Showing papers on "Photoemission spectroscopy published in 1990"
TL;DR: In this paper, negative ion photoelectron spectra of Cu−n, Ag−n(n=1-10), and Au−n (n= 1-5) are presented for electron binding energies up to 3.35 eV at an instrumental resolution of 6-9 meV.
Abstract: Negative ion photoelectron spectra of Cu−n, Ag−n(n=1–10), and Au−n (n=1–5) are presented for electron binding energies up to 3.35 eV at an instrumental resolution of 6–9 meV. The metal cluster anions are prepared in a flowing afterglow ion source with a cold cathode dc discharge. In the spectra of Cu−2, Ag−2, and Au−2, the M2 X 1Σ+g←M−2 X 2Σ+u transitions are vibrationally resolved. We analyze these spectra to yield the adiabatic electron affinities, vibrational frequencies, bond length changes, and dissociation energies. The a 3Σ+u triplet states of Cu2 and Ag2 are also observed. Using experimental and theoretical data, we assign the major features in the Cu−3 and Ag−3 spectra to the transition from the linear ground state of the anion (M−31Σ+g) to an excited linear state of the neutral (M3 2Σ+u). The Au−3 spectrum is attributed to a two‐photon process, photodissociation followed by photodetachment of the Au− or Au−2 fragment. For larger clusters, we measure the threshold and vertical detachment energies...
518 citations
TL;DR: Etude de la variation de l'energie de photodetachement vertical en fonction de n, en vue de distinguer les agregats a electron de surface ou a electron interne solvate as mentioned in this paper.
Abstract: Etude de la variation de l'energie de photodetachement vertical en fonction de n, en vue de distinguer les agregats a electron de surface ou a electron interne solvate
473 citations
TL;DR: La bande de valence experimentale est comparee a la densite d'etats theorique a partir des surfaces parfaites and defectueuses.
Abstract: The electronic properties of tin dioxide single-crystalline (110) surfaces have been studied in correlation with their structure by low-energy electron diffraction, angle-integrated and resonant photoemission using synchrotron radiation [ultraviolet photoemission spectroscopy (UPS)]. Energy distribution curves were measured from the Sn 4d core levels and from the valence band. The experimental valence band is compared with the theoretical density of states (DOS) from perfect and defective surfaces. UPS difference curves, normalized to the Sn 4d intensity, reflect mainly the increase in the oxygen partial DOS when the sample is annealed at increasing temperatures up to 1000 K after sputtering. Their comparison with simulated theoretical difference curves favors a bridging oxygen termination for annealing temperatures above 900 K. After argon-ion bombardment, band-gap defect states that are not predicted by the calculations are found at a maximum density 1.4 eV above the valence-band maximum (VBM). Various degrees of resonant enhancement occur throughout the valence band when the photon energy crosses the Sn 4d\ensuremath{\rightarrow}5p photoabsorption threshold, and these are used to establish the tin-derived character of the gap states, for which a tin 5s origin is proposed. Partial-yield spectra allow the localization of unoccupied Sn 5p states in the conduction band starting from 8 eV above the VBM with a maximum at 10 eV. The Sn 4d\ensuremath{\rightarrow}5p absorption threshold also shows possible core exciton formation for sputtered surfaces only.
199 citations
IBM1
TL;DR: The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing-angle x-ray diffraction, scanning electron microscopy, and x−ray photoemission spectroscopy as discussed by the authors.
Abstract: The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing‐angle x‐ray diffraction, scanning electron microscopy, and x‐ray photoemission spectroscopy. Schottky‐barrier‐height measurements on n‐type Si (100) have also been performed in the temperature range of 95–295 K with the use of a current‐voltage technique. The results show that a metal‐rich compound with a composition in the Cu3Si range forms at low temperatures (473 K). The electronic properties of the compound are dominated by the hybridization between the Cu(d) and Si(p) valence states. A direct consequence of this hybridization is the peculiar oxidation behavior of the compound surface; both Cu and Si have been found to oxidize at room temperature. The oxidation of Si in the silicide is enhanced as compared with the oxidation of the elemental single‐crystalline Si surface. Upon annealing the oxidized surface, a solid state reaction takes place: Cu2O disappears and a thicker SiO2 layer grows, o...
193 citations
TL;DR: In this paper, the change in the chemical surface state of polished Si wafers during storage in air at room temperature was investigated for storage times up to half a year, using x-ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectrograph (HREELS).
Abstract: The change in the chemical surface state of polished Si wafers [p‐type, (100) oriented] during storage in air at room temperature was investigated for storage times up to half a year. Measurements were performed by x‐ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectroscopy (HREELS). Immediately after the HF treatment (1 min 5% HF, 2 min water rinse) vibrational spectroscopy (HREELS) shows a predominant coverage of the surface with hydride groups (80%–90% of a ML), which can be inferred from the presence of the stretching (2100 cm−1), scissor (900 cm−1) and bending (640 cm−1) vibrations in the spectra. A slight additional coverage with oxygen is proved by XPS and originates from Si‐OH groups (3670 cm−1) and oxygen‐related hydrocarbon groups (XPS). These Si‐OH groups result from an exchange reaction of Si‐F with water during the two‐minute water rinse. The development of an oxygen coverage during subsequent storage in air occurs extremely slowly and shows a logarithmic beha...
185 citations
TL;DR: In this paper, a threshold photodetachment spectrometer was used for probing the transition state region of a neutral bimolecular reaction via photodetoachment of a stable negative ion similar in structure to the neutral transition state.
Abstract: : We have developed a method for probing the transition state region of a neutral bimolecular reaction via photodetachment of a stable negative ion similar in structure to the neutral transition state. In several cases, we have found that the photoelectron spectrum of the hydrogen-bonded anion AHB(-) exhibits resolved vibrational structure which can be assigned to an unstable (AHB) complex located near the transition state for the hydrogen transfer reaction A + HB yields HA + B. The results described previously were obtained with a fixed-frequency negative ion photoelectron spectrometer. Here we report considerably higher resolution results for IHI(-) obtained on a recently constructed threshold photodetachment spectrometer. In this experiment, mass- selected ions are photodetached with a tunable pulsed laser, and only those photoelectrons produced with nearly zero kinetic energy are detected as a function of laser wavelength. The threshold photodetachment spectrum of IHI(-) shows considerably more structure than was observed in the lower resolution photoelectron spectrum. In particular, we observe narrow (30 cm) peaks due to long-lived states of the (IHI) complex which lie well above the I + HI(v=0) asymptote. (AW)
105 citations
TL;DR: In this paper, the valence ionization potentials of TTF and two derivatives, bis(ethylenedioxo)tetrathiafulvalene (BEDO-TTF) and bis(methylenedithio)tritylenedithion-tetrathyion-derived TTF, have been measured in the gas phase by photoelectron spectroscopy and compared with oxidation potentials from solution electrochemical measurements in a variety of solvents.
Abstract: Interest in organic metals and superconductors has prompted studies of the effects of chemical substituents on the organic electron donor tetrathiafulvalene (TTF). Electron-donating substituents on TTF should lead to reduced ionization potentials and generally greater electron transfer in organic donor/acceptor compounds. However, the relative electron donor abilities may also be influenced by their molecular environment and intermolecular interactions. In order to address these questions, the valence ionization potentials of TTF and two derivatives, bis(ethylenedioxo)tetrathiafulvalene (BEDO-TTF) and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), have been measured in the gas phase by photoelectron spectroscopy and compared with oxidation potentials from solution electrochemical measurements in a variety of solvents. The order of decreasing first ionization potentials is BEDT-TTF {approx} TTF (6.7 eV) > BEDO-TTF (6.46 eV).
104 citations
TL;DR: In this article, the Si−3 and Si−4 anions were obtained at 355 and 266 nm, respectively, and the spectra showed transitions to the ground and low-lying excited electronic states of the neutral clusters.
Abstract: Photoelectron spectra of the Si−3 and Si−4 cluster anions have been obtained at 355 and 266 nm. The spectra show transitions to the ground and low‐lying excited electronic states of the neutral clusters. Several of the electronic bands show resolved vibrational structure. The electronic state energies and vibrational frequencies are compared to recent ab initio calculations. The Si−4 spectrum is consistent with the prediction of a planar, symmetric rhombus for the ground state of Si4.
101 citations
TL;DR: In this article, a series of α-linked oligomers (αn with n being the number of rings) with 4-8 thiophene rings were used to investigate the electronic structure of oligothiophenes.
Abstract: Ultraviolet photoelectron spectroscopy (UPS) has been applied to the investigation of the electronic structure of oligothiophenes with 4–8 thiophene rings. In a series of α‐linked oligomers (αn with n being the number of rings), a systematic evolution of the π band is observed. Several peaks which correspond to the π band are observed in the region of 0.7–3 eV below the Fermi level (EF), and the bandwidth becomes broader with increasing n. The nonbonding π band is observed at 3.5 eV below EF and its energy is almost independent of the number of thiophene units. UPS spectra of α7 and α8 are fairly similar to the spectra of polythiophene, showing that these oligomers are good model compounds of the polymer. The ionization threshold energy of α7 and polythiophene was observed to be 5.3 eV. The effect of irregularity on the π‐electron system was also studied by using oligomers which contain a β linkage or a vinylene group at the middle of the molecule. The UPS spectra showed that the β linkages significantly ...
94 citations
TL;DR: In this paper, the potential energy curves for a number of electronic states of the O22+ dication have been calculated with the complete active space SCF (CASSCF) and multireference contracted CI (MRCCI) methods with a one-particle basis set of medium size ((8s, 6p, 2d)).
Abstract: The O22+ ion has been studied by means of electron-impact-induced and photon-induced Auger electron spectroscopy and oxygen ion fragment spectroscopy of O2. The oxygen ion kinetic energy spectrum was recorded by inverting the relevant potentials of an electron spectrometer for the detection of positive particles. The 4 Sigma - and 2 Sigma - O 1s initial core hole states have been studied using monochromatised X-ray photoelectron spectroscopy. Potential energy curves for a number of electronic states of the O22+ dication have been calculated with the complete active space SCF (CASSCF) and multireference contracted CI (MRCCI) methods with a one-particle basis set of medium size ((8s, 6p, 2d)). An analysis of the O2 Auger electron spectrum based on the computed potential curves of O22+ is presented. The autoionisation satellites are analysed and these lines correspond to molecular singly ionised final states. One line at 510.7 eV, however, is associated with an atomic-like transition. Two shake-up Auger satellites are identified by a comparison with a recent O 1s shake-up spectrum from O2.
85 citations
TL;DR: In this article, the laser photoionization mass and photoelectron spectra of propargyl radical and two partially deuterated isotopomers are measured in a supersonic molecular beam.
Abstract: The laser photoionization mass and photoelectron spectra of propargyl radical (l-C{sub 3}H{sub 3}) and two partially deuterated isotopomers are measured in a supersonic molecular beam. Radicals were produced by flash pyrolysis in a heated supersonic tube nozzle. The PES exhibits an intense origin band at 8.67 {plus minus} 0.02 eV, which is assigned to the adiabatic ionization potential previously seen by electron impact mass spectroscopy. A second photoelectron band at higher energy is assigned to the previously unobserved first excited state of the propargyl cation. One highly anharmonic vibrational progression in the cation is also observed.
TL;DR: Numerous vibrational lines are observed in the SiF 4 Si 2p photoelectron spectrum and the Z+1 core-equivalent model is assessed and changes in the molecular geometries and bonding properties of the molecules upon ionization are discussed.
Abstract: High-resolution photoelectron spectra (total instrumental width \ensuremath{\le}0.1 eV) of the Si 2p core levels of ${\mathrm{SiH}}_{4}$ and ${\mathrm{SiF}}_{4}$ were obtained using the Aladdin undulator source. The vibrationally resolved Si 2p photoelectron spectrum of ${\mathrm{SiH}}_{4}$ yields a Si-H stretching energy of 0.295\ifmmode\pm\else\textpm\fi{}0.002 eV for the core-hole ion and a lifetime width of \ensuremath{\sim}45 meV. Numerous vibrational lines are observed in the ${\mathrm{SiF}}_{4}$ Si 2p photoelectron spectrum. The Z+1 core-equivalent model is assessed and changes in the molecular geometries and bonding properties of the molecules upon ionization are discussed.
TL;DR: The ultraviolet photoelectron spectra (UPS) of mass-selected negative gallium arsenide cluster ions in the (2-50) atom size range was measured with a photon energy of 7.9 eV as discussed by the authors.
TL;DR: In this paper, the Schottky barrier height φB during contact formation was investigated for n-type β-SiC(100) for several metals with various physical and chemical properties, including Pd, Au, Co, Ti, Ag, Tb, and Al.
Abstract: Formation of Schottky barrier contacts to n‐type β‐SiC(100) was systematically investigated for several metals with various physical and chemical properties. The metals (Pd, Au, Co, Ti, Ag, Tb, and Al) were deposited onto oxygen terminated (∼1 monolayer) surfaces. Metal/β‐SiC interface chemistry and Schottky barrier height φB during contact formation were obtained by x‐ray photoemission spectroscopy; the corresponding electrical properties of thick contacts were characterized by capacitance‐voltage and current‐voltage methods. The metal/β‐SiC interface is unreactive at room temperature. X‐ray photoemission spectroscopy and electrical measurements demonstrate that these metal contacts exhibit a wide range of φB , 0.95–0.16 eV; within this range an individual contact φB value depends strongly on the metal work function in general accord with the Schottky–Mott limit.
TL;DR: In this article, an analytical description of partially resolved and unresolved vibrational progressions in valence photoelectron ionization bands is discussed. And the goodness of fit between the model and the data is discussed in each case.
TL;DR: In this article, the HeI (584 A) high resolution photoelectron spectra of As+2, Sb+2 and Bi+2 have been obtained with a high temperature molecular beam source.
Abstract: The HeI (584 A) high resolution photoelectron spectra of As+2, Sb+2, and Bi+2 have been obtained with a high temperature molecular beam source. A pure As2 beam was produced by evaporating Cu3As. Sb2 was generated as a mixture with the atoms and tetramers by evaporating the pure element, while Bi2 was generated as a mixture with only the atoms from the pure element. Vibrational structure was well resolved for the As+2 spectrum. Spectroscopic constants were derived and reported for the related ionic states. In addition, we have carried out relativistic complete active space self‐consistent field followed by multireference single + double configuration interaction calculations on these dimers both for the neutral ground states and the related ionic states. The agreements between the calculated and experimentally derived spectroscopic constants were fairly good, although the calculations tended to underestimate consistently the strength of the bonding in these heavy homonuclear diatomics.
TL;DR: In this paper, high-resolution electron microscopy and x-ray photo-emission spectroscopy were used to investigate the oxide layers of gas-evaporated Si particles as small as 100 A.
Abstract: Oxide layers grown on surfaces of gas‐evaporated Si particles as small as 100 A have been investigated Results of high‐resolution electron microscopy and x‐ray photoemission spectroscopy show that the native oxide layer (SiOx) is about 20 A thick and its chemical composition x is around 12 When the particles are annealed in air at 400 °C, the thickness of the oxide layers remains almost the same while the composition x increases up to 2 as the annealing time increases The evolution of the oxide takes place during the first 15 min of annealing Due to the increase in x, the infrared absorption band in the region of Si‐O‐Si stretching vibration shifts to higher frequencies and increases in intensity A comparison of experimental infrared spectra with those calculated by an effective medium theory suggests that the observed large width of the absorption band is caused by the particle aggregation
TL;DR: The photoelectron spectrum of the FH−2 anion is reported in this paper, which provides a probe of the transition state region for the F+H2 reaction.
Abstract: The photoelectron spectrum of the FH−2 anion is reported. The spectrum provides a probe of the transition state region for the F+H2 reaction. The experimental spectrum is compared to the recent simulation by Zhang and Miller which assumes the T5a potential energy surface for the F+H2 reaction. The experimental spectrum is substantially broader. While this may be due to inaccuracies in the T5a surface, the possibility of additional transitions to low‐lying excited electronic surfaces not included in the simulation must also be considered.
TL;DR: In this paper, high-resolution photoelectron spectra have been obtained for the tetrameric clusters of the group V elements: P4, As4, and Sb4.
Abstract: High resolution HeI (584 A) photoelectron spectra have been obtained for the tetrameric clusters of the group V elements: P4, As4, and Sb4. The spectra establish that the ground 2E states of tetrahedral P+4, As+4, and Sb+4 are unstable with respect to distortion in the ν2(e) vibrational coordinate. The E⊗e Jahn–Teller problem has been treated in detail, yielding simulated spectra to compare with experimental ones. Vibronic calculations, extended to second order (quadratic coupling) for P+4, account for vibrational structure which is partially resolved in its photoelectron spectrum. A Jahn–Teller stabilization energy of 0.65 eV is derived for P+4, which can be characterized in its ground vibronic state as being highly distorted, and highly fluxional. Linear‐only Jahn–Teller coupling calculations performed for As+4 and Sb+4, show good qualitative agreement with experimental spectra, yielding stabilization energies of 0.84 and 1.4 eV, respectively.
TL;DR: In this paper, extensive multireference configuration interaction (MRD-CI) calculations carried out with a contracted 6s5p2d1f Gaussian basis set indicate that B 2 + has a X 2 Σ g + (σ g 2 σ u 2 π g ) ground and a low-lying 1 2 Π u state (T e = 0.25 eV).
Abstract: Extensive multireference configuration interaction (MRD-CI) calculations carried out with a contracted 6s5p2d1f Gaussian basis set indicate that B 2 + has a X 2 Σ g + (σ g 2 σ u 2 σ g ) ground and a low-lying 1 2 Π u (σ g 2 σ u 2 π u ) state (T e =0.25 eV). The computed dissociation energies D e are 1.90 eV for X 2 Σ g + and 1.65 eV for 1 2 Π u . The adiabatic ionization potentials (IP) of B 2 from X 3 Σ g − (σ g 2 σ u 2 π u 2 ) into X 2 Σ g + (π u 2 →σ g , ∞) and into 1 2 Π u (π u →∞) are 8.99 and 9.24 eV, respectively; both results are expected to underestimate the true values by about 0.15 eV
TL;DR: In this article, the intrinsic linewidths of the first two image states were determined as 21±4 meV and 5±5 meV, respectively, in reasonable agreement with theoretical calculations.
Abstract: Bichromatic two-photon photoemission spectroscopy (Bi2PPES) leads to an increased signal-to-noise ratio compared to conventional two-photon photoemission spectroscopy and therefore allows the observation of the first four image potential states as well as a lineshape analysis with improved accuracy on Ag(100). The n=2 image state with a measured linewidth of 37 meV FWHM is the narrowest unoccupied structure measured on any solid surface so far. The intrinsic linewidths of the first two image states were determined as 21±4 meV and 5±5 meV, respectively, in reasonable agreement with theoretical calculations. Disordered adsorption of oxygen on Ag(100) leads to a linewidth broadening of the first and — to a lesser extent — of the second image potential state. A quantitative analysis of the broadening suggests that the underlying mechanism is lifetime shortening due to scattering of the image state electrons by the adsorbate atoms.
TL;DR: In this article, the effects of exposing a 300 K oxygen deficient SnO2(110)−4×1 surface to an oxygen plasma (0.1 Torr) have been examined using low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS), ultraviolet photo-emission spectrum analysis (UPS), ion scattering spectrograph (ISS), and surface conductivity measurements.
Abstract: The problems involved in preparing well‐defined metal oxide surfaces are well known. We are investigating low power rf oxygen plasma treatment as a method for producing metal oxide surfaces of controlled stoichiometry and structure. The effects of exposing a 300 K oxygen deficient SnO2(110)−4×1 surface to an oxygen plasma (0.1 Torr) have been examined using low‐energy electron diffraction (LEED), x‐ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), ion scattering spectroscopy (ISS), and surface conductivity measurements. Results from the plasma‐exposed surface have been compared to those obtained from a thermally oxidized (1 Torr O2, 700 K) SnO2(110) surface. LEED observations indicate that low energy ion bombardment processes associated with plasma exposure do not significantly damage (disorder) the surface. In addition, band gap states associated with oxygen vacancies are eliminated as shown by UPS. This is in accord with XPS data that show an increase in the surface O/S...
TL;DR: In this paper, variable energy photoelectron spectroscopy (PES) was used to elucidate the valence band electronic structure and bonding in tetrahedral d{sup 5} FeCl{sub 4}{sup {minus}}.
Abstract: Variable energy photoelectron spectroscopy (PES) is used to elucidate the valence band electronic structure and bonding in tetrahedral d{sup 5} FeCl{sub 4}{sup {minus}}. PES spectra obtained over the photon energy range 25-150 eV show intensity changes in the valence band features which indicate that more metal character is present in the deepest bonding levels. This is inverted from the normal electronic structure description of transition-metal complexes. The lack of off-resonance intensity in the deep binding energy satellite, which corresponds to a two-electron transition involving metal ionization plus ligand-to-metal charge transfer, indicates that little relaxation occurs on ionization. This result is confirmed by analysis of the satellite structure in the core level XPS Fe 2p spectra. PES spectra taken at the Fe 3p absorption edge, which provide insight into the bonding description of the ionized final state, show dramatic resonance intensity enhancement of the main band peaks as well as the satellite.
TL;DR: In this paper, X-ray photoemission spectroscopy was used to analyze the oxide grown at low temperature on AuxSi1−x films and found that the oxide is stoichiometric SiO2, but is structurally distinct from oxides grown on Si at high temperatures (950 °C).
Abstract: X‐ray photoemission spectroscopy was used to analyze the oxide grown at low temperature on AuxSi1−x films. It was found that the oxide is stoichiometric SiO2, but is structurally distinct from oxides grown on Si at high temperatures (950 °C). Also, unoxidized Au‐Si atom inclusions were observed in the oxide. The composition of the inclusions is dependent on the initial bulk AuxSi1−x composition.
TL;DR: The influence of the resonant intermediate states is seen in the total ionization rate as well as the photoelectron spectrum, and nonlinear ac Stark shifts are found at higher intensities.
Abstract: We have developed a new method and the necessary numerical procedures to solve the time-dependent Schroedinger equation for an atom in intense laser fields. This method allows us to obtain not only the total ionization rate, but also the emitted photoelectron spectrum. We report nonperturbative calculations at high intensity with extensions of the method to systems including a realistic pulse shape. The influence of the resonant intermediate states is seen in the total ionization rate as well as the photoelectron spectrum, and nonlinear ac Stark shifts are found at higher intensities.
TL;DR: Soft-x-ray photoemission spectroscopy of metals deposited on GaAs demonstrates that minor misorientations of the (100) surface produce major deviations from Schottky-like behavior via increased chemical interactions.
Abstract: Soft-x-ray photoemission spectroscopy of metals deposited on GaAs demonstrates that minor misorientations of the (100) surface produce major deviations from Schottky-like behavior via increased chemical interactions. The degree of chemical activity correlates with the density of dangling bonds at the [110], [111]A, and [111]B steps, producing deep levels with acceptor character which dramatically reduce the range of Fermi-level stabilization
TL;DR: In this article, a high-resolution photoelectron spectrometer designed for core level studies of gas phase volatile and involatile compounds using synchrotron radiation is briefly described.
TL;DR: In this article, the high-resolution He I photoelectron spectrum of C60 in the gas phase was reported and compared with the photo-electric spectrum of a thin film prepared by vapor deposition (one to three monolayers) on gold.
Abstract: The high-resolution He I photoelectron spectrum of C60 in the gas phase is reported and compared with the photoelectron spectrum of C60as a thin film prepared by vapor deposition (one to three monolayers) on gold. The spectra show low valence ionization bands that are very sharp and well-separated for a molecule of this size, consistent with the highly symmetric truncated icosahedral structure and theoretical calculations. The total band widths of the valence ionizations from the thin film samples are comparable to those from the gas phase species, showing that the electronic interactions between the molecules and with the surface do not significantly influence these measurements of the molecular electronic structure. The gas phase photoelectron spectra also show vibrational fine structure in the first and second ionization bands with spacings that are consistent with the two totally symmetric vibrational modes of C60. The first vertical ionization energy relative to the vacuum level is determined to be 7.61 ± 0.02 eV from these gas phase measurements.