness fluctuations (of the order of a few monolayers), which tend to blur the quantization of the electronic energies

Effect of oxygen on the optical properties of small silicon pyramidal clusters

Optical absorption and light emission of oxygen-incorporated small silicon (Si30H40Oi) pyramidal clusters as a function of oxygen content were theoretically studied using the self-consistent semiempirical molecular orbital method (modified neglect of diatomic overlap—parametric method). In the absolute majority of the cluster configurations with low oxygen content structures, a wide spread of the optical transition energies ranging from 1.60 to 3.00 eV is observed, due to the competition between two opposite tendencies. According to the first one, connected with the increasing of the quantum confinement effects due to oxidation, the optical transition energies tend to increase, whereas the enhanced possibility of involvement of oxygen or oxygen-adjacent silicon atoms in the process tends to decrease the energy transitions

Step-driven molecular adsorption of Sb on Si( 111 )

International audienceAdsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption Auger spectroscopy. The spectra reveal that, in the submonolayer range, new adsorption states appear for the vicinal surface which do not exist for the nominal one. Quenched molecular-dynamics simulations, in which Si and Sb are modeled by many-body tight-binding potentials, allow us to interpret these new states as due to a molecular adsorption at the steps instead of a dissociative one on the terraces

Step-driven molecular adsorption of Sb on Si( 111 )

International audienceAdsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption Auger spectroscopy. The spectra reveal that, in the submonolayer range, new adsorption states appear for the vicinal surface which do not exist for the nominal one. Quenched molecular-dynamics simulations, in which Si and Sb are modeled by many-body tight-binding potentials, allow us to interpret these new states as due to a molecular adsorption at the steps instead of a dissociative one on the terraces

Superconductivity in ultra-thin CoSi2 epitaxial films

The first results on the superconducting properties of ultra-thin epitaxial CoSi2 films are reported. The metal films are obtained by solid phase epitaxy under ultra high-vacuum conditions, with thicknesses ranging from 600 Å down to 50 A. These films are stable against temperature cycling from 350 mK up to room temperature and superconducting for thicknesses down to 100 Å. Results showing a reduction of the transition temperature and variations of the critical magnetic field with decreasing film thicknesses are presented. Furthermore, for very low film thicknesses (i.e. 100 A), an intermediate plateau is observed in the resistivity versus temperature curve. The physical origin of these phenomena is briefly discussed.Nous présentons les premiers résultats de supraconductivité obtenus sur des films épitaxiés de CoSi2 ultra-minces. Ces films métalliques, d'épaisseur variant de 600 Å à 50 Å sont obtenus par épitaxie en phase solide sous ultra-vide. Ces films sont stables lors de cycles en température de 350 mK jusqu'à la température ambiante et supraconducteurs pour des épaisseurs supérieures à 100 Å. Nous présentons des résultats montrant une diminution de la température critique ainsi que des variations du champ magnétique critique pour des épaisseurs décroissantes des films métalliques. De plus, nous observons un plateau intermédiaire dans la courbe de résistivité en fonction de la température pour le film de plus faible épaisseur (i.e. 100 Å). L'origine physique de ces phénomènes est brièvement discutée