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Resonant photoemission synchrotron radiation measurements of Fe 3 d states performed on Cd 1− x Fe x Se and Zn 1− x Fe x Se samples, with several x concentrations, are reported. Three Fe-related features have been identified: a weak one located above the top of the host material valence bands and the other two extending over the first 4 eV. The influence of the Se MVV Auger transition is analyzed. The observed features have been discussed in terms of a ligand field approach and assigned to the crystal field levels derived from the Fe 2+ ion final state configurations.

The optical properties of the semiconducting compounds (Me = Ti, V, Cr, Mn, Fe, Co, and Ni) crystallizing in the zinc-blende structure have been investigated. Reflectivity spectra of these materials have been taken at room and liquid nitrogen temperatures. The measurements have been performed in the 4 - 25 eV energy range using synchrotron radiation from the ADONE storage ring in Frascati. Comparisons between the reflectivity spectra of the ternary systems and those of the host crystal ZnSe have been made, and models explaining the influence of the transition metal ions on the electronic structure of the host crystal ZnSe have been discussed.

The absorption coefficient of several diluted magnetic semiconductors was measured below the fundamental absorption edge of the pure host compound at room temperature using the photoacoustic technique. Several absorption bands have been detected and assigned to electronic transitions between the crystal field split 3d levels of the transition metal ion. In addition, weak absorption thresholds have been observed and assigned to the ionization of the transition metal d states. An energy level diagram of the d states has been discussed.The absorption coefficient of several diluted magnetic semiconductors was measured below the fundamental absorption edge of the pure host compound at room temperature using the photoacoustic technique. Several absorption bands have been detected and assigned to electronic transitions between the crystal field split 3d levels of the transition metal ion. In addition, weak absorption thresholds have been observed and assigned to the ionization of the transition metal d states. An energy level diagram of the d states has been discussed.

The Fe related density of states of Cd 1−x Fe x Se has been investigated by means of synchrotron radiation photoemission. Energy distribution curves of the ternary compound Cd 1−x Fe x Se are presented and compared with those of the binary compound CdSe. Two Fe related structures are easily observed for all photon energies investigated (30 eV – 60 eV), whereas a third structure could be found only in the resonant photoemission region. An analysis of the costant initial state spectra suggests an atomic like interpretation of the experimental observations.

In this paper we present partial densities of states for spin-polarized antiferromagnetic phase of Zn0.5 Co0.5 Se as well as schematic layouts of the bands, obtained using the ab initio self-consistent semi-relativistic linear muffin tin orbital method. We also present, from theoretical point of view, the analysis of influence of the transition metal cobalt on the electronic structure of a pure ZnSe.

We have studied the oxidation of quaternary InGaAsP materials by NO2, using Auger electron spectroscopy for both elemental and chemical analysis of the surface. We report that NO2 induces a preferential oxidation, forming oxides of Ga, In, and P. The As remains unoxidized. From Ar+ ion milling we find that the oxide layers are fairly thin (less than 10 A), even at high exposures (greater than 1000 L) of NO2, where we obtain a saturation coverage of approximately 0.3 ML (monolayers). We have also measured electron energy loss spectra (EELS) and observe the disappearance of the surface plasmon loss feature upon oxide formation.

In this paper we present a comprehensive study of the tetrahedral semiconductor ZnSe crystallizing in the zincblende structure. The electronic structure of ZnSe has been determined first using the ab initio self-consistent linear muffin-tin orbital method with a local-density form of the exchange-correlation functional. Then it has been adjusted to reproduce the experimental energy positions of the Zn 3d bands and of the optical gap. The adjusted electronic structure, densities of states and interband optical properties are presented and compared with previous calculations. Good agreement with experimental photoemission and bremsstrahlung isochromat measurements was found after including an energy-dependent lifetime broadening. We measured the reflectivity of ZnSe with high resolution from 4 to 30 eV and the high-energy region of the spectra has been interpreted on the basis of the present calculation.

This report is an attempt to assess the validity of the binary collisions approximation by comparing TRIM and molecular dynamics in calculating the backscattering of carbon ions off a graphite surface. The TRIM calculations were performed for an amorphous target with smooth surface. In the molecular dynamics calculations, a recently available semi-empirical many body potential by Tersoff was used. The calculations were made for a perfect crystal at zero temperature, consisting of 1342 atoms in five layers. The probability of reflection was calculated as a function of energy and angle of incidence of the projectile. Compared with the binary collisions calculations, molecular dynamics predicts a significantly higher backscattering probability. For instance, at normal incidence TRIM shows less than one per cent reflection in the whole energy range up to 1 keV, whereas in molecular dynamics the reflection yield peaks around 20 eV with more than 40% reflection. The case of a head-on collision with a surface at normal incidence is discussed in detail.

A new chemoenzymatic procedure to obtain pure enantiomeric 2-arylpropionic acids is described. The one pot synthesis of (±)-2-arylpropionic acids is carried out by addition of dichlorocarbene to the O bond of arylmethylketones and hydrogenolysis of the addition product. The racemic mixture is resolved by enantiospecific hydrolysis of the racemic ethyl esters using native lipase from Candida rugosa . The good yields, the accessibility of the starting arylmethylketones and the stereospecificity of the enzymatic hydrolysis make the process interesting in order to obtain the same non steroidal antiinflammatory drugs such as Ibuprofen or Naproxen.

We report on inverse photoemission studies (IPES) obtained on freshly pealed InSe. The spectra have been taken with a Geiger-Muller-type detector and a resulting resolution of about 0.4 eV. The electron beam was not collimated thus leading to angle-integrated spectra. The data show peaks at 2.3, 5.1 and a broad feature at 7.5 eV above E F . The results are compared with previous theoretical calculations.

During 1989, following a brief all carbon phase, JET was operated with an evaporated beryllium film on all the plasma facing surfaces and then, in a third phase, with bulk beryllium used for the belt limiters and one set of antenna protection tiles. Subsequent analysis of wall components and long term samples (LTS) using Beta Backscatter and Ion Beam Analysis has been conducted to determine the condition of the First Wall and its deuterium inventory after beryllium operation. Ex-situ analysis of components where deposition occurs during operation shows mixed carbon and beryllium layers with an approximate ratio 1:1 and some localised higher Z components. The deuterium inventory situation is littled changed by the introduction of beryllium. Similar surface levels of deuterium, ~1 × 1022 atoms m−2, have been seen for both carbon and beryllium belt limiter tiles.

Collector probes were exposed to the first evaporation of beryllium in the JET vessel and to the first few plasma shots thereafter. The probes were removed under ultrahigh vacuum to an on-line analysis facility before, during and after the sequence of pulses. The amount of Be deposited during evaporation, and the amount of impurity species collected during the plasma pulses, were thus determined. Carbon was observed from the first pulse, despite the coverage of the limiters with Be, and the co-deposition with Be led to carbide formation. Oxygen was gettered very effectively by the evaporated Be layers well away from the plasma, but less efficiently where plasma deposition occurred.

Surface probes have been exposed at JET with all-carbon walls, when beryllium was evaporated onto graphite limiters, and with beryllium limiters. The aims have been to study the impurity content in the scrape-off, erosion and deposition, and the pumping of deuterium by codeposition with carbon and beryllium. Thermally activated erosion makes it difficult to study time resolved erosion close to the LCFS. In the all-carbon machine, the carbon density in the outboard scrapeoff between the belts was estimated to ~ 20% of the deuterium. With a fresh Be coating on the limiters, carbon in the SOL was initially suppressed, but increased from discharge to discharge. The D/C ratio in codeposition layers was three times larger with Be-evaporation than in all-carbon conditions. Edge profiles determined from impurity deposition became flatter during RF heating and current ramp down.

Sputtering of UF 4 by electronic excitation with fast ions has unexpectedly shown very high sputtering yields and an energy distribution of sputtered particles which decays rapidly on the high energy side. A description of the data in terms of a “thermalised ion explosion spike” has been proposed. The present discussion uses the same data to support a radically different model in which electronic relaxation generates uranium halide dimers on the surface of the UF 4 as the result of a normal energy cascade. Electronically produced sputtering of these dimers can account for the very high sputtering yields and the model accurately describes the observed energy distribution of emitted material.

A combination of angular distribution and energy spectra of sputtered atoms from amorphous UO2 material bombarded with Ar+ ions in the range 5-20 keV has given some insight into the relative importance of bulk and surface binding potentials in this material. For the energy spectra the data are well described over some 4 decades in energy by a theoretical model which includes both E B and E s terms. The surface binding term is constant at ∼1.4 eV throughout the range of argon ion energies but the effective bulk energy term EB varies from ∼3 to ∼30 eV.

Internal photoemission has been used to determine the valence‐ and conduction‐band discontinuities (ΔEv and ΔEc) in GaAs/amorphous Ge and GaP/amorphous Ge heterojunctions. The method is straightforward, accurate, and assumes a minimum of unknown parameters. We have found ΔEv =(0.43±0.05) eV and ΔEc =(0.34±0.05) eV for GaAs/a‐Ge and ΔEv =(0.88±0.05) eV and ΔEc =(0.68±0.05) eV for GaP/a‐Ge.

Heats of mixing of n-pentane, n-decane and n-tridecane with benzene were experimentally determined at 25dC. Values of the parameters associated with the quasi-lattice theory were evaluated using the experimental results together with the literature heats of mixing values for the systems benzene-n-hexane, benzene-n-heptane, benzene-n-octane, benzene-n-nonane and benzene-n-hexadecane. Using the literature model for benzene, the values of the parameters for the n-alkanes that resulted in the “best fit” of the experimental data differ from those reported in the literature. A set of parameter values is reported which permits the evaluation of heats of mixing values for binary benzene-n-alkane systems within an average absolute deviation of 3.6%, with the exception of the system benzene-n-hexadecane. On a determine experimentalement a 25dC les chaleurs de melange du pentane-n, du decane-n et du tridecane-n avec le benzene. On a etabli les valeurs des parametres relies a la theorie du “quasi-reseau”, au moyen des resultats experimentaux et des donnees publiees sur la chaleur de melange dans le cas des systemes benzene-hexane-n, benzene-heptane-n, benzene-octane-n, benzene-nonane-n, benzene-hexadecane-n. En utilisant le modele connu pour le benzene, les valeurs des parametres, en ce qui a trait aux alcanes-n, qui se sont approchees le plus des donnees experimentales different de celles qu'on a mentionnees dans la litterature. On indique une serie de valeurs de parametres qui permettent ďevaluer les chaleurs de melange des systemes binaires benzene-alcane-n, avec une moyenne ďecart absolu de 3.6%, a ľexception du systeme benzene-hexadecane-n.

Adsorption equilibria of binary benzene + cyclohexane liquid mixtures on silica gel, and heats of immersion of silica gel in pure liquids and in binary liquid mixtures of the two components were determined at 25°C. Liquid activity coefficients of benzene and cyclohexane were evaluated at 25°C and employed for calculating activity coefficients of the components in the adsorbed phase. The thermodynamic treatment of adsorption from solution proposed by Everett was adopted in this investigation. The heats of mixing in the surface phase appear to be much greater than that in the bulk liquid.