Band-mapping of InP (100) along the ΓX-line

We have prepared InP (100) surfaces from wafer-material by cycles of argon ion sputtering and gentle annealing. From these samples normal-emission photoelectron spectra were recorded using photons in the energy range 10eV<h<75eV. From the results we derive the initial-state band disperison along the X-line of the 3-dimensional Brillouin zone. Our results are fully consistent with initial-state bands mapped by other authors along the KX-line. From the good agreement we conclude that the quality of the (100)-surfaces as used in our work is at least adequate for bulk band investigations.     

Angle-resolved photoemission study of NbC(100): Theory and experiment

The electronic band structure of NbC_0.83 has been investigated with angle-resolved photoelectron spectroscopy using HeI, NeI and ArI radiation. Experiments were carried out on the (100) surface with the emission azimuth lying in the (001) and the (0 1) symmetry planes. The experimental data are compared with theoretical spectra for NbC_1.0(100). The results show that most of the structures observed in the experimental spectra can be well explained by the bulk energy band structure of NbC_1.0. The large differences observed when comparing the spectra obtained in the two emission planes are discussed.     

Gap emission in ultraviolet photoemission experiments

It is shown that the gap emission observed in ultraviolet photoelectron spectra of metals takes place via a wavevector conserving excitation in the surface region localized on bulk Brillouin zone boundaries. Thus gap emission correspond to direct transitions between bulk initial statesE _i(k =k _BZ,k ) and evanescent statesE _f(k =k _BZ,k ) which are made possible by the existence of the surface. This fact can be used to map occupied bulk energy band dispersions. Examples for Silver, Copper, Gold and Platinum are given.     

Electron spectroscopy of iron disilicide

We have reported on the results of a complex investigation of iron disilicide FeSi₂ using characteristic electron energy loss spectroscopy, inelastic electron scattering cross section spectroscopy, and X-ray photoelectron spectroscopy. It has been shown that the main peak in the spectra of inelastic electron scattering for FeSi₂ is a superposition of two unresolved peaks, viz., surface and bulk plasmons. An analysis of the fine structure of the spectra of inelastic electron scattering cross section by their decomposition into Lorentzlike Tougaard peaks has made it possible to quantitatively estimate the contributions of individual energy loss processes to the resulting spectrum and determine their origin and energy.     

Electronic structure of cobalt disilicide film

The electronic structure of cobalt disilicide film has been investigated theoretically. The calculations are performed within the framework of the linearized augmented plane wave method. A combined analysis of the total and local partial densities of states and the photoelectron and x-ray emission spectra of different series for all the nonequivalent atoms of the film makes it possible to interpret the main features of the spectral characteristics of this material.     

Formation of ultrathin iron silicide layers on the single-crystal silicon surface

The solid-phase synthesis of iron silicides on the Si(100)2 × 1 surface with a 5-ML-thick iron film deposited at room temperature was studied by high-resolution photoelectron spectroscopy with the use of synchrotron radiation. Computer simulation of the measured Si 2p spectra revealed the formation of silicides in this system already under annealing at a temperature of 60°C. The process of formation consists in successive syntheses of three iron silicide phases, more specifically, monosilicide ε-FeSi, metastable disilicide γ-FeSi₂, and disilicide β-FeSi₂. The temperature ranges of existence of these phases were determined. Silicon was found to segregate on the γ-FeSi₂ surface.     

Electronic structure and spectral properties of nickel disilicide films

The film version of the linearized augmented plane-wave method is used to calculate the electronic structure, total and local partial electron densities of state, and photoelectron and x-ray emission spectra of various series for all the inequivalent atoms in a nickel disilicide film. Comparison of the results obtained with known experimental data permits interpretation of the special features of the spectral properties of this material. Fiz. Tverd. Tela (St. Petersburg) 41, 2075–2080 (November 1999)     

Excited band densities,surface resonances,and overlayer Umklapp processes observed in secondary electron emission from Ir(111) and Ir(111)(2×1)O surfaces

The Ir(111) surface shows well-defined structural features in the angle-resolved low energy secondary electron spectrum, and the angular dispersions of these features have been measured for the three principal azimuths. The spectra are interpreted principally as emission from excited bulk bands; the correlation with calculations by Noffke and Fritsche [10] is excellent. Features in the symmetric LW azimuth can be interpreted simply in terms of densities of states, but in the asymmetric pair of azimuths LU, LK there are substantial asymmetries in the secondary electron spectra although the densities of states are symmetric; it is proposed that the asymmetry is due to group velocity effects. Some additional features are interpreted as surface resonances. The Ir(111)(2×1)O surface shows additional low energy features which are interpreted as surface Umklapp of bulk state emission and as folding back of a surface resonance at the new surface zone boundary.     

On the origin of additional peaks in the photoelectron spectra of yttrium

Ultraviolet Photoemission analysis of yttrium metal reveals well defined features far below the conduction band. In order to elucidate their origin, we have used X-ray/Ultra violet photoelectron spectroscopy together with inverse photoemission. The comparison of the spectra of clean yttrium and of H exposed yttrium suggests that these structures are most probably due to hydrogen bands, hydrogen being either in a stable surface hydride form or as subsurface H.     

Correlation of conductivity and angle integrated valence band photoemission characteristics in single crystal iron perovskites for 300 K < T < 800 K: Comparison of surface and bulk sensitive methods

A single crystal monolith of La_0.9Sr_0.1FeO₃ and thin pulsed laser deposited film of La_0.8Sr_0.2Fe_0.8Ni_0.2O₃ were subject to angle integrated valence band photoemission spectroscopy in ultra high vacuum and conductivity experiments in ambient air at temperatures from 300 K to 800 K. Except for several sputtering and annealing cycles, the specimens were not prepared in situ. Peculiar changes in the temperature dependent, bulk representative conductivity profile as a result of reversible phase transitions, and irreversible chemical changes are semi-quantitatively reflected by the intensity variation in the more surface representative valence band spectra near the Fermi energy. X-ray photoelectron diffraction images reflect the symmetry as expected from bulk iron perovskites. The correlation of spectral details in the valence band photoemission spectra (VB PES) and details of the conductivity during temperature variation suggest that valuable information on electronic structure and transport properties of complex materials may be obtained without in situ preparation.     

Long-wavelength behavior of the optimal HNC/0 solution for the ground state

The set of Euler-Lagrange equations for the ground state of a symmetric film of liquid⁴He atT=0 K is solved. The optimal two-body correlation factor is determined by applying a recently proposed finite-difference relaxation method to equations formulated within the framework of the paired-phonon analysis. A relationship between the two-body correlation factor at the center of the film and that corresponding to bulk liquid is suggested. Numerical results for a rather thick film supported by an external potential are reported. A good overall agreement between results for non-uniform and uniform systems is found at the middle of the film. In particular, the long-wavelength behavior (i.e., for small momentumq parallel to the symmetry plane) of the optimal two-body correlation factor is in accord with an expression proportional toK ₀ (aq) derived from the asymptotic bulk Jastrow function. This analytic form in terms ofK ₀ leads to the correct behavior of the liquid structure functionS(q) at smallq in the limiting case of a film of infinite width.     

The XPS valence band spectra of NbC

The x-ray photoemission valence band spectra of NbC have been measured and are compared with the x-ray emission spectra and with the results from band structure calculations. This comparison leads to a large enhancement of theC2 _p photoabsorption cross section (at=1,487 eV) compared to the value calculated for the free atom. The effect of the nonmetal vacancy in the valence band can be described very well with vacancy cluster calculations.     

Structure of Electron Transitions of Corundum

The integral spectra of the dielectric permeability of corundum within the region 8–40 eV in the polarizations E C and E C are decomposed into 18 Lorentz elementary oscillators. Their principal parameters, namely, the energy E _i , halfwidth H _i , band area S _i , and height of the maximum _2max, are calculated and the main features are established. An analysis of the wellknown results obtained by two models of the reproduction of the ₂ spectra with the aid of a large number of fitting parameters and theoretical calculations of the corundum bands is carried out.     

A direct observation of the two-dimensional π-d bands for adsorbed CO

Angle-resolved photoelectron spectroscopy has been utilized to measure the dispersion and symmetry of the spectral features in thed band region of Ni induced by the adsorption of CO. Very strong alteration of thed-band emission characteristics are observed when CO is adsorbed onto Ni(110) in the (2×1) p2mg ordered phase. The high density and unique symmetry of this overlayer allows an unambigeous identification of these spectral features as the two-dimensional-d surface bands induced by the chemical bond of CO to Ni, i.e. the CO 2-Ni 3d interaction. These results make it possible to reconcile other measurements and to generate a more definitive picture of how the Blyholder model for CO-metal interaction should be applied to surfaces.     

Optical Properties of Hexagonal Zink Sulfide in a Wide Energy Range of Fundamental Absorption

Four variants of full complexes of fundamental optical functions of hexagonal zinc sulfide are determined for E c and E c polarizations. The calculations are made on the basis of experimental reflectance and theoretical permittivity spectra using the Kramers–Kronig relations. The integral permittivity spectra are resolved into elementary components. The major parameters of each component (energy maxima, half-widths, areas, and oscillator forces of the transition bands) are determined. The key features of the spectra and transition component parameters are established. The data are interpreted on the basis of the well-known band calculations.     

Electronic structure of amorphous Nb1-x Si x films studied by X-ray emission and X-ray photoelectron spectroscopy

We present valence band spectra of the amorphous system Nb_1–x Si _x (0.2x0.8), of bcc-Nb and of a-Si obtained by X-ray photoelectron spectroscopy (XPS, Al K) and X-ray emission spectroscopy (XES, Si K-emission bands). The samples were prepared as thin films by sputtering. The origin of all prominent spectral features was identified and consistently correlated to Si 3s-, Si 3p-and Nb 4d-derived states. The Nb4d-Si3p coupling is stable in binding energy over a wide concentration range. There is strong experimental evidence that the short range order changes considerably within the concentration interval 0.4x0.7, whereas the partial density of states of the Si 3p-electrons is clearly altered in the small concentration range 0.50x0.57.     

Influence of valence band states on the core hole screening in lanthanide perovskite compounds

Investigation on core level and valence band photoelectron spectra of lanthanide perovskite samples (Ag _x La_1–x CoO₃;x<0,3) and reinvestigations of metallic lanthanum and La-oxide layers are reported. Differences in preparation method during perovskite formation are leading to different quality of sample purity and different electronic properties. This could be followed by changes in the density of states near the Fermi energy. On the other hand the screening mechanism after ionization of a La 3d core hole is affected by the relative energy position of occupied valence band states with respect to the empty La 4f ^* level in the core ionized state. Changes in La 3d line profile are discussed as changes in multi electron processes (e.g. shake up or energy gain) during photoionization. We attribute the two electron process during photoemission of La 3d electrons to the well screened energy gain transition in LaCoO₃, whereas the two electron process results in a shake up transition in La₂O₃ and La(OH)₃.     

Theoretical study on the photoelectric emission spectra of a field-assisted Au-BaO thin film

The dependence of the spectral distribution of photoelectron emission from gold nano-particles embedded in BaO semiconductor thin film on applied voltage and surface plasmon resonance of gold nano-particles is predicted and investigated theoretically. The photoelectron emission response curves to light wavelength between 0.2 and are given. The dependence of the wavelength threshold on the size of gold nano-particles and external field strength is also shown. The reason that the theoretical photoelectron emission spectra is in the visible region is explained. The probabilities increased for photoexcited electrons to overcome the barrier and escape from the surface are discussed. This could be of importance in designing field-assisted thin film and finding their optimum operation conditions.     

Pulsed laser deposition of amorphous carbon nitride thin films and their electrical properties

Amorphous carbon nitride thin films were deposited by pulsed laser deposition combined with a nitrogen rf radical beam source. A structural characterization of the deposited films was performed using X-ray photoelectron and Raman-scattering spectroscopy. The Raman spectra showed that the dominant hybridization state of carbon atoms in the deposited film is sp². N 1s electron spectra were deconvoluted into three components, N bonded to pyridine-like N and/or N-sp³C (N1), substitutional N in graphite (N2), and N-O and/or N-N (N3). The proportion of N1 increased with increasing N/C atomic ratio in the film. The electrical conductivity at room temperature decreased and the Tauc optical band gap increased with increasing N/C atomic ratio. The temperature dependence of the electrical conductivity indicated that electronic conduction occurred by variable range hopping between electron localized states. The decrease in electrical conductivity with increasing N/C atomic ratio was caused by a strong electron localization due to the increased proportion of N1. PACS 81.05.Uw; 81-15.Fg; 73.61.Jc     

Systematics in the core level spectra of Th-intermetallics

We have studied the Th 4f core level spectra in a number of related Th-intemetallics, which exhibit interesting trends in terms of the intensity and the energy separation of the satellite with respect to the main signal. With the help of model calculations, we correlate the changes in the core level spectra to the density of states (DOS) in the valence band region. We have studied in detail the effect of changes in the strenght of 5f-conduction band hybridization (), the energy position of the empty 5f level ( _f ) and the DOS in the vicinity ofE _F on the spectral shape of Th 4f region. These parameters are also found to affect the binding energies of the main peaks.