Study of an α-Al2O3 single crystal by electron-induced x-ray emission spectroscopy and cathodoluminescence is reported. The relative intensities of optical emissions due to F+ and F centers have been determined as a function of the parameters of the electron beam and the annealing of the sample. It is shown that the F+ centers, i.e., the oxygen vacancies with one trapped electron, are predominant when the density of the incident electron beam increases. Similar variation is observed when the electron energy varies from 1 to 4 keV. From the comparison between x-ray and optical spectra, the F+ centers are determined to be stable defects in the bulk of the sample.

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We describe an instrument designed for studying the electronic structure of bulk, surface, and deep solid–solid interface. The analysis is made by soft-x-ray emission spectroscopy induced by electron bombardment. The target is placed under ultrahigh vacuum and can be prepared and treated in situ. High resolution is achieved both as concerns the photon energy and the electron-beam energy. Tests have been made in the dispersive mode and in the characteristic isochromat mode. In both cases experimental resolution is in good agreement with the expected one.

AhsbacL The p d a l A I and 0 valence spectral densities of a-and y-alumina in bulk and in the superficial zone of the samples are investigated using x-ray emission spectroscopy induced by electrons. These valence states are mixed over the whole width of the band. We show that changes in the atomic environment affect the hybndizalion of states io a narrow energy range. For the y-phase and superficial zones of the two phases. increased hybridization is'abserved. This is correhted with an increase in the covalent character of A I 4 bonds at the surface and the y-phase. Defect states are observed both in the gap between 0 2s and 0 2p stat= and in the optical gap; for the a-phase, a structure is seen at about 1 eV above fhe top of the valence band which we interpret as due to an oxygen-vacancy state.

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ABSTRACT:On the basis of numerical, ab initio ⌬DF and ⌬HF computations of 1s-core, 2s-core, and 2p-core ionization energies of atoms, from Li through Xe, an allometric empirical formula that was proposed for evaluating relativistic corrections (including QED effects) to nonrelativistic values is assessed for homogeneous sets of elements in the periodic table. The two coefficients involved in this formula are precisely determined for 1s-core ionization in the sets of atoms Be-Ne, Mg-Ar, Zn-Kr, and Cd-Xe; 2s-core ionization in the sets of atoms Mg-Ar, Zn-Kr, and Cd-Xe; and 2p-core ionization in the set Mg-Ar. It is shown that the medium relative error on the results obtained using this formula, with respect to those directly computed, decreases from a few percent to a few hundredths of 1% when the depth of the ionized level increases. This formula could be used to include relativistic (and QED) corrections to results yielded by simpler, nonrelativistic calculations on complex molecules involving heavy atoms.