Esther Belin

Density of occupied states of intermetallic hydride NiMg2H4

Abstract Augmented plane wave band structure calculations using two possible site occupancies for hydrogen atoms were performed; energy bands, total densities of states (DOSs) and partial DOSs at the nickel, magnesium and hydrogen sites were calculated. X-ray emission spectroscopy allows an experimental determination of the distributions of occupied electronic states in solids. From this method it is possible to obtain the distribution of states around each type of atom present in an alloy or compound with a symmetry consistent with the dipole selection rules. The densities of both the Ni d and the Mg s-p states were investigated by means of (Ni 2p 3 2 ) ← (Ni 3d) and (Mg 1s) ← (Mg valence band) X-ray transitions. The experimental spectral distributions were corrected for significant oxide contribution before comparison with the calculated partial DOSs. The hydride was found to be an insulator. The nature of the Mg-H, Ni-H and H-H interactions as well as the origin of the gap are discussed and the differences between the structures proposed for the hydride are underlined.

Nickel density of states in amorphous metallic NiP

Abstract 2 p 3 2 −3 d emission and 2 p 3 2 absorption soft X-ray spectra of nickel in pure metal and in amorphous metallic NiP are presented. Differences appear in the absorption spectra which are attributed to a modification in the unoccupied density of states of nickel in amorphous NiP.

An experimental and theoretical investigation of the densities of states of dimagnesium cobalt pentahydride

Abstract Recently synthesized and characterized dimagnesium cobalt pentahydride can be considered as a member of the isoelectronic structural series of Mg 2 FeH 6 , Mg 2 CoH 5 and Mg 2 NiH 4 . In this paper we present an investigation of the electronic structure of Mg 2 CoH 5 . An experimental analysis has been made through the soft X-ray Mg Kβ and Co Lα emission spectra. From these experimental distributions, once they have been corrected for oxide contributions, information is drawn about the densities of occupied Mg 3p and Co 3d states. These results are analysed in the light of an augmented plane wave (APW) study of the energy bands, density of states (DOS) and partial wave analysis of the DOS at the atomic sites of Mg 2 CoH 5 in its cubic phase. We discuss the nature of the metal-hydrogen bonds and the character of the occupied transition metal d states. Mg 2 CoH 5 is found to be non-metallic. The origin of the energy gap is ascribed to structural features already observed in isoelectronic compounds. The investigation of empty states also appears to be important since the presence of antibonding metal-d-hydrogen-s antibonding states above the energy gap is a characteristic of this series of compounds. Thus an attempt has been made to study the unoccupied states by an analysis of Mg K absorption and by reabsorption of the Co Lα emission in the case of cobalt.

Evidence of a wide pseudo-gap in AlCuFe icosahedral alloys☆

Using X-ray spectroscopy experiments electronic distributions of both valence and conduction bands have been investigated separately in icosahedral Al63Cu25Fe12 and crystalline ω-Al7Cu2Fe. Photoemission measurements determine the position of the Fermi level; this allows comparison of the various electronic distributions. Effects of hybridization are found. Both a quite low Al density of states at the Fermi level and a rather wide pseudo-gap are observed in the icosahedral phase; such a pseudo-gap also exists in the crystalline alloy but it is smaller by a factor three. Besides hybridization effects, a possible charge transfer to Fe orbitals is proposed to interpret the empty Fe d electronic distributions of the alloys.

Occupied electronic distributions of phosphorus in electroless deposited amorphous Ni-P alloys

Abstract The electronic structure of amorphous Ni-P alloys prepared by electroless method deposition has been investigated by soft X-ray emission spectroscopy. Attention is particularly paid to phosphorus occupied electronic distributions as obtained from L 2,3 and Kβ spectra. Phosphorus-hydrogen interaction due to the presence of hydrogen produced during the sample preparation is deduced.

Empty s-d-state distributions in amorphous GexSe1−x alloys

Abstract The Ge and Se s-d conduction states in GexSe1-x glasses have been probed by studying the X-ray photoabsorption spectra at the L3 edges of Ge and Se. The experimental results show that Ge s and Se s states are totally mixed at the bottom of the conduction band; however, Ge s states seem to be predominant. As x varies, the low-energy limit of these states remain unchanged. Within the energy range of 5 eV above E F, both Ge s and Se s electronic distributions are found to be very sensitive to the local atomie arrangement; the results are discussed in relation with existing density-of-states calculations performed for amorphous GeSe with 3:3 or 4.2 coordinations.

Densities of states of black phosphorus by soft X-ray spectroscopy

Abstract We report the results of a soft X-ray investigation of the valence and conduction states of black phosphorus from which the p and s states distributions are obtained separately. The presence of pure p states is found at the upper part of the valence band. Good agreement is found with recent X-ray photoelectron spectroscopy data and with a theoretical density-of-states calculation performed for the same allotrope. The p-like densities of states of the valence band for black and red amorphous phosphorus are compared.

X-ray absorption spectroscopy study of Ge empty states in crystalline and amorphous phases, amorphous Ge:H and Si1−xGex:H

Abstract The effect of disorder, hydrogen incorporation and alloying with silicon, on the empty s, d states of germanium, has been studied by soft X-ray absorption spectroscopy. In the case of a-Ge:Hn and Si1−xGex:H alloys, the most striking point is the observation of features in the bottom of the conduction band ascribed to a genuine effect due to interaction between H 1s and Ge empty states in these materials. A slight energy shift of the mean point of the Ge L3 edge is also seen in a-Ge:H with respect to a-Ge which diminishes as H content decreases. In the hydrogenated a-Si1−xGex alloys, a slight change in the slope of the Ge L3 edge is related to fluctuations of bond lengths and angles that increase as silicon content increases.

Densities of states of semiconductors by soft X-ray spectroscopy

Abstract Soft X-ray spectroscopy (SXS) allows to obtain electronic distributions which are of a given angular momentum character due to dipole selection rules and which concern the different constituants of a solid since a core level is involved in the X-ray process. Thus from complementary emission (SXES) and photoabsorption (SXAS) spectra involving respectively the valence and the conduction bands, information on the occupied and unoccupied densities of states can be reached separately. With these two experimental methods, investigation of elemental, III–V, IV-IV or IV–VI semiconductors has been performed. We report on several results concerning p or s densities of states of Si, P and Ge in pure elements and several alloys and compounds and we compare them to theoretical calculations when available. Attention is focused on the effects of disorder, alloying and hydrogen incorporation on the densities of states.

Ru, Rh, Pd, Os, Ir, and Pt Atoms and Atomic Ions

In the following E means level energy, J internal quantum number, and g magnetic splitting factor.