Showing papers on "Photoemission spectroscopy published in 1989"
TL;DR: In this paper, a vibrational analysis of the singlet and lower triplet state bands of vinylidene was performed in the ultraviolet (351.1-364.0 nm) photoelectron spectra of X 1A1, a 3B2, and b 3A2 states.
Abstract: The X 1A1, a 3B2, and b 3A2 states of vinylidene are observed in the ultraviolet (351.1–364.0 nm) photoelectron spectra of X 2B2 H2CC−, X 2B2 D2CC−, and X 2A’ HDCC−. The X 1A1 state exhibits vibrational structure well above the barrier for isomerization to acetylene. A strict lower bound to the lifetime of the singlet state against rearrangement is τ>0.027 ps, with an estimate of τ≊0.04–0.2 ps based on a simulation of the line shapes including rotational broadening. A vibrational analysis of the singlet and lower triplet state bands provides vibrational frequencies and estimates of the changes of molecular geometries between the anion and the neutral species. A qualitative potential energy surface for the CH2 rock mode, which closely corresponds to the reaction coordinate for isomerization, is extracted from the experimental data. The adiabatic electron affinity is EA(X 1A1 H2CC)=0.490±0.006 eV and the triplet term energies are T0(a 3B2 H2CC)=2.065±0.006 eV and T0(b 3A2 H2CC)=2.754±0.020 eV. Exp...
343 citations
TL;DR: In this paper, negative ion photoelectron spectroscopy was used to examine the O 2 − and NO − spectra of O 2 and showed the following electron affinities: EA (O 2 )=0.451±0.007 eV and EA(NO)=0.026± 0.005 eV.
246 citations
TL;DR: The surface chemistry and band bending of ammonium sulfide-treated GaAs surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy.
Abstract: The surface chemistry and band bending of the ammonium sulfide‐treated GaAs (100) surface has been studied using surface‐sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n‐type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.
107 citations
TL;DR: Data from a comprehensive study of the chemisorption of oxygen on differently prepared Si(111) surfaces indicate that the observed satellite structures in the submonolayer regime are due to excitations rather than to chemically shifted peaks from atoms in different bonding situations.
Abstract: We present new experimental results from a comprehensive study of the chemisorption of oxygen on differently prepared Si(111) surfaces, using low-energy electron diffraction and high-resolution electron spectroscopies such as x-ray photoemission spectroscopy, x-ray-initiated Auger-electron spectroscopy, and polarization-dependent ultraviolet photoemission spectroscopy. In the monolayer regime two different states of oxygen have been observed: a molecular precursor and a stable dissociated configuration. The latter is the subject of this paper. Its electronic structure and local symmetry are compatible only with a bridge-bonded atom between Si atoms in the first and second layer, respectively, with relatively little influence on the dangling bonds. The presence of a second dissociated oxygen adsorbate, e.g., a diatomiclike monoxide, is excluded by our data. The coverage dependent O 1s and Si 2p data indicate that the observed satellite structures in the submonolayer regime are due to excitations rather than to chemically shifted peaks from atoms in different bonding situations.
98 citations
TL;DR: The electronic structure of high Tc Bi2Sr2CaCu2O8 single crystals in the vicinity of the Fermi level EF was determined down to about 0.7Tc by high-resolution angle-resolved photoemission spectroscopy applying HeI and synchrotron radiation as discussed by the authors.
Abstract: The electronic structure of high-Tc Bi2Sr2CaCu2O8 single crystals in the vicinity of the Fermi level EF is determined down to about 0.7Tc by high-resolution angle-resolved photoemission spectroscopy applying HeI and synchrotron radiation. Spectra taken with 18 eV photon energy at an emission angle of 9° reveal a clear Fermi edge T > Tc. For T < Tc the emission intensity changes distinctly—at EF it decreases whereas it increases at about 100 meV below EF—accompanied by a clear shift of the emission onset to higher binding energy. These observations can be consistently explained by the opening of an energy gap of about 30 meV in the superconducting quasi-particle density of states, yielding a ratio Δ (0)/kB Tc about twice as large as the BCS value indicating that Bi2Sr2CaCu2O8 is a strong-coupling superconductor.
72 citations
TL;DR: In this paper, the X-ray photoelectron spectra of Co(NO3)2·2L with L = tdpo, tppo and tpyrp, were recorded and interpreted.
68 citations
TL;DR: In this paper, the surface of polytetrafluoroethylene (PTFE) and polyethyleneterepthalate (PET) was investigated under different gaseous atmospheres.
Abstract: We have investigated by x‐ray photoelectron spectroscopy (XPS) the surface of two polymers [polytetrafluoroethylene and polyethyleneterepthalate (PTFE) and (PET)] which were previously submitted to pulsed UV radiation delivered from an excimer laser (ArF: λ=193 nm). Treatments realized under different gaseous atmospheres allow us to point out mechanisms leading to several chemical transformations at the polymer surface. In the case of PTFE, the high‐fluence irradiations produce defluorination with surface oxidation. The latter is mainly due to air moisture. The deposition of some ablated fragments on the surface has also been observed. For PET, the major modifications are produced below the ablation threshold. They are characterized by severe deoxidation due to the loss of CO and CO2. The irradiations under oxygen and nitrogen atmospheres show the possibility of grafting new functionalities at the polymer surface.
61 citations
TL;DR: In this paper, relative partial photoionization cross sections and photoelectron branching ratios of the valence bands (6-22-eV binding energy) of bis((8)annulene)uranium(IV) are reported over the photon energy range 24-125 eV.
Abstract: Relative partial photoionization cross sections and photoelectron branching ratios of the valence bands (6-22-eV binding energy) of bis((8)annulene)uranium(IV) are reported over the photon energy range 24-125 eV. The f{sup {minus}1} band shows cross-section features attributable to 5f resonant photoemission in the vicinity of the 5d {yields} 5f giant resonant absorption (hv = 101 and 110 eV). The e{sub 2g}{sup {minus}1} and e{sub 2u}{sup {minus}1} bands also show small cross-section maxima at these energies, that for the e{sub 2u}{sup {minus}1} ionization being the more intense. The f{sup {minus}1} band shows a large maximum at 39 eV, which is assigned to a delayed maximum due to the centrifugal barrier. The three highest ionization energy bands (from ligand-based orbitals) show essentially monotonic cross section decrease with photon energy. The mapping of the intensity changes of the f{sup {minus}1} band by the e{sub 2u}{sup {minus}1} band provides strong evidence for f orbital covalency in this molecule.
60 citations
59 citations
TL;DR: In this paper, the authors examined polycrystalline Ni-Ga and Ni-In intermetallic compounds for X-ray photoemission spectroscopy and observed valence-band spectra for all the compounds are very similar to those for elemental Ni; those for Ni 3 Ga and NiIn agree rather well with the bandstructure calculations of Kubo and Wakch.
54 citations
TL;DR: It is found that the equilibrium configuration of Rh films on Ag(100) is that of a Ag-Rh-Ag sandwich, most probably flat, which is thermodynamically driven by the difference in surface free energies between Ag and Rh, and kinetically accessible because of the high mobility of the Ag atoms.
Abstract: We present the results of an investigation of Rh films on Ag(100). The films are studied using Auger-electron spectroscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, ion-scattering spectroscopy, and scanning Auger microscopy. Overlayer characteristics are examined at substrate temperatures of 300 and 600 K. We find that the equilibrium configuration is not predicted by any of the three traditional growth modes (Frank--Van der Merwe, Stranski-Krastanov, or Volmer-Weber). Rather, the equilibrium film structure is that of a Ag-Rh-Ag sandwich, most probably flat. Formation of the sandwich is thermodynamically driven by the difference in surface free energies between Ag and Rh, and is kinetically accessible because of the high mobility of the Ag atoms.
TL;DR: In this paper, the interaction of Cl2 and O2 molecules with cleaved InAs(110) surfaces was investigated at room temperature, and the changes of surface band bending and of the ionization energy as a function of exposure to the molecules mentioned were determined.
Abstract: The interaction of Cl2 and of O2 molecules with cleaved InAs(110) surfaces was investigated at room temperature. Ultraviolet photoemission spectroscopy, a Kelvin probe, and electric‐field‐induced Raman spectroscopy were used to determine both the changes of surface band bending and of the ionization energy as a function of exposure to the molecules mentioned. Chlorine as well as oxygen are inducing depletion (inversion) and accumulation layers on samples doped p‐ and n‐type, respectively. The Fermi level becomes finally pinned at 0.52 eV above the valence‐band top for both adsorbates. This behavior indicates the presence of adsorbate‐induced surface states of donor type at this energy position. With chlorine, an intermediate pinning position at 0.48 eV above the valence‐band maximum, which is below the branch point of the virtual gap states of the complex InAs band structure, is observed. This result suggests that chlorine induces surface states of acceptor character on InAs(110) surfaces as is observed w...
TL;DR: In this article, the ab initio direct configurationinteraction calculations on Na−2−5 and Na2-5 accounts for the observed patterns of photoelectron spectra and reproduce the observed excitation energies in a semiquantitative way.
Abstract: We find that the ab initio direct configuration‐interaction calculations on Na−2–5 and Na2–5 account for the observed patterns of photoelectron spectra, reproduce the observed excitation energies in a semiquantitative way and permit an assignment of cluster geometries.
TL;DR: The adsorption of ethylene on bare and cesiated Pt(111) surfaces has been investigated by means of thermal desorption spectroscopy and ultraviolet photo-emission spectrography, at temperatures ranging between 37 and 800 K.
Abstract: The adsorption of ethylene on bare and cesiated Pt(111) surfaces has been investigated by means of thermal desorption spectroscopy and ultraviolet photoemission spectroscopy, at temperatures ranging between 37 and 800 K. On the bare Pt(111) surface, a new π‐bonded C2H4 species has been observed at T 52 K, it transforms into di‐σ C2H4 and then into ethylidyne (∼300 K). Conversely, cesium preadsoption gives rise to reversibly adsorbed π‐bonded ethylene, meanwhile it inhibits the usual reaction path (di‐σ species leading to ethylidyne). Furthermore, valence‐level binding energy shifts induced by cesium adatoms have been shown to be consistent with the theoretical picture of the electrostatic potential surrounding adsorbed alkali elements.
TL;DR: The He(I) ultraviolet photoelectron spectra of benzene-fused heterocycles containing AsC and PC double bond have been recorded, and interpret MNDO and CNDO/S quantum-chemical calculation carried out to assist interpretation of the data.
TL;DR: In this paper, the authors used photoemission spectroscopy to study the band bending and chemistry of these overlayers on n-type GaAs and found that the surface Fermi level of the treated wafer is still near midgap.
Abstract: Recently, there has been a great deal of interest in Na2S⋅9H2O as a passivating chemical treatment for GaAs surfaces. It has been shown that it reduces the high surface recombination velocity characteristic of GaAs surfaces, and may offer hope for ‘‘unpinning’’ the surface Fermi level. We have used photoemission spectroscopy to study the band bending and chemistry of these overlayers on n‐type GaAs (100). Identically prepared samples show the characteristic increase in the photoluminescence signal, and have also been characterized using surface conductivity measurements. We find using photoemission that the surface Fermi level of the treated wafer is still near midgap. We also observe the chemistry at the interface, and offer a possible explanation of the photoluminescence and surface conductivity data in terms of it and the advanced unified defect model.
TL;DR: In this paper, the authors have studied near-threshold photoionisation of argon in the region of the valence satellites (32 to 49 eV) in two ways: they have measured photoelectron spectra for various constant values of photo-electron energy, from zero to 0.48 eV.
Abstract: The authors have studied near-threshold photoionisation of argon in the region of the valence satellites (32 to 49 eV) in two ways. They have measured photoelectron spectra for various constant values of photoelectron energy, from zero to 0.48 eV. Secondly, they have measured relative partial ionisation cross sections for many of the ionic states in this region, over the energy range from zero to 1.0 eV above their respective thresholds. The dominant contribution to these cross sections is observed to come from the decay of doubly excited neutral states or resonances.
TL;DR: The authors' ARUPS data show a clear Fermi edge and dispersive nature of the valence bands, suggesting the validity of the band concept for this oxide, and determined energy-band dispersion along the GAMMA-X-M-GAMMA directions in the bulk Brillouin zone.
Abstract: The electronic energy-band properties of epitaxially grown YBa/sub 2/CuO/sub 3/O/sub 7-//sub x/(001) single-crystal thin films have been investigated by angle-resolved ultraviolet photoemission spectroscopy (ARUPS) with synchrotron radiation as the light source. The (001) surfaces exhibit sharp (1 x 1) low-energy electron-diffraction patterns. Our ARUPS data show a clear Fermi edge and dispersive nature of the valence bands, suggesting the validity of the band concept for this oxide. We determined energy-band dispersion along the GAMMA-X-M-GAMMA directions in the bulk Brillouin zone. The experimental results are compared with the existing ground-state band calculations.
TL;DR: In this paper, the atomic distributions of adatoms of Y, Ba, Cu, and Ti with ordered and disordered surfaces were examined with x-ray photoemission spectroscopy and electron diffraction.
Abstract: Interface reactions of adatoms of Y, Ba, Cu, and Ti with ordered and disordered SrTiO3 (100) surfaces were examined with x‐ray photoemission spectroscopy, Auger spectroscopy, and low‐energy electron diffraction. Atomic distributions for these interfaces before and after annealing at 500 °C were determined using Ar ion sputter depth profiling. We observed strong reactions of Y and Ba with O extracted from the substrate for both ordered and disordered SrTiO3, with the strongest interactions occurring for Y on the disordered surface. These reactions were diffusion limited at 300 K, and the growth of a metal overlayer was observed with increasing coverage. Comparison of these results to those for Ti/SrTiO3 made it possible to determine the extent of the reactions and the reaction products. At elevated temperatures, more extended out‐diffusion of O from the substrate into the overlayer was observed, completing the conversion to the respective metal oxides. In contrast, Cu deposited on SrTiO3 formed clusters on...
TL;DR: In this article, the aqueous sodium sulfide surface passivation treatment, recently shown to greatly reduce the surface recombination velocity on GaAs surfaces, has been investigated with high resolution UV photoemission spectroscopy.
TL;DR: In this article, core level and valence band photoemission spectroscopy using synchrotron radiation was used to investigate the adaption of Na and Cs on the Si(100)2 × 1 surface in the monolayer range.
TL;DR: In this article, the authors studied the oxidation of a Si(100) surface cleaned using a HF solution and exposed to air, and the composition of the SiO2/Si interface.
Abstract: The oxidation of a Si(100) surface cleaned using a HF solution and exposed to air, and the composition of the SiO2/Si interface are studied in situ by high resolution (ΔE<0.3 eV) photoemission spectroscopy, using synchrotron radiation. The results are compared with those of a Si(100) surface cleaned by repeated Ar ion sputtering and annealing. The presence of SiC and SiH bonding states at the SiO2/Si interface for the HF‐cleaned Si restricts oxidation—the diffusion of oxygen atoms into the Si substrate. In the results, the proportions of Si2+ and Si3+ intermediary states at the interface increase and the interface broadens (0.85–1.0 nm), compared with the oxidation of the clean Si(100) surface.
TL;DR: In this paper, an investigation of (100) surfaces of TaC and HfC was performed using low-energy electron diffraction (LEED) and angle-resolved ultraviolet photoemission spectroscopy with synchrotron radiation.
Abstract: An investigation of (100) surfaces of TaC and HfC was performed using low‐energy electron diffraction (LEED) and angle‐resolved ultraviolet photoemission spectroscopy with synchrotron radiation. Detailed LEED I–V analyses show that, on both surfaces, carbon atoms displace outward and metal atoms inward, giving rise to (1×1) rippled relaxations, with the magnitude of the ripple being larger on TaC(100). Photoemission spectra of metal 4f levels from these surfaces show no obvious surface core‐level shifts. Using x‐ray photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES), changes in (bulk) core‐level binding energies, valence‐band structures, and local carbon environments were determined for TaCx (0.5
TL;DR: In this article, a theory of energy-, angle and spin-resolved photoemission spectroscopy of non-magnetic crystalline metals and their alloys on the basis of relativistic quantum mechanics is developed.
Abstract: The authors develop a theory of energy-, angle- and spin-resolved photoemission spectroscopy of non-magnetic crystalline metals and their alloys on the basis of relativistic quantum mechanics. In particular, the theory is applicable to cases of more than one atom per unit cell and random solid solutions. They illustrate it by explicit first-principles calculations for pure Cu, Ag and Au, ordered Cu3Au and disordered Cu0.75Au0.25.
TL;DR: In this paper, the photoelectron and Auger spectra of SiF4 have been measured, using synchrotron radiation in the 100 to 125 eV photon energy range in the vicinity of the Si2p ionization threshold.
Abstract: The photoelectron and Auger spectra of SiF4 have been measured, using synchrotron radiation in the 100 to 125 eV photon energy range in the vicinity of the Si2p ionization threshold. Partial photoionization cross sections have been obtained for outer, inner valence states and satellite states in the same energy range, together with the threshold photoelectron spectrum. At the energies of the discrete resonances observed below 112 eV, the core excited molecule is found to decay mostly by resonant Auger and to a small extent by autoionization. Among the resonant Auger pathways, those in which two electrons (rather than one) are ejected are found to play a dominant role. Above threshold, especially around the energy of the first continuum resonance, normal Auger processes are observed. Also, we offer a new interpretation of the Auger spectrum based on large configuration interaction in the final state and on the screening of the Si2p hole by the lone‐pair electrons of the fluorine atoms. We also find some evidence of cascade Auger processes which explain the formation of triply ionized molecules.
TL;DR: In this article, the vibrational state distribution of the ions generated depends on the vibronic level from which ionization occurs, and effects due to electronic configuration interaction are observed in the photoelectron spectra.
Abstract: Gas phase p‐difluorobenzene (PDFB) has been laser ionized from several vibronic levels of its 1B2u first excited electronic state. The vibrational state distribution of the ions generated depends on the vibronic level from which ionization occurs. The fundamental frequencies of five symmetric vibrations; ν2, ν3, ν4, ν5, and ν6, and three asymmetric vibrations; ν8, ν29, and ν30, of the lowest electronic state of PDFB+ have been assigned. Effects due to electronic configuration interaction are observed in the photoelectron spectra. Small peaks are also observed in the spectra which may reflect a change in geometry of the ground state cation.
15 Oct 1989
TL;DR: In this article, the HOMO orbital in C 2 H 3 X (X = F, Cl, Br and I) was reassigned with dominant iodine 5p· character rather than the π(CC) character observed for the HO orbitals of C 2 HO 3 F, C 2HO 3 Cl and C HO 3 Br, based on peak shape, vibrational profile and relative intensity change between He(I and He (II) photoelectron spectra as well as observations from the valence shell electron energy loss spectra.
Abstract: The He (I) and He (II) photoelectron spectra and the valence-shell electron energy loss spectra for C 2 H 3 X (X = F, Cl, Br and I) have been recorded. The valence-shell electron energy loss spectra were obtained at an impact energy of 3000 eV and a zero degree scattering angle. In contrast to previous studies, the HOMO orbital in C 2 H 3 I is reassigned with dominant iodine 5p· character rather than the π(CC) character observed for the HOMO orbitals of C 2 H 3 F, C 2 H 3 Cl and C 2 H 3 Br. This reordering of the assignment in C 2 H 3 I is based on considerations of peak shape, vibrational profile and relative intensity change between He(I) and He (II) photoelectron spectra as well as observations from the valence shell electron energy loss spectra. The valence shell electron energy loss spectrum of each of the monohaloethylenes is tentatively assigned as being due to transitions from the various occupied valence orbitals to common manifolds of π*(CC), σ-*(CX) and Rydberg final orbitals. A linear correlation between the CX bond strength and the term values of the 2a″→σ* (CX) transition is also demonstrated.
TL;DR: In this article, the electrochemical, spectroscopic, and structural properties of passive layers on Ni(100) grown either electrochemically in aqueous or by dosing with gaseous oxygen in ultrahigh vacuum (UHV) were compared using a UHV-electrochemical transfer system equipped for x-ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED), and high resolution electron energy loss spectrography (HREELS).
Abstract: The electrochemical, spectroscopic, and structural properties of passive layers on Ni(100) grown either electrochemically in aqueous or by dosing with gaseous oxygen in ultrahigh vacuum (UHV) were compared using a UHV‐electrochemical transfer system equipped for x‐ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy (HREELS). The two films share a similar component of several layers of anhydrous , but the electrochemical layer also contains smaller amounts of additional forms of oxygen. The elements of structural order in the two films differ in epitaxial relationships with the substrate. Similar ac impedance behaviors and dc passive current densities are seen when the clean and UHV‐oxidized Ni(100) surfaces are contacted with electrolyte at the passive potential; but 6 mC/cm2 of anodic charge must be passed to reach a steady passive state on the clean surface, while 0.8 mC/cm2 suffices on the UHV‐oxidized surface. Comparison with the very well‐defined UHV oxide allows improved precision in the characterization of the passive layer.