E Belin

Electronic distributions of states in crystalline and quasicrystalline Al-Cu-Fe and Al-Cu-Fe-Cr alloys

Valence and conduction state distributions in a series of Al-Cu-Fe and Al-Cu-Fe-Cr alloys of different structural states and nominal compositions have been investigated by means of soft X-ray emission and photoabsorption spectroscopies. A complete description of the valence band is obtained. The DOS at EF is observed to be very low which is consistent with the high resistivity values found for the icosahedral quasicrystalline phase. The existence of a wide pseudo-gap at EF is evidenced, which is higher in the quasicrystal than in be related crystalline counterparts.

Electronic distributions of Al-Mn and Al-Mn-Si alloys

Electronic distributions of various symmetries have been investigated for both valence and conduction bands in a series of Al-Mn and Al-Mn-Si alloys of different structural states (amorphous, quasi-crystalline or crystalline) and Mn concentrations ranging from 14 to 22 at.%. Experiments have been carried out by means of soft-X-ray emission and photoabsorption spectroscopies. This allowed the authors to provide a complete description of the valence band states and to confirm the progressive opening of a small gap in the Al-sp DOS at the Fermi level with increasing Mn concentration in the alloys. At a given Mn concentration the gap is wider for the quasi-crystalline phase than for its crystalline counterpart.

Theoretical and experimental electronic distributions in AL6Mn

The authors report on a comparison between densities of states of crystalline Al6Mn calculated using the LMTO band structure method and electronic distributions obtained by means of soft X-ray spectroscopy experiments. The agreement is found to be rather good. They propose that changes in Al sites are responsible for the modifications of the densities of states observed in quasicrystalline Al-Mn alloys.

Electronic distributions in quasicrystalline Al-Pd-Mn alloys

We report on experimental valence and conduction electronic distributions of quasicrystalline Al-Mn-Pd alloys probed using the soft x-ray emission and absorption spectroscopy techniques. The various partial distributions are adjusted in the binding energy scale in order to investigate the electronic interactions characteristic in the material. In the valence band, interaction exists between Al states and Mn 3d states near the Fermi level and with Pd 4d states in the middle of the band. At the Fermi level the intensity of the Al 3p states is very low and a rather wide pseudo-gap is observed. In the conduction band, interaction exists also between Al p-Mn d states in the energy range of the absorption edge. Pd d-s states are found about 2 eV beyond the Fermi level. It is suggested that unlike the case of Mn, a small charge transfer may exist from Al to Pd states. Adjustment of Al 3p and Al p distributions at the same intensity at the Fermi level shows that the density of available Al p conduction states is dramatically decreased in the quasicrystal in comparison to pure Al. We propose that this could be connected to the existence of numerous narrow gaps and spikes in the densities of states as predicted theoretically elsewhere for crystal approximant phases with very large unit cells.

Photoelectron spectroscopy study of amorphous GaAs and Ge

Abstract The results of a detailed study of the effects of disorder and defects on the core level and valence band distributions in amorphous GaAs by X-ray photoelectron spectroscopy, are discussed and compared to those of similar experiments on amorphous Ge. We analyse the differences between the compound and the element in terms of medium-rangedisorder and we study the annealing effects. In the GaAs case, we show evidence for states associated with AsAs wrong bonds, in agreement with theoretical predictions.

XPS studies of disorder effects in flash-evaporated amorphous GaAs

Abstract XPS measurements are used to compare the As and Ga core level spectra and the valence band spectrum of flash-evaporated stoichiometric amorphous GaAs to those of crystalline GaAs. The core level data suggest that the amorphous compound is essentially chemically ordered. The most prominent modifications of the valence band due to disorder are a broadening of the upper p-bonding peak, with a parallel shift upwards of the upper edge of the band, and a filling up of the valley between this peak and the intermediate one. The ionicity gap is maintained and the s-like lower peak is little affected.

Defect states in amorphous InP

Abstract The electronic density of states of flash-evaporated amorphous In 1−x P x films, with x > 0.5, is investigated in detail by X-ray photoelectron spectroscopy and by combined optical and photothermal deflection measurements. The results are analyzed in terms of structural and chemical defects, in relation with the predictions of recent theoretical work.

Electronic structure, magnetic properties and electron transport in Al82.6−xMn17.4Six (4⩽ x ⩽ 16) quasicrystals and approximant crystals

Abstract The magnetic and electronic properties, electron transport properties and the valence band structures were studied in both the icosahedral (I) quasicrystalline phase and the corresponding (1/1 1/1 1/1) approximant phase in a series of Al 82.6− x Mn 17.4 Si x ( x =4, 6, 8, 10.1, 12, 14 and 16) alloys. The magnetic susceptibility obeys the Curie-Weiss-type temperature dependence down to 4 K in both phases, but its value in the 1/1-phase is one order of magnitude smaller than that in the I-phase. The linearly temperature dependent specific heat coefficient λ is distributed in the range 0.1-1 mJ mol −1 K −2 for the 1/1-phase, and in the range 5–7 mJ mol −1 K −2 for the I-phase. Al Ks soft X-ray emission band spectra clearly proved the presence of the pseudogap in both phases. Moreover, the Al 3p states at the Fermi level are less populated in the 1/1-phase than in the I-phase and the pseudogap in the former is wider than the pseudogap in the latter. The large difference observed in the resistivity at 300 K can be attributed to the unique difference in the valence band structure, particularly the Al 3p states, near the Fermi level between the two relevant phases.

Pseudo-gaps in crystalline and quasicrystalline alloys

Abstract We report on the distributions of valence and conduction states in various crystalline and quasicrystalline alloys. We pay special attention to the distribution of states in the vicinity of the Fermi level. We suggest that the high resistivities observed in particular for quasicrystalline AlCuFe and AlPdMn alloys could be the consequence of both the very low Al 3p density of states as the Fermi level and vanishing of the Al p conduction band over a wide energy range beyond the Fermi level.

A comparison of experimental and theoretical densities of states in CoSi2

A comparison between experimental and theoretical densities of states (DOS) is performed for CoSi2. Partial DOS of CoSi2 are studied by soft X-ray spectroscopy (SXS) through Si K beta (3p to 1s) and Co L alpha (3d to 2p32/) emission bands. In addition, X-ray photoemission spectroscopy (XPS) measurements of the valence band are presented. On the theoretical side, a scalar relativistic self-consistent augmented plane wave calculation is performed from which the partial DOS are obtained. The theoretical DOS, with a Lorentzian broadening, are compared with the experimental results and found to be in good agreement.