Valence band density of states of amorphous and trigonal selenium determined by X-ray and U.V. photoemission

The densities of states of the entire valence bands of amoprhous and trigonal selenium have been measured by X-ray (hv = 1486.6 eV) and u.v. (hv = 21.2 eV) photoemission. It is found that the primary differences in the density of states of the two forms occurs in the p-like valence bands, in particular the lower bonding set. The density of states calculated by Kramer et al. for the amorphous form is shown to be in better agreement with the experimental density of states of the trigonal form than with that of the amorphous form.     

The electronic structure of ZrSe32

The energy bands of the semiconductor ZrSe₃ have been evaluated using the KKR method. The general features of the electronic structure are expected to pertain to other transition metal trichalcogenides which have similar trigonal prismatic coordination. The calculated density of states agrees well with X-ray photoemission spectra for the valence band. The joint density of states has been evaluated and is discussed in terms of optical measurements.     

Density of states calculation for crystalline As and Sb

Valence bands of As and Sb are described by a local orbital method in which matrix elements between neighbouring atoms are calculated with no empirical paremeters. The occupied band are consistent with other calculations. The simplicity of the method allows the density of states to be obtained and this agrees closely with photoemission data. The approach should be equally valid for an amorphous network.     

Photoemission (UPS and XPS) study of crystallization of amorphous GeTe film

In situ photoemission (UPS and XPS) measurements have been performed for amorphous GeTe films. The photoemission spectra exhibit a drastic change upon thermal annealing and/or the crystallization of the film. It has been found that an amorphous GeTe film deposited onto a room temperature substrate has a 4-2 coordinated local structure, while a highly disordered amorphous GeTe film evaporated onto a cooled (77 K) substrate is largely 3-3 coordinated, and relaxes into the 4-2 coordinated structure upon thermal annealing within amorphous phase.     

Density of states modifications in amorphous and hydrogenated amorphous germanium and their effect on 3d core levels binding energy

By using photoemission and partial yield spectroscopies the conduction band edge, the valence band and the 3d core levels of amorphous germanium hydrogenated and nonhydrogenated are studied and compared to that of crystalline Ge. We measure a 0.25 eV shift of the 3d core levels of amorphous Ge as compared to crystalline Ge whereas a smaller shift and a slight line - broadening are found in hydrogenated amorphous samples with low H content. These results are discussed in term of the contribution to the self-energy due to relaxation of the valence electrons when a core hole is created.     

A comparative study of amorphous and crystalline superconducting molybdenum films by ultraviolet photoemission spectroscopy

Ultraviolet photoemission measurements at two photon energies are carried out, to understand the strong enhancement of the superconducting transition temperature T_c in the nitrogen stabilized amorphous molybdenum films. The rise of T_c can be attributed to a 40% increase of the electronic density of states at the Fermi level N(E_F) and a 15% softening of the phonon spectrum.     

Surface charging effects on valence band spectra in X-ray photoemission: Crystalline and Amorphous As2S3

In X-ray photoemission (XPS) studies on insulators, strong electric fields associated with surface charging can perturb the observed spectra. We find that the standard technique of flooding with thermal electrons to neutralize the net charge does not eliminate this effect for valence band spectra, but that the use of thin or (for photoconductors) illuminated samples does solve the problem. These conclusions are demonstrated by experiments revealing new structure in, and real differences between, the XPS valence band spectra of crystalline and amorphous As₂S₃.     

Photoemission study of the density of valence states of amorphous As2S3 and Sb2S3

The densities of valence states of amorphous As₂S₃ and Sb₂S₃ have been investigated by means of X-ray photoemission and ultraviolet photoemission spectroscopy. The spectra are interpreted on the basis of existing band structure calculations.     

Directional effects in double-beam photoemission of (1010) and (0001) Te

Strong laser beam direction vs crystal orientation dependence of double-beam photoemission spectra is reported in trigonal tellurium. This is demonstrated to be due to the large anisotropy of the electron escape probability function in such low symmetry materials, rather than specific laser polarization effects which were absent in the present experimental data.     

Electronic structure of bis(benzo)pentathienoacene in gas and solid phase: ultraviolet photoemission spectroscopy and energy band calculation

Ultraviolet photoemission spectroscopic measurements of bis (benzo)pentathienoacene were carried out in gas and solid phase. For the measurements of solid phase, vacuum deposited films in both amorphous and crystalline phase were prepared on different substrates of HOPG and polycrystalline Au, respectively. The adiabatic ionization energies were determined to be 6.8₄, 5.3₂, and 5.0₈ eV, for gas, amorphous, and crystalline phases, respectively. The spectral lineshapes were interpreted with the aid of the density functional calculations for both isolated molecule and single-crystal structure. The calculated electronic structures were further analyzed in terms of the energy band dispersion and the transport properties of charge carriers.     

Electronic states in early-late transition metal glasses: Application to Cu0.60Zr0.40

The electronic properties of amorphous Cu_0.60Zr_0.40 are studied within the two component muffin-tin EMA framework. We argue that an understanding of the photoemission spectrum of this system requires that short range order effects be incorporated in both the construction of the atomic potentials and the calculation of the average spectrum. However, we show that the essential features of the density of states can be understood on the basis of simpler calculations in which the glass is modeled as either a substitutional alloy or a liquid with just a single pair distribution function.     

III. Supraconductivité et stabilité du réseau cristalin

Although the local coordination of the constituent atoms in amorphous and crystalline As₂Te₃ is significantly different, the densities of valence states of the two structural forms as determined by high resolution monochromatized X-ray photoemission are surprisingly similar. It is shown that the nonbonding p-like features in the density of valence states of both forms depend primarily upon the chemical composition and chemical order, and not upon the coordination numbers, bond angles and structural order.     

Investigation of the band structure of germanium chalcogenides by means of photoelectron spectroscopy

The valence band photoelectron spectra of amorphous GeS, GeSe and GeTe have been measured. The ultraviolet and X-ray excited spectra show three bands associated with bonding p-states, anti-bonding and bonding s-states, respectively. In the ultraviolet photoemission spectra the p-band shows a pronounced fine structure. Features of the valence band density of states estimated on the basis of a tightbinding model are in reasonable agreement with experiment. Some problems connected with the extension of the ionicity concept of Phillips and van Vechten to the IV–VI compounds are discussed.     

Amorphous and crystalline IrSi Schottky barriers on silicon

The electro-optical properties of the films are studied by measuring the infrared optical absorption and the yield of hole photoemission across the Schottky barrier to the p-Si substrate. The Schottky barrier height of the amorphous a-IrSi to the valence band of Si is 0.17–0.18 eV. The barrier height of the polycrystalline c-IrSi depends on the degree of texturing of the silicide; the Schottky barrier height increases from 0.14 eV to 0.18 eV when the substrate temperature is increased from room temperature to 400 °C during the Ir metal deposition prior to the 500 °C silicidation. The non-linearity of the photoemission yield observed for the amorphous a-IrSi in the Fowler plot is due to an energy-dependent photon absorption of these amorphous films. An evaluation of the scattering events in the metal films shows that the mean free path for inelastic scattering is λ_in=500 nm in the amorphous a-IrSi which is one order of magnitude larger than that in the crystalline c-IrSi. The mean free path for quasi-elastic scattering λ_qe=0.3 nm, of the amorphous a-IrSi is in the order of the interatomic distance, indicating a localization of the electronic states. Received: 14 November 1997/Accepted: 12 January 1998     

First-principle study of the structural, electronic, and magnetic properties of amorphous Fe-B alloys

The structural, electronic, and magnetic properties of amorphous Fe_100−xB_x alloys (x=9, 17, 25, 27.3, 33.3, 36.3) are investigated using first-principles calculations. In these amorphous alloys, the short-range order is manifested as a series of Fe- or B-centered polyhedra such as tricapped trigonal prism, icosahedron, and bcc-like structural unit. The electron densities of states of the amorphous alloys resemble those of crystalline Fe borides, which further confirm the similarity of the local order in the amorphous and crystalline phases. All B atoms carry small negative moments of about −0.1μ_B, while small negative moments are also found on very few Fe sites for the Fe-rich compositions (x=9, 17). The average magnetic moment per Fe atom decreases nonlinearly with increasing B composition, which can be associated with the nonlinear relationship between mass density and composition.     

Elastic scattering susceptibility of the high temperature superconductor Bi2Sr2CaCu2O(8+delta): a comparison between real and momentum space photoemission spectroscopies

The joint density of states of Bi2Sr2CaCu2O(8+delta) is calculated by evaluating the autocorrelation of the single particle spectral function A(k, omega) measured from angle resolved photoemission spectroscopy (ARPES). These results are compared with Fourier transformed (FT) conductance modulations measured by scanning tunneling microscopy (STM). Good agreement between the two experimental probes is found for two different doping values examined. In addition, by comparing the FT-STM results to the autocorrelated ARPES spectra with different photon polarization, new insight on the form of the STM matrix elements is obtained. This shines new light on unsolved mysteries in the tunneling data.     

Compton profiles of trigonal and amorphous selenium

Compton profiles of trigonal and amorphous Selenium were measured with ²⁴¹Am γ-radiation using two crystalline and amorphous samples of identical geometric dimensions. As a result the difference profiles of amorphous and polycrystalline Se are reported and discussed. The valence electron Compton profile of the polycrystalline phase is compared to SCOPW-calculations by Krusius.     

Self-consistent Compton profile of selenium

The valence electron Compton profile of trigonal and polycrystalline trigonal selenium has been determined using the self-consistent OPW method. The anisotropy of the Compton profile between directions parallel and perpendicular to the c-axis is discussed. The results are compared with experimental data. The difference of the Compton profiles of the amorphous and polycrystalline phases is examined.     

CO dissociation on NiZr alloys studied by photoemission and electronic structure calculations

We present a photoemission study of the CO adsorption on amorphous NiZr alloys at various compositions. Our results indicate a distinct enhancement of dissociative adsorption even at very low Zr concentrations. These observations are supported by LCAO-type calculations of potential energy surfaces, which suggest a strong increase of backdonation into antibonding $\text{CO 2π}{}^1$ type orbitals near Zr sites.