Binding Energy Region Research Articles

Anion photoelectron spectroscopy of VnOm− (n=4–15;m=0–2)

The anion photoelectron (PE) spectra of small mass-selected vanadium oxide clusters VnOm− (n=4–15; m=0–2) are measured at a fixed photon energy of 4.66 eV with the aid of a magnetic bottle photoelectron spectrometer. Cluster anions are generated in a pulsed laser vaporization cluster source. The electronic structure of VnOm− clusters is investigated as a function of size n and composition m with special regard to the increasing oxidation state. The addition of one or two oxygen atoms to the vanadium cluster core induces a change of the electronic structure in the near-threshold binding energy region below 2 eV. Main spectral features are contributed from the transition metal d-derived orbitals, whereas the oxygen 2p contribution induces a hybridization between vanadium and oxygen frontier orbitals in the entire series of the investigated clusters n=4–15. Generally, electron affinities and vertical detachment energies increase with increasing cluster size revealing size-dependent discontinuities. Furthermore, relative dissociation energies for different oxygen-loss channels from the parent VnOm− clusters are determined from thermochemical cycles, and first insights into the stability patterns of neutral and negatively charged vanadium oxide clusters are provided.

Interference effects between2pphotoionization and resonant Auger decay channels at2s−1np(n=4,5)inner-shell resonances in Ar

The electron spectrum of Ar has been studied in the binding energy region of the ${2p}^{\ensuremath{-}1}{3p}^{\ensuremath{-}1}\mathrm{np}$ states. These states are populated in direct $2p$ photoionization accompanied by the $3\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{np}$ shake-up transitions. In addition, at photon energies corresponding to the $2\stackrel{\ensuremath{\rightarrow}}{s}4p,5p$ excitations they gain intensity through the ${2s}^{\ensuremath{-}1}n\stackrel{\ensuremath{\rightarrow}}{p}{2p}^{\ensuremath{-}1}{3p}^{\ensuremath{-}1}\mathrm{np}$ resonant Auger decay channels. The two channels can interfere, leading to changes in the intensities of the Ar $2p$ photoelectron satellites. Experimental results are compared with the results of one-step calculations.

Chemical and microstructural characterisation of silicon-containing carbon films

The chemical and microstructural modifications of carbon films, induced by silicon incorporation during the film growth, were studied on films deposited by rf magnetron sputtering of a graphite-silicon target. Silicon incorporation produced Si–C bondings in the films and an increased defect density in the carbon matrix structure. Besides, increasing the silicon content resulted in a significant decrease of the π-plasmon loss peak intensity in the C1s binding energy region in the X-ray photoelectron spectra, along with a lineshape sharpening for the σ–s component of the valence band spectra. This specific electronic structure is best discussed in terms of σ–π system perturbations rather than in terms of an increased sp 3/sp 2 hybridisation ratio in the films.

Ab initio study of valence correlation satellites in photoelectron spectra of neon

Ab initio calculations of energies and widths of the valence correlation satellites in the binding energy region between 48 and 99 eV of the photoelectron spectrum of neon are presented. The results are compared with the high-resolution, synchrotron radiation excited valence photoelectron spectra recorded by Kikas et al. [ J. Electron Spectrosc. Relat. Phenom. 77 (1996) 241] using photon energies of 96 and 169 eV and with previous synchrotron radiation and conventional radiation studies. Our calculations allow a deeper insight in the regions where a bunch of states, different in spin and angular momentum, are concentrated, and add considerable information on assignment and width of several transitions. The theoretical spectrum calculated in the region between 74 and 94 eV compares quite well with the experimental one.

Comparison of hydrogen chemisorption rates and electronic structures of small Nb nAl − clusters: a photoelectron spectroscopic study

Photodetachment photoelectron spectroscopy experiments on Nb n Al − clusters have been carried out in a size range n=4 to 12 at 3.49 eV photon energy. The evolution of the electronic structure is discussed as a function of cluster size and composition. Electron affinities (EA) and vertical detachment energies are determined. One central point of this study is the direct comparison of the electronic structure of pure and Al-doped Nb n − clusters in the threshold binding energy region with regard to hybridization effects. Direct correlation between electronic structure and H 2 chemisorption rate constants reported by Nonose et al. [Chem. Phys. Lett. 164 (1989) 427], is found for n=5 to 8 and n>9.

Phase accumulation model analysis of quantum well resonances formed in ultra-thin Ag, Au films on W(1 1 0)

Series of quantum well states (QWS's) have been observed in photoemission spectra for the Ag/W(1 1 0) and Ag/Au/W(1 1 0) systems in a binding energy region lying outside of the substrate energy gap that is needed for full confinement of electronic waves in the adlayer. It is shown that the observed features can be described as the quantum well resonance states. An extended phase accumulation model has been applied for analysis of these states and their energy positions. It has been shown that a good correlation with experimental results can be reached when a phase shift is introduced into the model which is related to partial scattering of confined waves on the electronic states in region of QWS formation outside of the substrate energy gap. The resulting total phase shift obtained on the base of this approach correlates nicely with the experimental one for both investigated systems.

The fragmentation of CCl4 dications studied by Auger electron-ion coincidence experiments

The formation and decay of dication states of tetrachloromethane has been studied in an electron impact experiment by Auger electron-ion coincidence measurements. The fragmentation following the Cl2p ionization has been studied in three different binding energy regions of the dication between 33.5 and 48.5 eV. In the experimental data no bound stable or metastable CCl42+ states have been observed and the fragmentation pattern of the dications resulted to be strongly dependent on the state and geometry of the dication.

Comparative Study on the Electronic Structure of Arc-Discharge and Catalytic Carbon Nanotubes

Electronic structure of multiwall carbon nanotubes has been studied by X-ray emission and photoelectron spectroscopy. The measurements were performed for two samples synthesized by different methods such as arc-discharge graphite evaporation and catalytic decomposition of hydrocarbons on supported catalysts. X-ray spectra of the former sample were shown to be similar to those of the highly oriented pyrolytic graphite, while the C Kα spectrum of catalytic nanotubes exhibited an enhanced density of π occupied states and the C 1s line of sample expanded toward both lower and higher binding energy regions. The models incorporating pentagon−heptagon pair and sp3-hybridized atoms have been calculated by AM1 quantum-chemical method to reveal the influence of defects on the electronic structure of carbon nanotube. Carbon Kα and 1s lines were found to be practically unaffected by inserting pentagon and heptagon into the hexagonal network on diametrically opposite sides of tube. However, the changes observed in the...

Effect of Surface Composition of Electrochemically Codeposited Platinum/Molybdenum Oxide on Methanol Oxidation

The electrochemical codeposition method has been used to prepare a series of carbon (GC) electrodes with different atomic ratios of Pt to Mo. The advantage of this method is the mixing of metal and support on a microscopic level (atomic or molecular scale). That is, to disperse the Pt microparticles into the molybdenum oxide on a GC substrate. The electrode was prepared by scanning the electrode potential between 0.55 and −0.70 V vs. in potassium hexachloroplatinate, sodium molybdate, and 2.2 M sulfuric acid solution at a GC substrate using a scan rate of 20 mV/s. The scanning electron microscopy results show that the Pt and microparticles are uniformly dispersed on the GC electrode surfaces. In addition, the modified electrode exhibits electrocatalytic activity for the oxidation of methanol. Based on the catalytic properties, the optimal concentrations for the preparation of the composite electrode is 3.0 mM in and 300 mM of X-ray photoelectron spectroscopy (XPS) analyses indicate that the best Pt to Mo atomic ratio is in the range between 1.5 and 2.0. In addition, the XPS spectra present a broad peak in the Mo (3d) binding energy region revealing the existence of species as well as lower valence state and Finally, a reaction mechanism is suggested for methanol oxidation at this composite GC electrode. © 2001 The Electrochemical Society. All rights reserved.

Direct EELS observation of the oxidation states of Sm atoms in Sm@C2n metallofullerenes (74⩽2n⩽84)

The oxidation states of Sm atoms in various fullerene cages are directly investigated by electron energy-loss spectroscopy. The observed peak positions of the M45 edges of the Sm atom in Sm@C2n [2n=74, 78, 80, 82 (isomers I, III), 84 (isomers I, II, III)] are apparently shifted to the lower binding energy region in comparison with those of a trivalent Sm3+ in Sm2O3. The results indicate that the Sm atoms take +2 valence states irrespective of the fullerene cages. This observation is discussed based on a simple thermochemical cycle model. We also report that the Sm metallofullerenes have been converted to Sm carbide materials under a prolonged electron beam irradiation.

XPS and UPS studies on electronic structure of Li 2O

The adsorption behavior of H 2O on Li 2O was studied by X-ray photo electron spectroscopy (XPS) and ultraviolet photo electron spectroscopy (UPS). XPS and UPS spectra of Li 2O single crystals which were exposed to different pressure of H 2O vapor were observed. In O(1s) region, two peaks were observed and they were assigned to O(1s) in precipitated LiOH on the surface and O(1s) in Li 2O. After H 2O exposure, a peak broadening and an appearance of a new peak were observed at the higher binding energy region than O(1s) in Li 2O. They were attributed to surface −OH and H 2O molecule adsorbed on the surface. The adsorption behavior of H 2O was discussed from the observation of electronic structure in Li 2O surface.

Theoretical and experimental study of inner-valence-shell satellites above the double-photoionization threshold of argon

The Ar photoelectron lines located above the double-ionization threshold have been investigated both theoretically and experimentally. Their Auger decay, sorted in a coincidence experiment, is found to occur predominantly to the Ar2+(1D) final state. Calculations demonstrate that while some photolines can be labelled as 3s3p5(3P)nl, none of them can be described as 3s3p5(1P)nl because such a configuration is always weaker than doubly excited ones in the configuration-interaction (CI) description of the state. This is evidence of `second-order satellites', which we define as satellites dominated by a doubly excited configuration. The intensity of the photolines in the 45-58 eV binding energy region is qualitatively demonstrated to reflect correlation in the Ar(1S) ground state, and is related to the singly and doubly excited configurations in the CI development of the latter.

Oxygen adsorption on a ZrC(111) surface: angle-resolved photoemission study

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the adsorption state of oxygen on a ZrC(111) surface. Oxygen adsorbs dissociatively at room temperature forming a ( 3 × 3 )R30° overlayer at 0.4–0.8 L and a (1×1) overlayer for further exposure. The two-dimensional band structure of the O 2p-derived states is measured for the (1×1)-O surface in the two symmetry directions; 〈2 1 ̄ 1 ̄ 〉 (Γ̄M̄) and 〈01 1 ̄ 〉 (Γ̄K̄) directions of the ZrC(111) surface. It is found that the O 2p x , 2p y and 2p z -derived bands are formed at nearly the same binding energy region, indicating that the O 2p x , 2p y and 2p z orbitals should have an almost equal contribution to the chemisorption bonding on the ZrC(111) surface.

Threshold photoelectron spectroscopy in the inner-valence ionization region and photo-double ionization of SF6

The threshold photoelectron (TPE) spectrum of SF6 has been recorded over the photon energy range 25-140 eV using synchrotron radiation and a penetrating-field electron spectrometer. In addition, the photo-double ionization spectrum of SF6 has been obtained over the energy range 30.7-49.3 eV using the threshold photoelectrons coincidence technique. The TPE spectrum in the inner-valence ionization region is found to be significantly different to the conventional photoelectron spectrum in the same binding energy region. Indirect autoionization of neutral Rydberg and shape-resonance states of SF6 dominate the formation of the TPE spectrum. Inner-valence SF6+ ion states appear to play a major role in the formation of the SF62+ ion states. The onset of double ionization in SF6 was found to occur at 31.98±0.02 eV.

XPS determination of the forms of nitrogen in coal pyrolysis chars

The N Is spectra from four pulverized Australian coals and their chars produced by pyrolysis for 2 s at 1100°C and 1300°C in a pressurized furnace are evaluated, with particular reference to the binding energy region above 402 eV. The spectra for the feed coals were broadly similar to those reported previously for bituminous coals, in that pyrrolic nitrogen was the dominant functional form in each case. A minor component between 403 and 404.5 eV was assigned to ammonium nitrogen in liberated mineral matter. The N Is spectra for the chars were also broadly similar to those expected for pyrolysis under intermediate residence time conditions, in that the proportion of pyrrolic nitrogen was no more than half that for the feed coal. Intensity in the 402-404.5 eV region was more consistent with N-O species formed post-pyrolysis than similar species formed as intermediates during pyrolysis.

Angle-resolved photoemission study of Ni-intercalated1T−TiS2

Angle-resolved photoemission spectra have been measured to study the electronic structures of Ni intercalated layered compound ${\mathrm{Ni}}_{1/3}{\mathrm{TiS}}_{2}.$ The results have shown that some new bands appear in ${\mathrm{Ni}}_{1/3}{\mathrm{TiS}}_{2}$ and the dispersions of most other bands are strongly modified compared with ${\mathrm{TiS}}_{2}.$ It is clarified that the new band near the Fermi level ${(E}_{F})$ is the split-off state or the bonding state between the final states originating from the $|{d}^{1}{(t}_{2g})〉$ and $|{d}^{2}{(t}_{2g}{,e}_{g})Ḻ〉$ initial states, where $Ḻ$ stands for the $\mathrm{S}3p$ hole state. Another new band observed at \ensuremath{\sim}1 eV below ${E}_{F}$ is hardly dispersive and attributed to the $\mathrm{Ni}{3d}_{{z}^{2}}\ensuremath{-}\mathrm{Ti}{3d}_{{z}^{2}}$ bonding state. The $\mathrm{Ni}3d``{e}_{g}''\ensuremath{-}\mathrm{S}3p$ bonding states are observed in the larger binding energy region. Knowledge of hybridizations among the $3d$ states of the intercalant, $\mathrm{Ti}3d$ states, and $\mathrm{S}3p$ states are essential to interpret the physical properties of ${\mathrm{Ni}}_{1/3}{\mathrm{TiS}}_{2}.$

Electronic Structure and Optical Limiting Behavior of Carbon Nanotubes

Carbon nanotubes prepared by catalytic (CO) disproportionation were studied using TEM, XRD, UPS, XPS, and optical spectroscopies. In comparison with graphite, the carbon nanotubes show greater interplanar distance, smaller work function, steeper Fermi edge, negative core-level shift, and stronger plasma excitation. Their valence band is basically the same as that of graphite, with lower intensity in the binding energy region of 2--7 eV. The carbon nanotubes exhibit a strong optical limiting effect, superior to both carbon black and ${\mathrm{C}}_{60}$.

Absolute Surface Density of the Amine Group of the Aminosilylated Thin Layers: Ultraviolet−Visible Spectroscopy, Second Harmonic Generation, and Synchrotron-Radiation Photoelectron Spectroscopy Study

The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)) was treated with (3-aminopropyl)triethoxysilane (1), (3-aminopropyl)diethoxymethylsilane (2), and (3-aminopropyl)ethoxydimethylsilane (3) for 72 h in solution. Thickness of the aminosilylated film out of 1 increases rapidly, and it turns out to be around 100 Å in 72 h. Rather slow increase of the thickness is observed for 2, which produces the layers of 8 and 14 Å in 10 and 72 h, respectively. The reagent 3 produces the monolayers of constant thickness 7−8 Å during the whole span of the reaction. The aminosilane layer was allowed to react with 4-nitrobenzaldehyde to form an imine, and absorbance (Asurf) of the imine was recorded by UV−vis spectroscopy. The imine was hydrolyzed in a known volume of water to produce 4-nitrobenzaldehyde, and subsequently its absorbance was measured. Thus observed number of the aldehyde molecules is equivalent to the number of the imine molecules on the surface. With the known surface area of the substrates, the absolute surface density of the imine, that is, the reactive amine group on the surface, was calculated. At an early stage of the aminosilylation with 2, a surface density of 3.9 amine groups per 100 Å2 was measured. A relatively low value was observed for 3. It is also observed that 1 produces a multilayer with rough surface morphology, of which surface density increases sharply by the reaction time. Tilt angle of the imine was estimated from the Asurf and the absolute surface density. The angles vary among 23−47° depending on the reaction condition. Second harmonic generation of a laser light of 1064 nm was observed for the imine-formed substrates. X-ray photoelectron spectroscopy utilizing a synchrotron radiation source, in particular for the N(1s) binding energy region, confirmed the chemical transformation. Also, it is observed that the nitro group of the imine is cleaved by X-rays.

A photoabsorption, photodissociation and photoelectron spectroscopy study of C 2H 4 and C 2D 4

The absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of ethylene and deuterated ethylene have been measured from the ionisation threshold to 500 Å using a double ion chamber and monochromated synchrotron radiation. High resolution photoelectron spectra of the same molecules have been recorded using HeI and HeII radiation, and detailed analyses have been made of the vibrational structure exhibited in the X 2B 3u, A 2B 3g, B 2A g, C 2B 2u and D 2B 1u photoelectron bands. In the inner valence binding energy region the HeII excited spectrum shows several satellite features which are due to configuration interaction effects. The photoabsorption spectra display extensive vibrational structure extending from the ionisation threshold to approximately 630 Å. With the aid of the high resolution photoelectron spectra, many of these absorption features have been arranged into vibrational progressions associated with Rydberg states. Tentative assignments for some of these states have been proposed based upon an assessment of terms values and quantum defects. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining wavelength regions.

Quasiparticle energy bands of transition-metal oxides within a model GW scheme

We calculate the quasiparticle band structure of NiO and ${\mathrm{CaCuO}}_{2}$ by using a model self-energy correction which approximates closely the GW method of Hedin. We obtain energy gaps and magnetic moments in agreement with experiment. For NiO, our results agree with integrated and angle-resolved photoemission experiments in the low binding energy region. The spectral distributions of O 2p and Ni 3d states are discussed, in relationship with the available experimental data. Our results demonstrate that the addition of self-energy corrections to local-spin-density band calculations provides a meaningful description of many aspects of the electronic states of transition-metal oxides. As expected, the satellite structures observed in photoemission experiments are not found in our calculations.