An NEXAFS investigation of the reduction and reoxidation of TiO2(001)

Lusvardi, Victor S.; Barteau, Mark A.; Chen, J.G.; Eng, Joseph; Frühberger, Bernd; Teplyakov, and Andrew V.

doi:10.1016/s0039-6028(97)00740-1

Cited by 176 publications

(178 citation statements)

References 56 publications

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“…Data reduction was performed in the Athena module of the IFEFFIT code. O K-edge absorption spectra were acquired in fluorescence yield and were calibrated by applying a linear transformation to the energy axis to align the spectrum obtained from a TiO 2 (anatase) standard to a published reference 28 . The absolute energy calibration of the emission x-ray spectrometer was determined with reference to the Zn L 2 , 3 emission lines from a zinc metal standard.…”

Section: Experimental Methodsmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic-acidcoated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic-acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe Ledge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic-acid-coated sample. However, O K-edge absorption spectroscopy observed a ~0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase, and exert an effect on the global electronic and optical properties of the material.This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO 2 .

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Section: Experimental Methodsmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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“…The electrons in the d-orbitals and those in the ligand repel each other by means of electrostatics repulsion between charges. It implies that the delectrons closer to the ligand present higher bond energy than the others resulting in d-orbital energy splitting (t 2g and e g ) [33] yielding larger separations at higher oxidation states (see figure 6). Figure 7 shows the XA spectra collected in TEY of TiN x films produced at different temperatures under the presence of NH 3 in the CVD reactor.…”

Section: Nexafs Analysismentioning

confidence: 99%

Exploring the incorporation of nitrogen in titanium and its influence on the electrochemical corrosion resistance in acidic media

et al. 2016

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The role of the nitrogen incorporation into titanium, its chemical nature, the location in the titanium lattice and its electrochemical performance were investigated by a combination of several spectroscopy and microscopy techniques using samples prepared by CVD of NH 3 at different temperatures and successive electrochemically tested in 1 M of HClO 4 . We found that nitrogen is incorporated in either the interstitial or substitutional site of the lattice depending on the preparation temperature modifying strongly its corrosion resistance which was ascribed to the N 2p hybridization with the Ti 3d orbitals. It was found that at low temperature the N 2p orbitals were more likely to hybridize with Ti 3d -t 2g orbitals while higher temperature favours the hybridization with the Ti 3d -e g orbitals. This is responsible for the corrosion resistance shown by the samples prepared at higher temperature.

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“…Oxidative and reductive processing of metal oxides such as TiO 2 certainly has impact on the electronic structure, which can be measured for example with NEXAFS spectroscopy [16]. Thermal oxidation of a 125 nm thick pulsed laser deposited blue, non-stoichiometric WO 3-δ film turns the color from blue to yellow [13].…”

Section: Surface and Sub-surface Studies On Tungsten And Iron Oxide Pmentioning

confidence: 99%

Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation

Bora

Thieß

et al. 2013

Journal of Electron Spectroscopy and Related Phenomena

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Energy research is to a large extent materials research, encompassing the physics and chemistry of materials, including their synthesis, processing towards components and design towards architectures, allowing for their functionality as energy devices, extending towards their operation parameters and environment, including also their degradation, limited life, ultimate failure and potential recycling. In all these stages, xray and electron spectroscopy are helpful methods for analysis, characterization and diagnostics for the engineer and for the researcher working in basic science. This paper gives a short overview of experiments with x-ray and electron spectroscopy for solar energy and water splitting materials and addresses also the issue of solar fuel, a relatively new topic in energy research. The featured systems are iron oxide and tungsten oxide as photoanodes, and hydrogenases as molecular systems. We present surface and sub-surface studies with ambient pressure XPS and hard x-ray XPS, resonant photoemission, light induced effects in resonant photoemission experiments and a photo-electrochemical in-situ/operando experiment, and nuclear resonant vibrational spectroscopy (NRVS).

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An NEXAFS investigation of the reduction and reoxidation of TiO2(001)

Cited by 176 publications

References 56 publications

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Exploring the incorporation of nitrogen in titanium and its influence on the electrochemical corrosion resistance in acidic media

Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation

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