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This paper aimed to reveal the effects of chemisorbed oxygen species on selective catalytic oxidation applied for [H.sub.2]S removal. A sequence of thermal treatments were conducted on [V.sub.2][O.sub.5]/Ti[O.sub.2] samples to prepare catalysts that possess different distributions of oxygen species. Characterization by X-ray photoelectron spectroscopy enabled a distinction among three different chemisorbed oxygen species: [O.sup.-], [O.sub.2.sup.2-], and [O.sub.2.sup.-]. In addition, the dominance of the [O.sup.-] species, which is a very reactive oxygen species for catalytic oxidation reactions, was observed when the catalyst was exposed to 5% [O.sub.2]/[N.sub.2] gas at the low temperature of 30 [degrees]C. It was also found that the N400A30 with the highest ratio of [O.sup.-] species was superior to others at converting [H.sub.2]S into elemental sulfur over the whole range of temperatures: the best S yield of N400A30 was 85% at 130 [degrees]C. These results are promising, as thermal treatments for oxygen adsorption were adopted for the first time to improve the catalytic activity of [H.sub.2]S removal by modulating the proportion of highly reactive [O.sup.-] species. Key words: chemisorbed oxygen species, [V.sub.2][O.sub.5]/Ti[O.sub.2] catalysts, thermal treatments for oxygen adsorption, catalytic oxidation for [H.sub.2]S removal, highly reactive [O.sup.-] species, 1. Introduction Sustainable and renewable energy sources have been intensively investigated as means of meeting the ever-increasing demand for clean energy to realize carbon neutralization against climate change (.1,2) One [...]

Harnessing the carrier wave of light as an alternating-current bias may enable electronics at optical clock rates.sup.1. Lightwave-driven currents have been assumed to be essential for high-harmonic generation in solids.sup.2-6, charge transport in nanostructures.sup.7,8, attosecond-streaking experiments.sup.9-16 and atomic-resolution ultrafast microscopy.sup.17,18. However, in conventional semiconductors and dielectrics, the finite effective mass and ultrafast scattering of electrons limit their ballistic excursion and velocity. The Dirac-like, quasi-relativistic band structure of topological insulators.sup.19-29 may allow these constraints to be lifted and may thus open a new era of lightwave electronics. To understand the associated, complex motion of electrons, comprehensive experimental access to carrier-wave-driven currents is crucial. Here we report angle-resolved photoemission spectroscopy with subcycle time resolution that enables us to observe directly how the carrier wave of a terahertz light pulse accelerates Dirac fermions in the band structure of the topological surface state of Bi.sub.2Te.sub.3. While terahertz streaking of photoemitted electrons traces the electromagnetic field at the surface, the acceleration of Dirac states leads to a strong redistribution of electrons in momentum space. The inertia-free surface currents are protected by spin-momentum locking and reach peak densities as large as two amps per centimetre, with ballistic mean free paths of several hundreds of nanometres, opening up a realistic parameter space for all-coherent lightwave-driven electronic devices. Furthermore, our subcycle-resolution analysis of the band structure may greatly improve our understanding of electron dynamics and strong-field interaction in solids. Time- and angle-resolved photoemission spectroscopy reveals how Dirac fermions in the band structure of the topological surface state of Bi.sub.2Te.sub.3 are accelerated by the carrier wave of a terahertz-frequency light pulse., Author(s): J. Reimann [sup.1] , S. Schlauderer [sup.2] , C. P. Schmid [sup.2] , F. Langer [sup.2] , S. Baierl [sup.2] , K. A. Kokh [sup.3] [sup.4] , O. E. [...]

We report on an experimental approach that reveals crucial details of the composition of singlet-triplet mixed eigenstates in acetylene. Intersystem crossing in this prototypical polyatomic molecule embodies the mixing of the lowest excited singlet state ([S.sub.1]) with 3 triplet states ([T.sub.1], [T.sub.2], and [T.sub.3]). Using high-energy (157-nm) photons from an [F.sub.2] laser to record excited-state photoelectron spectra, we have decomposed the mixed eigenstates into their [S.sub.1], [T.sub.3], [T.sub.2], and [T.sub.1] constituent parts. One example of the interpretive power that ensues from the selective sensitivity of the experiment to the individual electronic state characters is the discovery and examination of destructive interference between two doorway-mediated intersystem crossing pathways. This observation of an interference effect in nonradiative decay opens up possibilities for rational coherent control over molecular excited state dynamics. Decomposition mixed eigenstates | Nonradiative decay interference | Photoelectron spectroscopy

Photoelectron spectroscopy and ab initio calculations are used for studying the production and characterization of a unique boron oxide cluster, [B.sub.4][O.sub.2.sup.2-]. The high stability of [B.sub.2][(BO)>sub.2.sup.2-] has shown that it might exist as a viable building block in the condensed phase.

He I photoelectron (PE) spectroscopy is employed to characterize [3] and [5] ladderanes obtained by way of template-controlled syntheses conducted in the organic solid state. The results provide a first correlation with X-ray crystallographic structure data.

Cyclopentadienyl dialuminum with a half sandwich structure is prepared in a pulsed laser ablation cluster beam source and identified with a time of flight photoionization mass spectrometer. The high resolution electron spectrum of this complex is obtained using pulsed field ionization zero electron kinetic energy photoelectron spectroscopy.

The electronic structures at the silicon/molecule interface are studied by using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe methods. The results have highlighted the utilization of organic molecule surface grafting as a means to tune the electronic properties of semiconductors and to achieve controllable modulation of electronic characteristics in small semicontrollable devices.

The electronic and geometric structural characterization of a novel species, diaceto disulfide C[H.sub.3]C(O)OSSOC(O)C[H.sub.3] obtained through the heterogeneous reaction between sulfur monochloride and silver acetate is presented. The optimization and vibrational analysis showed the molecules to prefer C=O bonds cis to S-O bonds.

Ultraviolet photoelectron spectroscopy (UPS) is used to study the electronic structures and substituent effects of o-, m-, and p-iodonitrobenzene and the observed bands are interpreted on the basis of empirical arguments and theoretical calculations. The correlation between substituent effects and the relative reactivities of the iodonitrobenzenes is described by the investigation of [pi]- and n-orbital ionization potentials.

Negatively charged sodium auride clusters, [Na.sub.n][Au.sub.n.sup.-] (n=1-3) were investigated experimentally using photoelectron spectroscopy and ab initio calculations. The results showed well-resolved electronic transitions at several photon energies and very large band gaps were observed in anion clusters indicating that the corresponding neutral clusters are stable closed-shell species.

The photoionization and photoelectron spectroscopy of pure He droplets were investigated at different photon energies. It was seen that at source temperature below 16 K the photoelectron images are dominated by fast electrons produced through direct ionization with a small contribution from very slow electrons arising from an indirect mechanism.

The solvation of sodium aggregates in small water clusters was investigated by photoelectron spectroscopy (PES) of [Na.sup.-.sub.2] [([H.sub.2]O).sub.n]. It was found that the [Na.sup.-]- [Na.sup.}[([H.sub.2]O).sup.-.sub.n]- type electron state grows with increasing cluster size which may be due to the solvation of [Na.sup.-.sub.2] with ionization of the hydrated Na.

The measurement and analysis of x-ray photoelectron spectra (XPS) of as-grown and annealed [Ge.sub.33][As.sub.12][Se.sub.55] films compared with bulk material are described. The results have shown that, while thermal annealing is effective to move the film toward the bond structure of bulk glass, the simultaneous surface oxidation should be suppressed in order to achieve high quality films.

The synthesis of La C[O.sub.3]OH microspheres is carried out by a hydrothermal reaction between La[(NO.sub3).sub3].6H.sub.2O and urea. The structures of these microspheres are studied with the help of spectroscopy and photoluminence.

Photoelectron spectroscopy (PES) and density functional theory (DFT) are used to study the formation of intermediate phenyl-copper metal complexes [[[C.sub.6][H.sub.5][Cu.sub.m]].sup.-] (m = 1-3). The results have shown that the complex [[[C.sub.6][H.sub.5][Cu.sub.2]].sup.-] is easy to generate than [[[C.sub.6][H.sub.5][Cu.sub.3]].sup.-] and [[[C.sub.6][H.sub.5]Cu].sup.-].

X-ray photoemission spectroscopy (XPS) is used to evaluate the nature of defects in polycrystalline [Bi.sub.4-x][La.sub.x][Ti.sub.3][O.sub.12] (BLT) thin films. The XPS data has shown a nominal valence state of bismuth lower than 3 and Ti cations are found to be in the 4 state.

A method is developed to measure effective work function of metal gate in contact with high-[kappa] dielectric. The effective work function of NiSi, N[i.sub.2]Si, and Sb-doped Si gate electrodes on high-[kappa] gate stack dielectric was found to be 4.4, 4.5-4.7, and 4.2 eV respectively.

The material and electrical modification of HF-based dielectrics at different annealing conditions and different Si incorporations is investigated. The X-ray photoelectron spectroscopy (XPS) results have indicated a great signature of the formation of a HF-silicate layer.

Anionic states of nucleic acid bases are involved in DNA damage by low-energy electrons and in charge transfer through DNA. Previous gas phase studies of free, unsolvated nucleic acid base parent anions probed only dipole-bound states, which are not present in condensed phase environments, but did not observe valence anionic states, which for purine bases are thought to be adiabatically unbound. Contrary to this expectation, we have demonstrated that some thus far ignored tautomers of adenine, which result from enamine-imine transformations, support valence anionic states with electron vertical detachment energies as large as 2.2 eV, and at least one of these anionic tautomers is adiabatically bound. Moreover, we predict that the new anionic tautomers should also dominate in solutions and should be characterized by larger values of electron vertical detachment energy than the canonical valence anion. All of the newfound anionic tautomers might be formed in the course of dissociative electron attachment followed by a hydrogen atom attachment to a carbon atom, and they might affect the structure and properties of DNA and RNA exposed to low-energy electrons. The new valence states observed here, unlike the dipole-bound state, could exist in condensed phases and might be relevant to radiobiological damage. The discovery of these valence anionic states of adenine was facilitated by the development of (i) an experimental method for preparing parent anions of nucleic acid bases for photoelectron experiments, and (ii) a combinatorial/quantum chemical approach for identification of the most stable tautomers of organic molecules. nucleic acid bases | photoelectron spectroscopy | tautomers | valente anion

Zero kinetic energy (ZEKE) photoelectron spectroscopy and photoionization efficiency measurements are used to determine the relative energies of several conformations of the tryptophol cation. The photoelectron spectra have revealed that structural changes upon ionization are dominated by interactions of the hydroxyl group with the changes of electronic structure in the aromatic system.

Femtosecond time-resolved photoionization and photoelectron spectroscopy are used to investigate the excited-state dynamics of the tert-butyl radical, t-[C.sub.4][H.sub.9]. Ab initio calculations of the electronic ground state and a number of electronically excited states are performed in order to understand the shapes and characters of the excited-state potential energy surfaces.

The atomic structure of amorphous and crystalline hafnium oxide (Hf[O.sub.2]) films was examined using X-ray diffractometry and Hf edge X-ray absorption spectroscopy. The valence band of Hf[O.sub.2] consists of three subbands separated from each other by ionic gaps, the upper subband is formed by O 2p, Hf 4f and Hf 5d states and the intermediate subband is formed by O 2s and Hf 4f states.

X-ray photoelectron spectroscopy (XPS) is employed to study the polyamide samples, which are modified by aluminum (Al) ions by filtered cathodic vacuum arc (FCVA), using with plasma immersion ion implantation (PIII) technique. The study reveals the chemical bond between implanted and deposited Al ions and the polyimide matrix, which is found to be extremely useful for the entire process.

High boiling solvent process was used to synthesize high quality ZnS, ZnS:[Mn.sup.2+], and ZnS:[Mn.sup.2+]/ZnS (core/shell) luminescent nanocrystals (NCs) and they were characterized by different spectroscopic methods. Highly monodisperse ZnS NCs were obtained by adding poly(ethylene glycol) to the reaction system and these ZnS NCs can be self-assembled into closely packed ultra-large range 2D arrays on the carbon-coated Cu grid.

A combination of photoluminescence, infrared and X-ray photoelectron spectroscopy is used to study the anodic decomposition of unsaturated Grignards at a hydrogenated silicon electrode, which result in the formation of polymers with broken bonds of the aliphatic precursors. The analysis reveals that the polymers can be highly contaminated by the attack of the ethynyl radicals, which can be avoided by using appropriate solvents, hence making it useful for applications.

A study is conducted to determine the interfacial changes of Hf[O.sub.2]/Si/n-GaAs gate stacks annealed at high temperatures. It is found that oxygen atom is likely to diffuse to the GaAs interface and form gallium and arsenic oxides, which might act as deep traps.

We describe self-assembly of ssDNA brushes that exploits the intrinsic affinity of adenine nucleotides (dA) for gold surfaces. The grafting density and conformation of these brushes is deterministically controlled by the length of the anchoring dA sequences, even in the presence of thymine nucleotides (dT). We produce and characterize brushes of model block-oligonucleotides, d([T.sub.m]-[A.sub.n]), with systematically varied lengths m and n of the thymine and adenine blocks [denoted d([T.sub.m]) and d([A.sub.n]), respectively]. The hairpin conformation, dominant for self-complementary d([T.sub.m]-[A.sub.n]) oligos in solution, is disrupted by the high preferential affinity of dA for gold surfaces. As a result, the d([T.sub.m]-[A.sub.n]) oligos adsorb as a brush of d(T) strands immobilized via the d(A) blocks. Quantitative analysis by FTIR spectroscopy and x-ray photoelectron spectroscopy (XPS) reveals a unique feature of DNA immobilization via d(A) blocks: The surface density of dA nucleotides is close to saturation and is nearly independent of d(A) block length. Accordingly, the lateral spacing (grafting density) of the d(T) blocks is determined by the length of the d(A) blocks. The d(T) blocks extend away from the surface in a brush-like conformation at a lateral spacing 2-3 times larger (a grafting density 5-10 times lower) than in analogous films immobilized via standard thiol linkers. This combination of brushlike conformation and low saturation grafting density is expected to increase the efficiency of DNA hybridization at surfaces. Therefore, immobilization via d(A) blocks offers a method of producing DNA brushes with controlled properties for applications in biotechnology and nanotechnology. FTiR | gold | immobilization | oligonucleotides | x-ray photoelectron spectroscopy

Measurements of the modification of a single damascene patterned ultralow-kappa (ULK) interlevel dielectric (ILD) structure are determined by modeling of the ion angular distribution function (IADF) in Ar/[O.sub.2] and Ar/[N.sub.2] discharges. It is proposed that the mechanism for modification of the porous interlevel dielectric (ILD) is dominated by the creation of reactive sites by ion impact under the present conditions.

An external bias is applied to two samples containing composite surface structures, while recording an XPS spectrum. Altering the polarity of the bias affects the extent of differential charging in domains that are chemically or electronically different to create a charge contrast. By utilizing this charge contrast, we show that two distinct silicon nitride and silicon oxynitride domains are present in one of the composite samples. Similarly, we use this technique to show that titanium oxide and silicon oxide domains exist as separate chemical entities in another composite sample.

Alkylamines (RC[H.sub.2]N[H.sub.2], R=H, C[H.sub.3], [C.sub.2][H.sub.5], [C.sub.3][H.sub.7], i-[C.sub.3][H.sub.7] were studied by dissociative photoionization by threshold photoelectron photoion coincidence spectroscopy. The optimized heats of formation of the ethyl and the propyl radical obtained indicate that their error bars were overestimated in previous measurements.

The undoped p-type copper indium diselenide (CuIn[Se.sub.2], CIS) layers grown by using a hot wall epitaxy (HWE) are studied by measuring their photocurrent (PC) spectra at different temperatures. The results have indicated that in undoped p-type CIS layers, the trapping center has limited the PC signal because of the native defects and impurities with decreasing temperature.

Temperature-programmed desorption (TPD), temperature-programmed low-energy ion scattering (TP-LEIS), and X-ray photoelectron spectroscopy (XPS) are used study the interaction of [O.sub.2] with small Pd particles (2-10 nm) supported on an alpha-[Al.sub.2][O.sub.3](0001) single crystal under ultrahigh vacuum (UHV) and high-pressure conditions. Results show that a low [O.sub.2] exposure (30L) at 500 K leads to surface oxygen adatoms on Pd nanoparticles supported on clean alpha-[Al.sub.2][O.sub.3](0001).

The influence of source conditions on vanadium-carbon cluster formation in methane-vanadium plasma is analyzed by photoelectron spectroscopy, which has revealed that the metal-carbon ratio has substantial influence over the cluster products. The experimental and computational results have shown that the V[C.sub.2] unit serves as a precursor in the growth of large metal-carbon clusters.

The investigation of the cysteine anion in the gas phase is reported. The cysteine anion exists as a hydrogen-bonded thiolate [[super -]SC[H.sub.2]CH(N[H.sub.2])C[O.sub.2]H] rather than a carboxylate [HSC[H.sub.2]CH(N[H.sub.2])C[O.sub.2.sup.-]] and the intramolecular O-H...[S.sup.-] hydrogen-bond strength in cysteine thiolate anion is estimated as 16.4 +- 2.0 kcal/mol.

The bipolar amphiphile 22-methoxydocosan-1-ol (H3C-O-(CH2)22-OH, MDO) and the monopolar amphiphle dicosyl methyl ether (H3C-(CH2)21-O-CH3, DME) were selectively synthesized for the first time as model compounds to elaborate the effect of a second polar group on the monolayer behavior by comparison with the corresponding alcohol docosan-1-ol (H3C-[CH2).sub.21-OH, DO). GIXD data show that the monolayers exhibit the phase sequence L2'-S at lower temperature and L2'-LS at higher temperature.

Thin films of metallophthalocyanine (MPc, M = Co, Ni) evaporated on reconstructed Au(001) substrate are investigated by using low energy electron diffraction (LEED) and ultraviolet photoelectron spectroscopy (UPS). The orbital-specific interaction observed in CoPc/Au(001) has pointed to the participation of the central metal atom to the bonding in addition to the interaction through [pi] electrons to the Pc ring.

Self-assembled monolayers (SAMs) prepared from fullerene derivatives of thiols/thiol esters/disulfides are analyzed in detail and the complications due to multilayer formations and head-to-tail assemblies are revealed. Several fullerene derivatives based on thiols, thiol acetates and disulfides are designed and synthesized to address the characterization requirements and these are described and delineated.

This article reviews the surface science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler--Natta polymerization. Under clean, ultrahigh vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler--Natta catalysts can be used to create a 'single-site' catalyst film with a surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler--Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a surface science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process. Ziegler--Natta

Neuromelanin (NM) isolated from the substantia nigra region of the human brain was studied by scanning probe and photoelectron emission microscopies. Atomic force microscopy reveals that NM granules are comprised of spherical structures with a diameter of [approximately equal to]30 nm, similar to that observed for Sepia cuttlefish, bovine eye, and human eye and hair melanosomes. Photoelectron microscopy images were collected at specific wavelengths of UV light between 248 and 413 nm, using the spontaneous-emission output from the Duke OK-4 free electron laser. Analysis of the data establishes a threshold photoionization potential for NM of 4.5 [+ or -] 0.2 eV, which corresponds to an oxidation potential of -0.1 [+ or -] 0.2 V vs. the normal hydrogen electrode (NHE). The oxidation potential of NM is within experimental error of the oxidation potential measured for human eumelanosomes (-0.2 [+ or -] 0.2 V vs. NHE), despite the presence of a significant fraction of the red pigment, pheomelanin, which is characterized by a higher oxidation potential (+0.5 [+ or -] 0.2 V vs. NHE). Published kinetic studies on the early chemical steps of melanogenesis show that in the case of pigments containing a mixture of pheomelanin and eumelanin, of which NM is an example, pheomelanin formation occurs first with eumelanin formation predominantly occurring only after cysteine levels are depleted. Such a kinetic model would predict a structural motif with pheomelanin at the core and eumelanin at the surface, which is consistent with the measured surface oxidation potential of the [approximately equal to]30-nm constituents of NM granules. free electron laser | oxidative stress | photoelectron imaging | substantia nigra | Parkinson's disease

Structural and electronic properties of pristine and lithium-intercalated, phenyl-capped aniline dimmers as a model for the lithium-polyaniline system were studied by photoelectron spectroscopy and quantum chemical calculations. It was found that the electronic structure of reduced and oxidized forms of oligoanilines is only weakly affected by isomerism.

Despite numerous experiments and static electronic structure calculations, the nature of hydrated-electron clusters, [([H.sub.2]O).sup.-.sub.n], remains poorly understood. Here, we introduce a hybrid ab initio molecular dynamics scheme, balancing accuracy against feasibility, to simulate vibrational and photoelectron spectra of [([H.sub.2]O).sup.-.sub.n], treating all electrons quantum-mechanically. This methodology provides a computational tool for understanding the spectra of weakly bound and supramolecular anions and for elucidating the fingerprint of dynamics in these spectra. Simulations of [([H.sub.2]O).sup.-.sub.4] provide quantitative agreement with experimental spectra and furnish direct evidence of the nonequilibrium nature of the cluster ensemble that is probed experimentally. The simulations also provide an estimate of the cluster temperature (T [approximately equal to] 150-200 K) that is not available from experiment alone. The 'double acceptor' electron-binding motif is found to be highly stable with respect to thermal fluctuations, even at T = 300 K, whereas the extra electron stabilizes what would otherwise be unfavorable water configurations. ab initio molecular dynamics | hydrated electron | photoelectron spectroscopy

The CO oxidation reaction on the smooth and defect-rich Ru(0001) surfaces prepared under high vacuum conditions are investigated by using thermal desorption spectroscopy (TDS). Reactive molecular beam scattering (RMBS) is applied to monitor the temporal behavior of the CO2 reaction yield and to analyze the influence of morphology on the reaction pathways.

The phenyl-lead metal complexes [[[Pb.sub.m]C6H5].sup.-] produced from the reactions between benzene and lead cluster formed by laser ablation on a lead solid sample are studied by photoelectron spectroscopy (PES) and density functional theory (DFT). Results reveal that the phenyl group binds perpendicularly on lead clusters through the Pb-C sigma bond and the complexes have a closed shell structure.

The synchrotron based vacuum ultraviolet-pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of ammonia (N[H.sub.3]) is measured in the energy range 10-12-12.12 eV using a room temperature N[H.sub.3] sample. It is demonstrated that the two-color IR-VUV-photoion depletion (PID) detection scheme is a valuable method for identifying the rotational nature of autoionizing Rydberg resonances.