Showing papers on "Chemical state published in 2009"
TL;DR: A detailed description of the electronic properties, chemical state, and structure of uniform single and few-layered graphene oxide (GO) thin films at different stages of reduction is reported in this paper.
Abstract: A detailed description of the electronic properties, chemical state, and structure of uniform single and few-layered graphene oxide (GO) thin films at different stages of reduction is reported. The residual oxygen content and structure of GO are monitored and these chemical and structural characteristics are correlated to electronic properties of the thin films at various stages of reduction. It is found that the electrical characteristics of reduced GO do not approach those of intrinsic graphene obtained by mechanical cleaving because the material remains significantly oxidized. The residual oxygen forms sp3 bonds with carbon atoms in the basal plane such that the carbon sp2 bonding fraction in fully reduced GO is ∼0.80. The minority sp3 bonds disrupt the transport of carriers delocalized in the sp2 network, limiting the mobility, and conductivity of reduced GO thin films. Extrapolation of electrical conductivity data as a function of oxygen content reveals that complete removal of oxygen should lead to properties that are comparable to graphene.
1,646 citations
TL;DR: In this paper, an approach based on standard spectra from quality reference samples (Ni, NiO, Ni(OH)2, NiOOH), subtraction of these spectra, and data analysis that integrates information from the Ni 2p spectrum and the O 1s spectra is demonstrated.
Abstract: Quantitative chemical state X-ray photoelectron spectroscopic analysis of mixed nickel metal, oxide, hydroxide and oxyhydroxide systems is challenging due to the complexity of the Ni 2p peak shapes resulting from multiplet splitting, shake-up and plasmon loss structures. Quantification of mixed nickel chemical states and the qualitative determination of low concentrations of Ni(III) species are demonstrated via an approach based on standard spectra from quality reference samples (Ni, NiO, Ni(OH)2, NiOOH), subtraction of these spectra, and data analysis that integrates information from the Ni 2p spectrum and the O 1s spectra. Quantification of a commercial nickel powder and a thin nickel oxide film grown at 1-Torr O2 and 300 °C for 20 min is demonstrated. The effect of uncertain relative sensitivity factors (e.g. Ni 2.67 ± 0.54) is discussed, as is the depth of measurement for thin film analysis based on calculated inelastic mean free paths. Copyright © 2009 John Wiley & Sons, Ltd.
1,215 citations
TL;DR: In this paper, the role of Cu(II) ions and their associated structural features, such as chemical state and environment, in the 2-propanol oxidative decomposition under visible light and X-ray absorption fine structure (XAFS) measurements was investigated.
Abstract: We investigated the role of Cu(II) ions and their associated structural features, such as chemical state and environment, in the Cu(II)-grafted TiO2 photocatalyst by means of 2-propanol oxidative decomposition under visible light and X-ray absorption fine structure (XAFS) measurements. The 2-propanol decomposition activity under visible light (1 mW cm−2, 450−580 nm) was highly reproducible (three repetitions). The XAFS results indicated that the Cu(II) is incorporated in a distorted amorphous CuO-like structure, having a five-coordinated square pyramidal form. The distorted CuO formed clusters and attached to the TiO2 surface. The chemical state and environment of the Cu(II) ions were not changed, even after the photocatalytic oxidative reaction. Thus, Cu(II)-grafted TiO2 can be regarded as a stable photocatalyst. In addition, in situ XAFS measurements were performed under visible light in the presence of 2-propanol and absence of oxygen. Under these conditions, Cu(I) was generated. However, the latter co...
378 citations
TL;DR: In this article, a quantitative method of determining the cerium chemical state from the Ce 3D photoelectron spectra is described in detail, based on limited diffusion of the deposited Sn atoms into the ceria layer at low temperature.
107 citations
TL;DR: In this article, the Ba 0.5 Sr 0.8 Fe 0.2 O 3− δ (BSCF) cathode for solid oxide fuel cell has been prepared by glycine-nitrate combustion process.
101 citations
TL;DR: In this paper, an X-ray spectroscopy and theoretical study of the chemical state of several sulfur bearing minerals and a synthetic sodium sulfite sample was performed and compared to ab initio quantum chemical calculations.
Abstract: An X-ray spectroscopy and theoretical study of the chemical state of several sulfur bearing minerals and a synthetic sodium sulfite sample was performed. X-ray absorption and high-resolution Kα X-ray emission spectra were recorded and compared to ab initio quantum chemical calculations. A consistent interpretation of the chemical shift in the Kα emission spectra is obtained based on three different theoretical approaches (density functional theory, multiple scattering theory, and atomic multiplet theory). An analysis of the theoretical sulfur orbital population and valence bond is in agreement with the fluorescence energy position of the Kα lines even within the sulfide (S2−) series. It is shown that the Kα energy shifts can be used for a quantitative determination of the proportion of different sulfur species in heterogeneous samples.
93 citations
TL;DR: In this article, a quantitative analysis of catalyst layer degradation was performed with X-ray photoelectron spectroscopy (XPS), and the surface concentrations of carbon, fluorine, oxygen, sulfur and platinum on the catalyst layer surface were measured before and after fuel cell operation, and the different chemical states of carbon and platinum were identified.
83 citations
TL;DR: The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth as mentioned in this paper.
Abstract: The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by statistical analysis of the relevant TEM data. EXAFS measurements at the Ag K-edge have unambiguously disclosed the presence of Ag species in the final product, identifying their chemical state as well as the most probable lattice environment around them with a reasonably high level of confidence. The extensive sample knowl...
82 citations
TL;DR: In this paper, temperature-dependent x-ray photoelectron spectroscopy was used to investigate local chemical states and thermal stabilities of N dopants in ZnO:N film.
Abstract: Local chemical states and thermal stabilities of N dopants in ZnO:N film are investigated by temperature-dependent x-ray photoelectron spectroscopy. Different types of N local states are detected, including N2 molecules occupying O sites [(N2)O], –NO species, substitutional N atoms in O- and N-rich local environments (α- and β-NO). Compared to the β-NO, the α-NO shows a better thermal stability up to 723 K. However, the transformation from α-NO acceptor to undesirable (N2)O donor occurs above 743 K. The variation of N local states also affects Zn and O binding energies. Photoluminescence studies indicate the shallow acceptor nature of α-NO.
76 citations
TL;DR: In this article, different sets of N-doped TiO2 thin films have been obtained by changing the preparation conditions during the deposition, and some relationships have been established between these film properties and their visible light photoactivity.
Abstract: N-doped TiO2 thin films have been prepared by plasma enhanced chemical vapor deposition and by physical vapor deposition by adding nitrogen or ammonia to the gas phase. Different sets of N-doped TiO2 thin films have been obtained by changing the preparation conditions during the deposition. The samples have been characterized by X-ray diffraction, Raman, UV−vis spectroscopy, and X-ray photoemission spectroscopy (XPS). By changing the preparation conditions, different structures, microstructures, and degrees and types of doping have been obtained and some relationships have been established between these film properties and their visible light photoactivity. The N1s XP spectra of the samples are characterized by three main features, one tentatively attributed to Ti−N (i.e., nitride with a binding energy (BE) of 396.1 eV) and two others with BEs of 399.3 and 400.7 eV, tentatively attributed to nitrogen bonded simultaneously to titanium and oxygen atoms (i.e., Ti−N−O like species). By controlling the deposit...
63 citations
TL;DR: In this paper, the electrochemical stability of Mn oxide is mainly determined by its microstructure; the more fibrous (or porous) oxide had a greater durability against cyclic charge-discharge.
TL;DR: Gadolinia-doped Ceria (Ce0.9Gd0.1O1.95) was prepared by conventional solid state synthesis and found to be single phase by room temperature X-ray diffraction (XRD) as discussed by the authors.
TL;DR: To understand the effect of transition-metal-based additives added to reactive hydride composites, the chemical state and changes during the reaction as well as the microstructural distribution were investigated using x-ray absorption near-edge structure (XANES) spectroscopy and anomalous small-angle x-rays scattering (ASAXS).
Abstract: Reactive hydride composites (RHCs) are very promising hydrogen storage materials for future applications due to their reduced reaction enthalpies and high gravimetric capacities. At present, the materials' functionality is limited by the reaction kinetics. A significant positive influence can be observed with addition of transition-metal-based additives. To understand the effect of these additives, the chemical state and changes during the reaction as well as the microstructural distribution were investigated using x-ray absorption near-edge structure (XANES) spectroscopy and anomalous small-angle x-ray scattering (ASAXS). In this work, zirconium- and vanadium-based additives were added to 2LiBH4–MgH2 composites and 2LiH–MgB2 composites and measured in the vicinity of the corresponding absorption edge. The measurements reveal the formation of finely distributed zirconium diboride and vanadium-based nanoparticles. The potential mechanisms for the observed influence on the reaction kinetics are discussed.
TL;DR: The mechanism for nitrogen including the structure of carbon nanofibers through the catalysis was discussed on the basis of the results.
Abstract: Carbon nanofibers containing a range of nitrogen contents of 1−10 atom % were directly synthesized by catalytic chemical vapor deposition over nickel-based catalysts at 350−600 °C using acetonitrile and acrylonitrile. The nitrogen content was controlled by careful choice of the reaction conditions. The N-doped carbon nanofibers showed herringbone structure with 20−60 nm diameter. X-ray photoelectron spectroscopy was applied to examine the chemical state of nitrogen in carbon nanofibers. Structural features of N-doped carbon nanofibers were examined in X-ray diffraction and electron microscopy. The mechanism for nitrogen including the structure of carbon nanofibers through the catalysis was discussed on the basis of the results.
TL;DR: In this paper, the role of fluoride ion, the crystallinity of the anodic oxide, and the chemical state of an as-anodized TiO2 nanotubes were investigated.
TL;DR: An experiment to determine the electronic and chemical states of Cu in a ZnO crystal was performed using Hall measurement, X-ray photoelectron spectroscopy and low-temperature photoluminescence and Cu atoms showed different behaviors in theZnO matrix as a function of oxygen gas pressure.
TL;DR: In this article, in situ X-ray absorption spectroscopy (XAS) and Xray photoelectron spectrograms (XPS) were used to characterize Pd1−x nanoparticles submitted to hydrogen reduction and posterior H2S sulfidation at 150 or 300 °C.
Abstract: PtxPd1−x (x = 1, 0.7, or 0.5) nanoparticles submitted to hydrogen reduction and posterior H2S sulfidation at 150 or 300 °C were characterized by in situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The in situ XAS measurements allowed monitoring of short-range order changes around the Pt atoms induced by the thermal processes. The surface sensitivity and atom specific characteristics of XPS provided additional information about the chemical state of the atoms present in the outermost layers of the nanoparticles. Our experiments also indicate a Pd migration toward the surface of the nanoparticles driven by the thermal processes. We observed that the reduction process is necessary prior to the occurrence of any sulfur reaction and that the number of chemisorbed sulfur atoms is directly proportional to the quantity of Pd atoms.
TL;DR: The surface electron accumulation layer, surface structure, and surface chemical states of a-plane and c-plane InN epitaxial films were investigated in this paper, where electrical measurements indicated electron accumulation layers on the surface of both the InN films.
Abstract: The surface electron accumulation layer, surface structure, and surface chemical states of a-plane (nonpolar) and c-plane (polar) InN epitaxial films were investigated. Electrical measurements indicated electron accumulation layers on the surface of both the InN films. Angle-resolved x-ray photoelectron spectroscopy (XPS) measurements indicated a strong band bending at both surfaces, thus confirming the surface electron accumulation. Further XPS analysis of the near-surface chemical states indicated an In adlayer at the surface of c-plane InN and an oxygen adsorbed layer on the a-plane InN. These results suggest different ad-layers to cause the surface electron accumulation on c-plane and a-plane InN.
TL;DR: In this article, high-resolution XANES and PES spectra of N 1s reveal the chemical states of N dopants and give a direct observation of nitrogen location in the ZnO films.
Abstract: X-ray absorption near-edge spectroscopy (XANES) and photoelectron spectroscopy (PES) with synchrotron radiation have been applied to investigate the structure and chemical states of nitrogen atoms in ZnO:N films with different annealing temperatures. The high-resolution XANES and PES spectra of N 1s reveal the chemical states of N dopants and give a direct observation of nitrogen location in the ZnO films. The results indicate that only the nitrogen atoms incorporated substitutionally at O sites act as acceptors, and contribute to the p-type characteristic of the ZnO:N film.
TL;DR: In this paper, the compositions of thin Ni-Si films and the chemical states of elements are analyzed by means of X-ray photoelectron spectroscopy (XPS), in view of Pretorius' effective heat of formation (EHF) model.
Abstract: Binary component Ni-Si films of different compositions are fabricated on AISI 304L stainless steels by means of ion-beam sputter (IBS) deposition. The compositions of the thin films and the chemical states of elements are analysed by means of X-ray photoelectron spectroscopy (XPS). The phase formation is studied and discussed in view of Pretorius' effective heat of formation (EHF) model. The proportions of the resulting phases can then be deduced. The electronic structure for the various compositions is also qualitatively investigated from the XPS valence band spectra, suggesting the bonding changes from predominating metallic to covalent bonding in Ni-Si systems when Si content increases.
TL;DR: The change of the chemical states of inorganic oxoanion salts by low-energy single atomic projectiles, high-energy cluster ion beams, and mixed 0.2 kV Ar(+) and 10 kV C(60)(+) are presented.
Abstract: The change of the chemical states of inorganic oxoanion salts by low-energy single atomic projectiles (0.5 kV Ar+), high-energy cluster ion beams (10 kV C60+), and mixed 0.2 kV Ar+ and 10 kV C60+ are presented. Although the sputtering conditions of C60+ and C60+–Ar+ mixed sputtering used in this work provide more accurate results for profiling organic films than Ar+ sputtering, the difference in profiling inorganic materials is not as dramatic. For inert oxoanions like carbonate and phosphate, both Ar+ and C60+sputtering cause unappreciable sputter-induced chemical transformation to the remaining surface. For reactive oxoanions like nitrate, perchlorate, chlorate, and chlorite, although C60+ yields slightly better results than Ar+ sputtering due to the thinner disturbed layer, all the ion beams altered the chemical state significantly. As a result, none of these techniques can be used to provide true information below the surface. For intermediate oxoanions like nitrite and thio-S in thiosulfate, C60+ yields slightly better results than Ar+ sputtering. However, for sulfonate and the core-S in thiosulfate, C60+ causes more sputter-induced chemical transformation than Ar+ sputtering.
TL;DR: In this paper, the photoluminescent (PL) p-type 6H porous silicon carbides (PSCs) were annealed in Ar and vacuum conditions.
TL;DR: In this paper, chemical properties of the lithiated graphite surfaces during deposition using X-ray photoelectron spectroscopy and low-energy ion scattering spectrographs were investigated.
TL;DR: In this article, the structure, surface morphology, chemical state, optical and electrical properties of transparent conductive ZnO (ZMO) thin films were studied, and a minimum resistivity of 7.9 × 10−4 Ω cm was obtained with a carrier mobility of 27.3 cm2 V−1 s−1 and a carrier concentration of 3.1 × 1020 cm−3.
Abstract: Molybdenum-doped ZnO (ZMO) transparent conductive thin films were prepared by dc reactive magnetron sputtering on glass substrates from metallic targets. The structure, surface morphology, chemical state, optical and electrical properties of ZMO films were studied. The XRD pattern confirmed that ZMO thin films were polycrystalline with the hexagonal crystal structure, and the surface morphology measured by AFM demonstrated that the surface was smooth and compact. Chemical state analysis revealed that molybdenum atoms existed mainly in Mo6+ and Mo5+ ions but not in only single oxidation states. The minimum resistivity of 7.9 × 10−4 Ω cm is obtained with a carrier mobility of 27.3 cm2 V−1 s−1 and a carrier concentration of 3.1 × 1020 cm−3, and the average transmittance is more than 85% in the visible light region. The refractive index and extinction coefficient at the wavelength of 550 nm are 1.853 and 7.0 × 10−3, respectively. The energy bands increase from 3.37 eV to 3.8 eV with the increase in carrier concentrations and the carrier effective mass m* is 0.33 times the electron mass.
TL;DR: In this article, the structural and surface morphology of BZT thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the results showed that the random oriented BZTs thin film grown on Pt/Ti/SiO2/Si(1/0/0) substrate with a perovskite phase was crack-free.
TL;DR: In this article, the chemical states of U and Ce in the solid solutions of UO2 and CeO2 were studied using the X-ray photoelectron spectroscopy.
TL;DR: In this article, a dense and crack-free La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3−−− δ thin film has been prepared by RF magnetron sputtering.
TL;DR: In this article, angle-resolved hard x-ray photoelectron spectroscopy was used to investigate the chemical states of the interface of the Pt/Zn-polar ZnO, zinc diffusion into the Pt layer, forming PtZn and ZnPtO bonds.
Abstract: The interface structures and the chemical states between the Pt layer and polar-ZnO single crystal were investigated. Two-dimensional x-ray diffraction images revealed that Zn-polar ZnO had less mosaicity than the O-polar one. Angle-resolved hard x-ray photoelectron spectroscopy was used to investigate the chemical states of the interface. At the interface of the Pt/Zn-polar ZnO, zinc diffusion into the Pt layer, forming PtZn and ZnPtO bonds, was found. For the O-polar ZnO, in contrast, PtO was predominantly formed at the interface. Zinc diffusion prevented oxidization of the Pt layer and affected the mosaicity of the interface.
TL;DR: In this paper, the evolution of crystal structure and chemical state of the V-based hydrogen storage alloy (Ti0.32Cr0.46V0.22) during hydrogen absorption/desorption cycling was examined by X-ray diffraction (XRD) and Xray photoelectron spectroscopy (XPS).
TL;DR: In this paper, a case study on the co-adsorption of halide anions and cationic organic molecules is presented, where the phase behavior at the interface crucially depends on both their particular redox-state and the surface concentration of the halide counter ions.
Abstract: Charged organic adsorbates play an important role in a number of electrochemical reactions, e.g. as additives for metal plating relevant for device fabrication in the semiconductor industry. Fundamental investigations are mandatory in order to acquire profound knowledge of the structural and electronic properties of these layers parallel and perpendicular to the surface, and to finally achieve a deeper mechanistic understanding of the kinetics of involved charge transfer reactions taking place at these complex metal/organic/electrolyte interfaces. A key structural motif of these interfaces consists in 'paired' (inorganic)anion/(organic)cation layers that can have an enormous stability even during an ongoing charge transfer reaction. In this contribution we present and discuss a selected case study on the co-adsorption of halide anions and cationic organic molecules that exhibit a pronounced redox activity. It will be demonstrated that their phase behavior at the interface crucially depends on both their particular redox-state and the surface concentration of the halide counter ions. The subtle balance between adsorbate-adsorbate and adsorbate-substrate interaction of the poly-cationic organic layer can be carefully controlled by potential dependent anion adsorption and desorption processes through the organic layer. This process can be followed by in situ high-resolution scanning tunnelling microscopy, while additional information about the structural and chemical state of the respective phase is obtained from in situ X-ray diffraction and ex situ photoelectron spectroscopy.