Distribution angulaire des électrons secondaires émis par des monocristaux de cuivre sous bombardement ionique

Energy angular distributions of the secondary electronic emission from copper single crystals bombarded by 40 keV Ar⁺ ions are studied. These distributions, recorded as a function of the reception azimuth angle, with fixed polar angle, show an anisotropy which is both characteristic of the target cristalline structure and of the collected electron energy. We interpret these result in terms of bulk electron diffraction.     

Symétries de translation et de rotation des diagrammes de diffraction d'électrons lents des faces polaires {111} de GaP

The (111) faces ending with gallium and (1?1?1?) ending with phosphor in GaP crystal yield a 1 × 1 low energy diffraction pattern. This result is different from the ones previously given for the same faces of the III-V compounds exhibiting a 2 × 2 or 3 × 3 pattern. Furthermore it is not in agreement with the theories expecting a reconstruction or a faceting of the (111) faces of the blende type compounds. We think the surface equilibrium is brought about by surface electronic states. The rotation symmetry of the diffraction pattern of the (111) and (1?1?1?) faces changes with the electron energy; it is alternatively trigonal and hexagonal. This phenomena is explained thanks to a diffraction kinematical model using a limited number of atomic layers.     

Excitation par un rayonnement optique d'ondes de plasma de surface dans des structures multicouches: Coefficient de réflexion et répartition locale de l'énergie

The general dispersion relation of surface plasma oscillations (SPO) excited in a multilayered medium made of n thin films having a complex permittivity is given, using a formalism well adapted to numerical calculations. The electromagnetic (EM) energy density repartition in the films — and along the interface — as well as the reflection coefficient R of the system illuminated by a plane p-polarized wave under variable incidence are then calculated. Practical examples concerning typical metal-insulator (MI) or metal-insulator-metal (MIM) devices are then given, showing the exact localization of the excited SPO corresponding to a minimum of R and the resulting enhancement of the energy density.     

Étude par la diffraction des électrons lents et la spectroscopie auger de l'adsorption du soufre sur le platine

The adsorption of sulphur on the (111), (100) and (110) faces of platinum has been studied by LEED and Auger spectroscopy. By the combined use of radioactive S³⁵ the contents of the surface unit meshes were determined “in situ” for each state of adsorption. On the (111) face one observes a preliminary adsorption with localization of sulphur atoms at sites of maximum coordination of the metal. At higher pressures and temperatures, S-S distance contracts and a compact hexagonal arrangement, with sulphur atoms outside sites, is obtained. The thermal stability of the various structures was studied as a function of sulphur coverage. During adsorption on the (100) and (110) faces, two steps may be distinguished: the first one seems to correspond to an adsorption in sites, the second corresponds to the formation of a two-dimensional compound whose square mesh is slightly different on the two faces.     

Distributions energetiques experimentales des electrons secondaires emis par des cibles evaporees d'aluminium,de cuivre,d'or et d'argent

Secondary electron energy spectra of Al, Cu, Au and Ag evaporated layers are obtained with a two-grid retarding field spectrometer for primary beam energy between 150 eV and 2000 eV. The accuracy of the full width at half maximum and the most probable energy, and their variation with primary beam energy, are given. Comparison with recent results obtained from polycrystalline or simple-crystal massive targets suggests lower work functions for evaporated layers.     

Mesure de la temperature et des coefficients d'absorption de certaines raies de l'argon neutre dans un arc stabilise par parois et optiquement epais

Temperatures have been determined from relative line intensities in an arc stabilized in argon at atmospheric pressure. Proper corrections were made for self-absorption. Absorption coefficients have been measured for argon lines and were compared with calculated values. Good agreement was observed in regions with LTE.     

Étude par spectroscopie auger,diffraction d'électrons lents et rapides des premiers stades de la sulfuration de la face (100) de NiO par H2S

A structural study of the different stages during NiO(100) sulphurization by H₂S was carried out by RHEED, LEED and AES. On exposure to H₂S (PH₂S < 10^?5 Torr) The “clean” surface, obtained by UHV cleavage, was found to react with H₂S to produce islands of Ni(100) covered with an ordered c(2 × 2) S structure up to 300°C. Growth of Ni₃S₂ islands occurs on increasing the temperature and the exposure to H₂S.     

Distribution Radiale de la Densité des Atomes Métastables dans les Plasmas Produits par un Champ Electrique Continu ou de Haute-Fréquence

The radial density distribution of metastable Ar(³P₂) and resonant Ar(¹P₁) atoms is determined experimentally in two types of electrical discharges of cylindrical shape: the positive column plasma of a DC discharge and the plasma produced by an electromagnetic surface wave. The exitation and deexcitation rates for Ar(³P₂) by electron collisions are determined as a function of radius from the measured radial population density profile using a population density balance equation. These rate coefficients are obtained for various electron density values on the axis. The published values for these coefficients in the positive column plasma assume that they are independent of the discharge current. In this work, it is shown that these coefficients actually decrease as the electron density increases. In a more general way, the results obtained indicate that the examination of the radial density distributions of exited atoms is a powerful method for determining the kinetics of their creation and destruction.     

Étude expérimentale des électrons rétrodiffusés par les faces (001) de l'aluminium et (111) du silicium

We study the energy dependence of elastically reflected low energy electrons, as well as volume and surface plasmon excitations. The variations versus primary electron angle of incidence and surface “cleanliness” have been correlated with the electron mean free path. We show also that the collector solid angle is an important geometric factor.