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Showing papers on "Photoemission spectroscopy published in 1975"


Journal ArticleDOI
TL;DR: The interaction of NO with a Ni (111) surface was studied by means of LEED, AES, UPS and flash desorption spectroscopy as mentioned in this paper, and the mean adsorption energy is about 25 kcalmole.

163 citations


Journal ArticleDOI
H.P. Bonzel1, T.E. Fischer1
TL;DR: In this article, the adsorption of NO, CO and to some extent of O2 on Pt (100) and Ru (1010) surfaces was investigated by Auger electron and UV photoemission spectroscopy (UPS) at substrate temperatures below 100°C.

142 citations


Journal ArticleDOI
Neville V. Smith1, M. M. Traum1
TL;DR: In this paper, photoelectron energy spectra have been measured on the layer compounds $1T$-Ta${\mathrm{Se}}_{2}, $ 1T$ -Ta$
Abstract: Photoelectron energy spectra have been measured on the layer compounds $1T$-Ta${\mathrm{Se}}_{2}$, $1T$-Ta${\mathrm{S}}_{2}$, and $2H$-Ta${\mathrm{Se}}_{2}$ as a function of both polar and azimuthal angle of emission. Light was incident normally upon the sample and the photon energy in most of the experiments was 10.2 eV. The measurements were performed in a specially constructed ultrahigh vacuum chamber using a movable retarding potential-energy analyzer. The variations with polar angle of the positions of peaks in the spectra have been used to plot experimental energy bands which are found to compare favorably with the first-principles calculations of Mattheiss. The azimuthal dependence of the photoemission, and in particular the Ta $d$-emission intensity, was found to display strong anisotropies. X-ray orientation of the $1T$ samples revealed that if one assumes that the Ta $d$ photoelectrons originate on Ta atoms, then they propagate preferentially along directions which avoid neighboring chalcogen atoms. The relationship with atomic orbitals and band theory is discussed. In the hexagonal crystal $2H$-Ta${\mathrm{Se}}_{2}$, residual threefold rotational symmetry is observed in the Ta $d$ emission and is attributed to the shortness of the photoelectron escape depth.

120 citations


Journal ArticleDOI
TL;DR: In this paper, the application of multiple experimental techniques to silicon surface studies is discussed, including the chemisorption of oxygen on silicon at coverages up to one monolayer and the intrinsic surface states on cleaved and on annealed Si (111) surfaces.

101 citations


Journal ArticleDOI
TL;DR: In this paper, the electronic structure of the outer occupied levels of a series of hexavalent uranium (predominately uranyl) compounds was studied using x-ray photoemission spectroscopy (XPS).
Abstract: The electronic structure of the outer occupied levels of a series of hexavalent uranium (predominately uranyl) compounds was studied using x-ray photoemission spectroscopy (XPS). The changes in the spectral features of the outer occupied levels with the variation of the uranium-oxygen bond lengths (1.7-- 2.1 A) are systematically investigated. Previously unexplained spectral structure has been found to result from ligand-field splitting of the occupied U $sup 6$p$sub 3$/$sub 2$ levels. The XPS results are compared with predictions of a relativistic molecular-cluster calculation and with the results of a simple point-charge crystal-field model. When the crystalline electric fields generated by both the primary and secondary ligands are taken into consideration, excellent quantitative agreement is obtained between the XPS data and the molecular-cluster results with no parameter adjustment. (AIP)

93 citations


Journal ArticleDOI
R. T. Poole, J. Szajman1, R.C.G. Leckey1, John G. Jenkin1, John Liesegang1 
TL;DR: In this paper, the binding and separation energies of the outer electronic bands of the alkaline-earth fluorides were determined using 40.81-eV ultraviolet and Al $K\ensuremath{\alpha}$ (1486.6 eV) x-ray photoelectron spectrometry.
Abstract: Precise values have been determined for the binding and separation energies of the outer electronic bands of the alkaline-earth fluorides using 40.81-eV ultraviolet and Al $K\ensuremath{\alpha}$ (1486.6 eV) x-ray photoelectron spectrometry. Excellent agreement is found between the experimental and Born-model theoretical values for the energy separation between the outermost levels of the alkaline-earth and fluorine ions when the experimental values are corrected for relaxation (polarization) effects and when the Madelung energy alone is taken to represent the electron-lattice interaction. Very good agreement also occurs between experimental and theoretical values for the absolute binding energies. These results are accounted for by the fact that the substantial repulsive energy existing in the alkaline-earth fluorides is stored predominantly as interionic elastic potential energy and has little effect on the electronic energy levels on the ions. Comparison of the bandwidths of the alkaline-earth fluorides from the present work and alkali-metal fluorides from previous work shows that the ${\mathrm{F}}^{\ensuremath{-}}$ $2p$ valence-band width is a function of the nearest-neighbor distance and independent of the particular compound.

91 citations


Journal ArticleDOI
TL;DR: In this article, a two photon process was reported in which benzene radical cation, C6H6+, photodissociates upon irradiation from an intense argon ion laser to produce predominantly C 6H5+ and H at photon energies significantly below thermodynamic threshold.

90 citations


Journal ArticleDOI
TL;DR: In this paper, an approximate self−energy for the electron propagator was derived using the Grand Canonical averaging procedure for open shell molecules, and the connection between the overlap amplitudes and the photoionization cross section was discussed.
Abstract: An approximate self−energy for the electron propagator is derived using the Grand Canonical averaging procedure for open shell molecules. The connection between the overlap amplitudes and the photoionization cross section is discussed. A direct pole and residue search is employed to solve the Dyson equation with a second order self−energy for the oxygen molecule, yielding a theoretical photoelectron spectrum in good agreement with experimental x−ray induced spectra.

88 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that after high oxygen exposures, the epitaxial growth of NiO can be identified from the LEED pattern and the corresponding photoelectron spectrum is strongly altered and exhibits close agreement with the transition energies as calculated by Messmer et al. for a NiO 6 10- -cluster.

74 citations


Journal ArticleDOI
TL;DR: In this article, the sum rule was applied to the photoelectron bands associated with out-of-plane localized localized MO's (LO's) and a partial sum P (a) was obtained over all the out-ofthe-plane LO's and the calculated P(a) value was in good agreement with the experimental one which may be obtained by an appropriate sum of vertical ionization energies with negative signs.

74 citations


Journal ArticleDOI
TL;DR: In this article, the authors extend the range of existing absolute measurements on Ne, Kr, and Xe and report asymmetry parameters separately for processes leading to the 2P3/2,1/2 spin-orbit states of the residual ion.
Abstract: Photoelectron angular distributions for the valence p shells of the rare gases have been measured up to a photon energy of 40.8 eV (48.4 eV for Ne) using resonance radiation from a hollow-cathode discharge lamp. This work extends the range of existing absolute measurements on Ne, Kr, and Xe. Comparison with Hartree-Fock and RPAE (random-phase approximation with exchange) calculations indicates excellent agreement for Ne. However, the present results, particularly for Xe, add to earlier evidence that data for Ar, Kr, and Xe show systematic deviations from theory, especially at the higher photoelectron kinetic energies. For Kr and Xe, we report asymmetry parameters separately for processes leading to the 2P3/2,1/2 spin-orbit states of the residual ion. The Xe results indicate that β3/2 -- β1/2 is positive for λ ≥ 461 Å, but changes sign in the range λ ~ 350--400 Å. At 304 Å, β3/2 - β1/2 = -0.30, which agrees with a recent calculation based on the Dirac-Slater model. (AIP)

Journal ArticleDOI
TL;DR: In this article, X-ray photo-emission spectroscopy (XPS) was performed on thin films of Si3N4 deposited on Si using carrier injection from low-energy corona ions and a shallow junction detector.
Abstract: Transport measurements were performed on thin films of Si3N4 deposited on Si using carrier injection from low‐energy corona ions and a shallow junction detector. Large hole conduction is found for both corona polarities. Examination of the electronic structure of Si3N4 by x‐ray photoemission spectroscopy (XPS or ESCA) reveals one broad structure 10 eV wide (FWHM) at the top of the valence bands which results from the bonding of the Si 3s, Si 3p, and N 2p orbitals. This finding is consistent with the hole conduction we observe. The XPS results are compared with those from amorphous SiO2. The tops of the valence band of Si3N4 and SiO2 are found to lie 1.5±0.2 eV and 4.5±0.2 eV, respectively, below the Fermi level of a thin overlayer of gold.

Journal ArticleDOI
TL;DR: In this paper, a very narrow peak appears in the energy distribution curves (EDC) about 2.6 eV below the Fermi level Ef and grows with increasing exposure, associated with oxygen ions dissolved in the cesium metal below the surface.
Abstract: The oxidation of cesium has been studied using ultraviolet photoemission spectroscopy. Upon exposure of a fresh cesium film to oxygen, a very narrow peak appears in the energy distribution curves (EDC’s) about 2.6 eV below the Fermi level Ef and grows with increasing exposure. This peak is associated with oxygen ions dissolved in the cesium metal below the surface. After 3×10−5 Torr sec of exposure, additional structure begins to appear. This is associated with the precipitation of cesium oxides. The structure associated with the oxides changes with increasing oxygen exposure indicating the appearance of different oxides. The oxide penetrates appreciably to the surface only after strong oxide buildup has taken place beneath the surface. A sharp minimum of 0.7 eV is found in the work function over a relatively small range of oxygen exposure.


Journal ArticleDOI
TL;DR: In this article, the HeI photoelectron spectra of mono-, di-, and triacetylenes are presented and the observed energies of the radical cation states reached by electron ejection from π-orbitals can be rationalized in terms of a simple LCBO-MO model in those cases, where the molecule is planar.
Abstract: The HeI photoelectron spectra of mono-, di-, and triacetylenes are presented. In these compounds the two-centre π-orbitals of the ethynyl groups conjugate with the π-orbitals of double bonds or benzene moieties, or with the Walsh orbitals of three-membered ring systems. Assuming the validity of Koopmans' approximation, the observed energies of the radical cation states reached by electron ejection from π-orbitals can be rationalized in terms of a simple LCBO-MO model in those cases, where the molecule is planar. The corresponding numerical results for the ionization energies are in excellent agreement with experiment, if the three parameters of the model are properly calibrated. In contrast, the bands assigned to ejection from in plane π-orbitals are shifted to lower energies by ca. 0.5 eV with respect to the expectation values derived from the above model, due to ‘through-bond’ interaction with lower lying σ-orbitals. Extensive σ/π mixing occurs in the non planar compounds for all orbitals. The assignments of the spectra of diethynylmethane, 1,4-hexadiyne, 1,2-diethynylethane and of cis- and trans-diethynylcyclopropane are backed by semiempirical SCF calculations. The spectra of the cis and trans isomers of diethynylethyleneoxide and diethynylethylenesulfide are discussed by comparison with the corresponding hydrocarbons and with oxirane and thiirane respectively. Finally, the following topics are considered in detail: (a) The effect of spin orbit coupling on the spectrum of 1-iodo-1-butyne-3-ene; (b) the effect of the essentially free internal rotation in divinylacetylene on the band shapes of its photoelectron spectrum and (c) the relationship between the conjugative properties of ethylenic π-orbitals and of the Walsh-orbitals of cyclopropane.

Journal ArticleDOI
TL;DR: The first steps in the oxidation of GaAs(110) were examined through shifts in the As and Ga 3d levels as a function of oxygen exposure as discussed by the authors, showing that oxygen bonding to arsenic at the surface gives direct evidence for oxygen bonding.
Abstract: The first steps in the oxidation of GaAs(110) are examined through shifts in the As and Ga 3d levels as a function of oxygen exposure A large chemical shift is observed in the As 3d levels (about 4 eV) while the Ga 3d levels were shifted by less than 1 eV This gives direct evidence for oxygen bonding to arsenic at the GaAs(110) surface, and illustrates the change in chemical character which can take place in atoms at the surfaces of compounds (auth)

Journal ArticleDOI
TL;DR: In this paper, a time-of-flight spectrometer for photoelectron spectroscopy is described, which is based on the pulsed structure of the synchrotron radiation emitted from the storage ring (SPEAR) at SLAC with a pulse width of 1.5 nsec and a repetition period of 780 nsec.
Abstract: A time−of−flight spectrometer for photoelectron spectroscopy is described. It is based on the pulsed structure of the synchrotron radiation emitted from the storage ring (SPEAR) at SLAC with a pulse width of 1.5 nsec and a repetition period of 780 nsec. The sample is irradiated with monochromatic light from a soft x−ray grazing incidence monochromator which works in the photon energy range of 25−1500 eV. The time−of−flight spectrometer consists of a 6 in. mu−metal drift tube which can be pivoted around the sample making angularly resolved photoelectron spectroscopy feasible in both the horizontal and vertical direction. On the sample side of the drift tube a retardation sector is attached and on the other side, a fast channelplate detector. The design parameters are 100 MeV energy resolution at 5 eV at 1° angular resolution. Some preliminary results on single crystals are described.

Journal ArticleDOI
TL;DR: In this paper, the position of energy bands at symmetry points for both filled and empty bands within 1 Ry of the gap was determined using anisotropic direct transition model of photoemission applicable to cleaved singlecrystal semiconductors.
Abstract: We analyze photoemission spectra for Ge obtained for photon energies $6.5\ensuremath{\le}h\ensuremath{ u}\ensuremath{\le}25$ eV and determine the position of energy bands at symmetry points for both filled and empty bands within 1 Ry of the gap. This experimental band structure is obtained using a recently developed anisotropic direct-transition model of photoemission applicable to cleaved single-crystal semiconductors. For the band-structure determination we also employ a direct transition analysis of optical spectra obtained by others. We fit nonlocal-pseudopotential calculations to the experimentally-determined band positions, and thereby determine the importance of both energy and $l=2$, angular momentum nonlocality in the pseudopotential. Our results for the position of highlying conduction-band states suggest 0 to + 10% self-energy (exchange-correlation) corrections to the energy of electrons excited into the conduction bands. Energy bands which provide a good fit to the experimental band positions are used, along with pseudo-wave-function matrix elements, to calculate various physical properties (photoemission spectra, optical-response functions, and one-electron state densities), and the results of these calculations are compared with experiment. The quality of the fits obtained indicates that the electronic excited-state (and ground-state) properties of Ge for excitations far from the gap are described well by a one-electron model.


Journal ArticleDOI
TL;DR: In this article, the energy distribution curve of the valence of a TiC single crystal was measured by x-ray photoelectron spectroscopy (XPS) and the XPS measurement supported the augmented plane wave (APW) calculation after Ern and Switendick rather than the semi-self-consistent APW calculation after Conklin and Silversmith.
Abstract: The energy distribution curve of the valence of a TiC single crystal was measured by x-ray photoelectron spectroscopy (XPS). The XPS measurement supports the augmented plane wave (APW) calculation after Ern and Switendick rather than the semi-self-consistent APW calculation after Conklin and Silversmith. The present modified APW calculation based on the neutral-atomic-charge densities was in good agreement with the XPS measurement. Moreover, the calculation was consistent with such available experimental data as x-ray emission and absorption spectra, optical reflectivity, and low-temperature specific heat. The peak (I) arising from the C $2s$ state is isolated from the valence-band peak (II) attributed to the C $2p$, Ti $3d$, and $4s$ states. The experimental intergrated intensity ratio of peak II to peak I is 2.9 to 1.0 which is nearly equal to the theoretical value 3 to 1. The calculated density of states at the Fermi level is 0.22 electrons/(eV primitive cell), which is nearly equal to the value of 0.23 from the electronic specific heat.

Journal ArticleDOI
TL;DR: In this paper, a green-function method is used to calculate a photoelectron spectrum of C 2 N 2 including the vibrational structure, and the calculated spectrum and the experimental spectrum are in good agreement.

Journal ArticleDOI
TL;DR: In this article, the vacuum ultraviolet photoelectron spectrum of the S2(3Σ-g) molecule has been investigated and eleven ionic states of the disulphur molecule have been identified and good correlation has been found between the position of these states and those observed previously for O+2 and SO+.
Abstract: The vacuum ultraviolet photoelectron spectrum of the S2(3Σ–g) molecule has been investigated Eleven ionic states of the disulphur molecule have been identified and good correlation has been found between the position of these states and those observed previously for O+2 and SO+. Five of the observed eleven bands show well-resolved vibrational fine structure which has been analysed in order to assist with identification of the ionic state formed. The first band corresponding to the process S+2(X2IIg)â†� S2(X3Σ–g) also shows structure due to spin-orbit coupling. Relative intensities of the vibrational components within a band have been compared with calculated Franck–Condon factors in order to estimate the bond length of the ion in its various states. These bond lengths and the measured vibrational level separations have been used with the known ionization potentials of atomic sulphur to construct a potential energy diagram of S+2.


Journal ArticleDOI
TL;DR: In this paper, a LCAO-SCF calculation on the NiCO molecule is reported, in addition to the ionization potentials the vibrational structure due to ionization is calculated, and compared with those of recent semiempirical calculations on the CO-Ni system and with the photoelectron spectra of CO chemisorbed on nickel surfaces.
Abstract: A LCAO-SCF calculation on the NiCO molecule is reported. In addition to the ionization potentials the vibrational structure due to ionization is calculated. The computed ionization potentials are compared with those of recent semiempirical calculations on the CO — Ni system and with the photoelectron spectra of CO chemisorbed on nickel surfaces. We produce further evidence that the first peak in the photoelectron spectrum relates to the 5σ and 1π orbitals of CO and that the peak at higher ionization energy represents the 4σ orbital.


Journal ArticleDOI
H Hotop1, D Mahr1
TL;DR: The 584.3 AA photoelectron spectrum of Ba has been measured in a crossed-beam experiment with about 30 meV energy resolution using a 127 degrees cylindrical analyser.
Abstract: The 584.3 AA photoelectron spectrum of Ba has been measured in a crossed-beam experiment with about 30 meV energy resolution using a 127 degrees cylindrical analyser. In the single-ionization part of the spectrum, population of Ba+ ions in the states 6s, 5d, 6p, 7s, 6d, 4f, 7p, 5f, 8s, 7d, 8p and 11s is clearly detected, the double-ionization spectrum mainly consists of three lines ('natural' widths <15 meV) at 5.935(4), 5.852(4) and 5.798(4) eV together with their detected counterparts at 0.067, 0.150 and 0.204 eV. The (lowest) 5p ionization potential is deduced to be 21.014(4) eV.

Journal ArticleDOI
TL;DR: X−ray photoemission spectroscopy (XPS) is a technique that can be modified to study bulk properties, surfaces, or adsorbed species as mentioned in this paper, and it is capable of yielding bandstructure information.
Abstract: X−ray photoemission spectroscopy (XPS) is a ’’semisurface’’ technique that can be modified to study bulk properties, surfaces, or adsorbed species. As a bulk probe it is capable of yielding bandstructure information. It can distinguish amorphous from crystalline materials and is sensitive to magnetic and spatial order. Sensitivity to surface character is less pronounced. Relaxation effects are prominent in XPS spectra. Core−level binding energies of adsorbed species yield structural information if relaxation is considered. The same should be true for valence orbitals. Heterogeneous catalysis can be understood in a general sense as arising from the same origins as the relaxation energies in photoemission.

Journal ArticleDOI
TL;DR: In this article, the high resolution photoelectron spectrum of gaseous p-terphenyl and the spectral response of its photoemission in solid state were measured and both spectra were in good agreement when a slight shift was assumed.

Journal ArticleDOI
TL;DR: In this article, the ionization potentials of SF6 were studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the one-particle approximation.

Journal ArticleDOI
TL;DR: The quantitative relation between fast electron impact and photoabsorption is discussed with reference to simulation of the technique of photoelectron spectroscopy.
Abstract: The quantitative relation between fast electron impact and photoabsorption is discussed with reference to simulation of the technique of photoelectron spectroscopy. An apparatus is described that employs coincidence detection of scattered and ejected electrons resulting from ionization over a range of energy losses up to 70 eV. Absolute oscillator strengths are reported for total absorption and ionization to electronic states of water and ammonia. Relative state populations are in good agreement with photoelectron spectroscopy at 584 A. Angular distribution parameters are measured for neon, argon, and krypton. (auth)