Showing papers on "Photoemission spectroscopy published in 1996"
TL;DR: In this paper, the valence band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x-ray photoemission spectroscopy.
Abstract: The valence‐band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x‐ray photoemission spectroscopy. A significant forward–backward asymmetry was observed in the InN/GaN–GaN/InN and InN/AlN–AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN.
639 citations
TL;DR: The chemistry and electronic properties of interfaces formed between thin films of the archetype molecular organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride and reactive and nonreactive metals are investigated via synchrotron radiation photoemission spectroscopy.
Abstract: The chemistry and electronic properties of interfaces formed between thin films of the archetype molecular organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) and reactive and nonreactive metals are investigated via synchrotron radiation photoemission spectroscopy. In, Al, Ti, and Sn react at room temperature with the anhydride group of the PTCDA molecule, producing heavily oxidized interface metal species and thick interfacial layers with a high density of states in the PTCDA band gap. The penetration of the reactive metal species in the PTCDA film is found to be inversely related to their first ionization energy. The noble metals Ag and Au form abrupt, unreacted interfaces. The chemical and structural results correlate well with the electrical properties of the interfaces that show Ohmic behavior with the reactive metal contacts and blocking characteristics with the noble metals. The Ohmic behavior of the reactive metal contacts is ascribed to carrier hopping and/or tunneling through the reaction-induced interface states. \textcopyright{} 1996 The American Physical Society.
332 citations
TL;DR: A nested interface band alignment with ΔEv=1.36±0.07 eV was obtained in this paper. But the alignment was not applied to the AlN/GaN (0001) heterojunction interface.
Abstract: X‐ray photoemission spectroscopy has been used to measure the valence band offset ΔEv for the AlN/GaN (0001) heterojunction interface. The heterojunction samples were grown by reactive molecular beam epitaxy on 6H–SiC (0001) substrates. A nested interface band alignment with ΔEv=1.36±0.07 eV is obtained (ΔEc/ΔEv=52/48).
222 citations
TL;DR: The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule.
Abstract: The 351-nanometer photoelectron spectrum of the planar cyclooctatetraene radical anion (COT·-) shows transitions to two electronic states of cyclooctatetraene (COT). These states correspond to the D4h 1A1g state, which is the transition state for COT ring inversion, and the D8h 3A2u state. The electron binding energy of the 1A1g transition state is 1.099 ± 0.010 electron volts, which is lower by 12.1 ± 0.3 kilocalories per mole than that of the 3A2u state. The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule. Vibrational structure is observed for both features and is readily assigned by use of a simple potential energy surface.
222 citations
TL;DR: In this article, the authors used negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques to study the formation of dipole-bound anions of CH 3 NO 2.
Abstract: ~Received 28 December 1995; accepted 9 May 1996! Conventional ~valence! and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe( nf ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*’1361 which is characteristic of the formation of dipole-bound anions @m~CH 3 NO 2 !53.46 D#. However, the breadth ~Dn’5, FWHM! of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ‘‘doorway’’ dipole anion state. Studies of the electric field detachment of CH 3NO2 formed through the Xe( nf ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 1263 meV. Photodetachment of CH3NO2 and CD3NO2 formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ~valence bound! anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ~v850, v950! transitions in the photoelectron spectra of CH3NO2 and CD3NO2 yields adiabatic electron affinities of 0.2660.08 and 0.2460.08 eV, respectively. © 1996 American Institute of Physics.@S0021-9606~96!02831-0#
181 citations
TL;DR: In this article, a method for global analysis of x-ray photoelectron spectra of plasma-deposited polymer films is presented, which is based on fitting a series of spectra obtained by monitoring the surface composition of a plasma polymer film over extended periods of time after deposition.
Abstract: A protocol for global analysis of x-ray photoelectron spectra of plasma-deposited polymer films is presented. These materials are difficult to analyse because of the multitude of different chemical groups present. The combination of different primary and secondary binding energy shifts results in relatively broad, featureless photoelectron peaks. The protocol is based on fitting a series of spectra obtained by monitoring the surface composition of a plasma polymer film over extended periods of time after deposition. Information obtained from this first round of curve-fitting is used in the form of additional constraints for a second round of fitting. This leads to a self-consistent procedure which is akin to a global approach to curve-fitting. To illustrate application of this method, results of a study of ann-heptylamine plasma polymer are described. The spectral changes on ageing provided clear evidence for radical-initiated oxidation reactions. These reactions generated additional radicals, which sustained the oxidation process for many months and not only led to substantial incorporation of oxygen into the material (forming a variety of carbon–oxygen functionalities) but also to conversion of most of the existing carbon–nitrogen functionalities to an oxidized form.
171 citations
TL;DR: In this paper, the electron affinity of the corresponding neutral cluster has been determined from anion photoelectron spectra of Ge−n, n=2-15, using an incident photon energy of 4.66 eV.
Abstract: Anion photoelectron spectra of Ge−n, n=2–15, have been measured using an incident photon energy of 4.66 eV. In addition, the spectra of Ge−2, Ge−3, and Ge−4 have been measured at photon energies of 3.49 and 2.98 eV. From these spectra the electron affinity of the corresponding neutral cluster has been determined. Vibrational frequencies and term values for several electronic states of Ge−2 and Ge−3 have been determined. Vibrational structure in the 3B3u excited state of Ge4 has been resolved using zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The assignment of the spectra of Ge−3 and Ge−4 is facilitated by a comparison to the similar spectra of Si−3 and Si−4, respectively. The spectra of the larger clusters, Ge−n, n=5–15, are characterized by many broad structureless features which indicate the presence of multiple electronic transitions. Several of these were assigned based on comparison with previous ab initio calculations on germanium and silicon clusters.
146 citations
TL;DR: In this paper, the authors investigated the interaction of oxygen on Pd(110) by temperature programmed desorption (TPD), ultraviolet photoemission spectroscopy (UPS) and x-ray photoelectron spectrography (XPS).
120 citations
TL;DR: Energy-resolved photoelectron spectroscopy in combination with femtosecond pump-probe and molecular beam techniques are used to map molecular dynamics along the internuclear coordinate as mentioned in this paper.
Abstract: Energy-resolved photoelectron spectroscopy in combination with femtosecond pump-probe and molecular beam techniques are used to map molecular dynamics along the internuclear coordinate The capabilities of this method are demonstrated on the one-dimensional wave-packet motion on electronically excited states of the sodium dimer: by recording transient photoelectron spectra in a pump-probe experiment we are able to follow the molecular wave-packet motion on neutral electronic states along all energetically allowed internuclear distances simultaneously \textcopyright{} 1996 The American Physical Society
116 citations
TL;DR: In this article, the angle-resolved N 1s photoelectron spectrum was measured with high resolution in the threshold region and the vibrational energy of the core ionized molecule was analyzed.
Abstract: The angle-resolved N 1s photoelectron spectrum of has been measured with high resolution in the threshold region An analysis of the vibrational fine structure yields a vibrational energy of and a lifetime broadening of for the core-ionized molecule As in the case of C 1s ionization of CO, the vibrational fine structure changes considerably with photon energy in the region of both the shape resonance and the double excitations Both the vibrationally resolved partial photoionization cross sections and asymmetry parameters have been determined in this photon energy range The calculated cross sections in the literature are in reasonable agreement with experiment In addition, we have measured the cross sections and asymmetry parameters of the most intense direct and conjugate shake-up satellites The behaviour of the satellites is found to differ significantly from that of the corresponding C 1s satellites of CO
114 citations
TL;DR: The network topology of the model is analyzed through partial pair correlations, angle distributions, partial static structure factors, and ring structures, and the localization of the electronic states is analyzed.
Abstract: We present results of an ab initio molecular-dynamics study of glassy ${\mathrm{GeSe}}_{2}$ using a 216 atom model. The network topology of our model is analyzed through partial pair correlations, angle distributions, partial static structure factors, and ring structures. The total static structure factor and first sharp diffraction peak are in good agreement with experiment. The vibrational density of states and dynamical structure factor are in good agreement with experimental results as well. We have visualized the normal modes vectors in order to qualitatively understand their motion. The electronic density of states compares very well with experimental ultraviolet photoemission spectroscopy and x-ray photoemission spectroscopy measurements. The localization of the electronic states is analyzed. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, high-resolution, synchrotron radiation excited valence photoelectron satellite spectra, taken at the magic angle, of all the rare gases, He, Ne, Ar, Kr and Xe are presented.
TL;DR: In this article, the electron affinity of diamond and AlGaN surfaces was studied by UV photoemission spectroscopy and it was shown that H terminated diamond surfaces exhibit negative electron affinity while oxide terminated surfaces exhibit a positive electron affinity.
TL;DR: In this article, the energy dependence of the electron lifetime in graphite was measured using femtosecond time-resolved photoemission spectroscopy, and the lifetime was found to be inversely proportional to the excitation energy above the Fermi level.
Abstract: The energy dependence of the electron lifetime in graphite was measured using femtosecond time-resolved photoemission spectroscopy The lifetime was found to be inversely proportional to the excitation energy above the Fermi level, ie, $({E\ensuremath{-}E}_{F}{)}^{\ensuremath{-}1}$, in sharp contrast to that of metals, whose lifetime is found to be proportional to $({E\ensuremath{-}E}_{F}{)}^{\ensuremath{-}2}$ The results are in agreement with the prediction of the layered electron gas theory, which suggests that electron-plasmon interactions dominate the lifetime of electrons in a layered electron gas, even for small excitation energies, due to interlayer plasmon coupling
DSM1
TL;DR: X-ray photoelectron spectroscopy (XPS) measurements on SiO2-ZrO2mixed oxides with varying Si/Zr ratios are presented in this article.
TL;DR: In this paper, the x-ray photoelectron spectroscopy of zinc sulphide particles after copper(II) activation at pH 9 has been studied by using X-ray spectrograms, showing that high binding energy components and satellites of the Cu 2p signals, characteristic of copper hydroxide overlayers, reduced in intensity with increased xray exposure.
Abstract: The surfaces of zinc sulphide particles after copper(II) activation at pH 9 have been studied by x-ray photoelectron spectroscopy The influence of x-ray irradiation time on the forms and intensities of the photoelectron signals from zinc sulphide particles activated at various copper coverages was investigated High binding energy components and satellites of the Cu 2p signals, characteristic of copper(II) hydroxide overlayers, reduced in intensity with increased x-ray exposure An associated reduction in the concentration of surface oxygen was also observed Differential charging analysis and curve fitting reveal the dehydration of Cu(OH) 2 to CuO, followed by photoreduction of CuO to Cu 2 O No evidence was found for x-ray irradiation enhancement of continued Cu activation of or diffusion into ZnS
TL;DR: In this article, the photodissociation dynamics of the I 2 − anion have been studied in real-time using femtosecond photoelectron spectroscopy, where the anion is excited to a dissociative electronic state with an ultrafast pump pulse, and the photo-electron spectrum is measured by photodetachment with a second, ultrafast probe pulse.
TL;DR: In this article, angle-resolved photoemission spectroscopy measurements of the excitation gap in underdoped superconducting thin films were obtained, and it was shown that the anisotropic gap persists well above the BCS mean field theory result.
Abstract: We report angle-resolved photoemission spectroscopy measurements of the excitation gap in underdoped superconducting thin films of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Dy}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. As ${T}_{c}$ is reduced by a factor of 2 by underdoping, the superconducting state gap $\ensuremath{\Delta}$ does not fall proportionally, but instead stays constant or increases slightly, in violation of the BCS mean-field theory result. The different doping dependences of $\ensuremath{\Delta}$ and $k{T}_{c}$ indicate that they represent different energy scales. The measurements also show that $\ensuremath{\Delta}$ is highly anisotropic and consistent with a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ order parameter, as in previous studies of samples with higher dopings. However, in these underdoped samples, the anisotropic gap persists well above ${T}_{c}$. The existence of a normal state gap is related to the failure of $\ensuremath{\Delta}$ to scale with ${T}_{c}$ in theoretical models that predict pairing without phase coherence above ${T}_{c}$.
TL;DR: This experiment shows that XPCS can be performed in a wide time range and opens up a new opportunity for the study of the dynamics of nontransparent media.
Abstract: We have used an intense coherent x-ray beam and a real time digital autocorrelator to study the low frequency dynamics of colloidal palladium in glycerol by x-ray photon correlation spectroscopy (XPCS). The translational diffusion was studied in the q range from 1.5 3 1023 to 6 3 1023 A21 and in the temperature range from 279 to 293 K. The measured relaxation rates were proportional to q2 and inversely proportional to viscosity as expected for a translational diffusion process. This experiment shows that XPCS can be performed in a wide time range (1024 to 100 s) and opens up a new opportunity for the study of the dynamics of nontransparent media. [S0031-9007(96)01912-6]
TL;DR: In this paper, the authors measured absolute VUV optical absorption cross sections for ozone between 325 and 110 nm (3.0 - 11.3 eV) using a synchrotron radiation source.
Abstract: Absolute VUV optical absorption cross sections for ozone have been measured between 325 and 110 nm (3.0 - 11.3 eV) using a synchrotron radiation source. Vibrational fine structure is resolved in Rydberg bands and comparison of this with the limiting bands in the photoelectron spectrum confirms that the order (increasing ionization energy) of the three lowest ionization bands is . Near-threshold electron energy-loss spectra have also been recorded. In these, in addition to the known triplet states between 1 and 2 eV, a low-lying triplet state has been located around 3.4 eV and several others between 6 and 9 eV. Characterization of the valence states (both optically allowed and forbidden) are discussed in relation to the results of early theoretical computations which seem to give a good account of the ozone spectrum.
TL;DR: The TR-PES investigation of the energy dependence of the electron relaxation lifetime in highly oriented pyrolytic graphite provides the first experimental evidence that the dominant scattering process in layered materials can be electronplasmon scattering, even for excitations close to the Fermi level.
Abstract: We comment on the theoretical interpretations applied to a recent experiment on electron lifetime in graphite. We point out that the acoustic-plasmon excitations in a layered two-dimensional electron system do not produce a linear energy dependence for the Coulomb scattering rate.
TL;DR: The electronic structures of the itinerant ferromagnets Cr 12dTe (d 5 0.05, 0.25, and 0.375! have been studied by photoemission spectroscopy.
Abstract: The electronic structures of the itinerant ferromagnets Cr 12dTe ( d 5 0.05, 0.25, and 0.375! have been studied by photoemission spectroscopy. The valence-band spectra are compared with the density of states given by band-structure calculations. In spite of the itinerant nature of the d electrons, disagreement between the photoemission spectra and the band-structure calculations exists in the magnitude of the d-band exchange splitting and the spectral weight at the Fermi level and 2‐ 4 eV below it: The occupied d band for d50.05 is shifted away from the Fermi level; the observed spectral weight at the Fermi level is significantly suppressed compared with the band-structure calculations for d50.05 and 0.375, where the nominal d-electron numbers are close to integers 4 and 3, respectively. Configuration-interaction cluster-model calculations have been made for d50.05 and 0.375 to explain the spectral weight distribution in the high-binding-energy ~2‐4 eV! region in terms of electron-correlation effects. The d-d on-site Coulomb energy is estimated to be significant, U;2 eV, and nearly equal to or smaller than the charge-transfer energy D; 2‐3 eV.
TL;DR: In this paper, the authors studied the interface formation of a vinylene phenylene oligomer with a Ca substrate using photoemission spectroscopy and proposed an energy level diagram of the oligomer-Ca interface.
Abstract: We have studied the interface formation of a vinylene phenylene oligomer with a Ca substrate using photoemission spectroscopy. The evolution of core and valence spectra during the deposition of the oligomer on Ca has indicated the molecular energy level bending. The total energy level bending was 0.5 eV and the thickness of the level bending region was about 100 A. We propose an energy level diagram of the oligomer‐Ca interface based on the information obtained from the photoemission spectra.
TL;DR: In this paper, state-selected electron spectra characterizing the transition state in the Penning ionization of N2 by He*(21S) have been measured in crossed supersonic beams at seven collision energies in the range E = 1.5−4.2 kcal/mol.
Abstract: State-selected electron spectra characterizing the transition state in the Penning ionization of N2 by He*(21S) have been measured in crossed supersonic beams at seven collision energies in the range E = 1.5−4.2 kcal/mol. The spectral peaks are assigned by analogy with the photoelectron spectrum of N2 to the three lowest electronic states X2Σg+, A2Πu, and B2Σu+ of N2+, as in earlier work. Evidence is presented, however, based on vibrational spacings, that the X-state vibrational distribution is bimodal. The spectra are least-squares analyzed to yield nascent electronic-state branching fractions, vibrational populations, and spectral line shifts and widths, all as a function of E. The X- and B-state intensities remain in a nearly constant ratio, while the A state begins with very low intensity relative to X and B but increases by more than a factor of 2 over the range of E. The relative vibrational populations within a given electronic state are E-independent within error, with a slight apparent deviation ...
TL;DR: In this article, the temperature dependence of the valence-band emission from the surface of molybdenum has been studied with ultraviolet photo-emission spectroscopy.
TL;DR: The electron affinities of allyl, allyl-d5, 2-methylallyl, and 2methylallyallyl-d7 radicals have been determined from the 351 nm photoelectron spectra of the allylic anions as mentioned in this paper.
Abstract: The electron affinities of allyl, allyl-d5, 2-methylallyl, and 2-methylallyl-d7 radicals have been determined from the 351 nm photoelectron spectra of the allylic anions. The ions were prepared in a cooled helium flow reactor by the reaction of O- with the corresponding propene. The electron affinities found for the radicals listed above are 0.481 ± 0.008, 0.464 ± 0.006, 0.505 ± 0.006, and 0.493 ± 0.008 eV, respectively. Extensive vibrational structure is observed in all the spectra, as the CCC bending and symmetric stretching modes are activated upon photodetachment. Vibrational frequencies for these modes are obtained for all of the radicals. A second harmonic of an asymmetric CH2 rocking mode is observed in the spectra of the allyl, allyl-d5, and 2-methylallyl anions. Hot bands are used to determine the CCC bending frequencies in the allylic anions. Photoelectron angular distributions were measured for the allyl and 2-methylallyl anions. The photoelectron spectrum of allyl anion is calculated using a m...
TL;DR: In this paper, Kuttel et al. measured the spatial distribution of the NEA peak for the surface exposed surface by angle resolved UPS and showed the link between NEA property and the band bending of the (100) surface is elucidated by photoemission spectroscopy.
TL;DR: In this article, a collision-energy-resolved Penning ionization electron spectroscopy was used to make an assignment for the lowest π orbital in the ultraviolet photoelectron spectrum.
Abstract: Penning ionization of thiophene, furan, and pyrrole upon collision with He*(23S) metastable atoms was studied by collision-energy-resolved Penning ionization electron spectroscopy. A strong negative collision energy dependence of the partial ionization cross sections was observed for π bands. This tendency was used to make an assignment for the lowest π orbital in the ultraviolet photoelectron spectrum. In the studied collision energy range, the interaction potentials between He*(23S) and target molecules were found to be anisotropic, which is consistent with calculated interaction potential curves. For the out-of-plane directions, attractive interactions were found around the π orbital region. For the in-plane directions, repulsive interactions were found around the σCH orbital region and the sulfur atom of thiophene, while attractive interactions were found around the oxygen atom of furan. In the Penning ionization electron spectrum of pyrrole and thiophene, a satellite band was found to be associated w...
TL;DR: In this paper, the surface chemistry of S-passivated GaAs(001) was investigated by studying this surface after passivation and after several subsequent annealings, and it was shown that gallium dimers appeared after annealing to 520 \ifmmode^\circ\else\textdegree\fi{}C due to sulfur desorption.
Abstract: We have investigated the surface chemistry of (${\mathrm{NH}}_{4}$${)}_{2}$S-passivated GaAs(001) by studying this surface after passivation and after several subsequent annealings. We have used ultraviolet photoemission spectroscopy (UPS) at a near-normal takeoff angle and at a takeoff angle of 70\ifmmode^\circ\else\textdegree\fi{}. We have also used, in the same ultrahigh-vacuum chamber, reflectance anisotropy spectroscopy, which probes the optical transitions due to surface dimers, and therefore provides useful information for the interpretation of core-level spectra. We find that gallium dimers appear after annealing to 520 \ifmmode^\circ\else\textdegree\fi{}C due to sulfur desorption. At the same stage, there appears in the corresponding 3d core-level spectrum a surface component lying at a relative binding energy of -0.32 eV with respect to the volume contribution. Arsenic dimers appear after annealing to 360 \ifmmode^\circ\else\textdegree\fi{}C, following the desorption of excess arsenic. In the same way, there appears in the arsenic 3d core-level spectrum a component at a relative binding energy of -0.28 eV. After desorption of the passivating overlayer the gallium-terminated part of the surface is essentially covered with sulfur. These sulfur atoms are dimerized, and contribute to a line in the reflectance anisotropy spectrum. At this same stage, the arsenic-terminated one is covered with excess arsenic. Unlike what was believed previously from UPS analysis, As-S chemical bonds are situated only in the passivating overlayer, which contains no gallium atoms. Comparison of the core-level spectra as a function of takeoff angle shows that the progressive desorption of this overlayer produces a change of its morphology. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, carbon fullerene molecules doped with nitrogen atoms were synthesized using laser ablation of graphite in a heated nitrogen gas, and the presence of nitrogen in the product was confirmed by isotope labelled experiments using X-ray photoemission spectroscopy measurements showed the nitrogen 1s level at 400.7 eV.
Abstract: Fullerene molecules doped with nitrogen atoms were synthesized using laser ablation of graphite in a heated nitrogen gas. Laser desorption/ionization time-of-flight and Fourier transform mass spectroscopic studies revealed the presence of ions (m = 60, 70, etc) as well as pure carbon fullerene ions . The presence of nitrogen in the product was confirmed by isotope labelled experiments using . X-ray photoemission spectroscopy measurements showed the nitrogen 1s level at 400.7 eV.