On the determination of atomic charge via ESCA including application to organometallics

Sleigh, Christopher J.; Pijpers, A. P.; Jaspers, A.W.M.A.; Coussens, Betty; Meier, Robert J.

doi:10.1016/0368-2048(95)02392-5

Cited by 187 publications

(96 citation statements)

References 38 publications

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“…The O 1 s spectra show two peaks at 529.86 and 532.04 eV. The peak near 529.86 eV is attributed to metal oxides, 35,37,38 and that near 532.04 eV corresponds to the adsorbed oxygen. 31 The XPS data can be used to identify the species present on the surface, although estimation of fractional surface coverage would require deconvolution analysis of angle resolved XPS data.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Amrutha

Rao

Ramanathan

2018

J. Electrochem. Soc.

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Anodic dissolution of Zr in 10 mM HF was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. The surface state of the electrode was analyzed using X-ray photon spectroscopy, and the surface morphology was characterized using atomic force microscopy. EIS data acquired at multiple dc potentials were subjected to mechanistic analysis. Reaction mechanism analysis approach reveals that at least four intermediates are required to describe the observed results. The intermediates are likely to be Zr sub-oxides, oxyfluorides and ZrO 2 . The proposed mechanism successfully predicts the major features observed in polarization and impedance spectra. At low overpotentials, the fractional surface coverage of Zr 3+ species is higher than that of Zr 4+ species, and the electrochemical dissolution rate is higher than the chemical dissolution rate. As the overpotential increases, the surface is covered with Zr 4+ species and chemical dissolution rate becomes comparable to electrochemical dissolution rate. Although the surface is covered with Zr 4+ species at higher overpotentials, significant chemical and electrochemical dissolution processes continue to occur and hence Zr is not protected in acidic fluoride media under anodic conditions. © The Author Zirconium and alloys containing Zr are extensively used in the nuclear power industry as fuel cladding agents, in chemical industries as an alloying component, and in biomedical implants.1-4 The wide acceptance of this metal and its alloys is due to their superior mechanical strength, and high resistance toward corrosion, and H 2 embrittlement.5-8 These properties are due to the formation of a stable, protective passive film of ZrO 2 .9-11 Although Zr exhibits excellent corrosion resistance in most of the harsh environments, it readily dissolves in acidic fluoride media. 6,7,12,13 Earlier scientific reports on Zr dissolution are mostly based on conventional techniques, such as weight loss measurements, 14 measurement of volume of H 2 gas evolved, 7 and steady-state polarization techniques.15 Prono et al. 16 have analyzed the polarization of Zr in 0.12 M NaF + 7 M HNO 3 and proposed a seven-step mechanism comprising three competitive paths to describe the dissolution. This analysis was limited to the modeling of polarization data obtained at a single concentration. In our previous work, Zr anodic dissolution mechanism in the acidic fluoride medium was studied using the mechanistic analysis of current potential polarization data in various HF solutions.17 A mechanism containing two adsorbed intermediates and two dissolution steps, shown in Eq. 1, was proposed. The model successfully predicted the major characteristics of the polarization curves, and the results predicted that the chemical and the electrochemical dissolution steps were affected by the concentration of HF − 2 and HF, respectively. Anodic dissolution of other valve metals such as Ti 18,19 and Nb 20 have been characterized using potentiodynamic polarization and electrochemical imped...

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Section: Resultsmentioning

confidence: 99%

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Amrutha

Rao

Ramanathan

2018

J. Electrochem. Soc.

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“…The interaction coefficient, k, was taken as 19.6 for F 1s, from the empirical formula determined by Sleigh et al 44 The Madelung potential using the shortened bond lengths can be approximately described by a Coulombic interaction assuming each atom as a point charge in space (in this treatment, C 60 is taken as a single point charge of molecular radius). The point-charge model for the potential in eV on a given atom, i, can be described by…”

Section: Resultsmentioning

confidence: 99%

LiF Doping of C₆₀Studied with X-ray Photoemission Shake-Up Analysis

Turak

Zgierski

Dharma‐wardana

2017

ECS J. Solid State Sci. Technol.

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We report our investigation of the chemical doping mechanism induced by LiF interaction with fullerene thin films. High resolution Xray photoelectron spectroscopy of the C1s shake-up satellites and F1s main core level, supported by density functional calculations, suggest the formation of a charge transfer complex between covalent LiF monomers and dimers and C 60 . This interaction was observed in both LiF/C 60 and C 60 /LiF depositions, suggesting that some charge transfer complexation can occur in these systems even without dissociation. hydrogen storage materials, 5 and even antibacterial treatments. 6,7 Due to the rich electronic properties in the ground and excited states, C 60 is most widely used as an organic semiconductor. With the ability to act as both an electron acceptor and donor, it is a standard material in organic light emitting diodes, solar cells, transistors and Schottky diodes.The interface with the metal contacts play a crucial role in the effectiveness of organic semiconductors in device performance and stability.8 Introducing a thin buffer layer of LiF between an organic film and an Al cathode has been seen to dramatically enhance the energy-level alignment and stability of the interface.9-13 Additionally, alternating stacks of LiF and C 60 14 and LiF doped C 60 nanocomposite buffer layers 15,16 have been shown to have high conductivities and stability in OLEDs and OPVs. Several mechanisms have been proposed for these behaviors including chemical reactions, dipole alignment, tunneling, and LiF dissociation requiring the additional presence of Al. 17In this contribution, we present results showing that in the absence of Al, there is a charge transfer interaction between LiF and C 60 , leading to the formation of LiF••C 60 complexes without dissociation. Using the well-developed and described X-ray photoelectron shakeup structure of C 60 and the strong feature from F1s XPS core level, we see evidence of a direction independent interaction. The spectroscopic features can be described by the semi-covalent interaction of LiF monomers or dimers with C 60 using density functional theory. Coupled with XPS core level shift calculations, using approximate Madelung energy, the predicted Millikan charges and bond lengths give values that approximate the observed core level shifts. Additionally, the small transfer of charge to C 60 predicted by the modelling is consistent with the minimal impact on the shake-up satellites of the C1s of C 60 . ExperimentalThe samples were produced using a Kurt J. Lesker OLED cluster attached to an X-ray photoelectron spectroscopy tool. For deposition of C 60 , ∼5Å of LiF on 100 nm sputter deposited Au/Si was used z E-mail: turaka@mcmaster.ca as a substrate. For deposition of LiF, the substrate was 350Å of C 60 thermally deposited onto cleaned Si with native oxide. C 60 and LiF were thermally evaporated from home built crucible sources at an average rate of 1 Å/min and 2-3 Å/hr as measured by oscillating quartz crystal microbalance (Inficon XTM/2) respectively onto previ...

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“…51 However, the effect shown in Fig. 3 can also partly be explained by the formation of metallic Ti from TiCl 3 remainders, although this would not fit well with the Ti (III) species that we see at 457 eV (TiCl 3 2p 3/2: 458.5 eV 47 ). Thus, we repeated the measurement using Ti-doped NaAlH 4 previously cycled three times (desorbed at 125 • C and 0.1 mbar and rehydrided at 125 • C and 90 bar H 2 ).…”

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confidence: 82%

“…The lower energy component identified at 454.2 eV is straightforwardly assigned to Ti(0) (Ti metal 2p 3/2: 454.3 eV 46 ). The second one identified at 457 eV is too low for Ti(IV) (TiO 2 2p 3/2: 458.6 47 ) and too high for Ti(II) (TiO 2p 3/2: 455.9 eV 48 ), i.e. it does not fit with the two most common forms of Ti oxide.…”

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confidence: 95%

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

et al. 2014

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The reversibility of hydrogen sorption in complex hydrides has only been shown unambiguously for NaAlH4 doped with transition metal compounds. Despite a multitude of investigations of the effect of the added catalyst on the hydrogen sorption kinetics of NaAlH4, the mechanism of catalysis remains elusive so far. Following the decomposition of TiCl3-doped NaAlH4 by in-situ X-ray photoelectron spectroscopy (XPS), we link the chemical state of the dopant with those of the hydride and decomposition products. Titanium and aluminium change their oxidation states during cycling. The change of the formal oxidation state of Al from III to zero is partly due to the chemical reaction from NaAlH4 to Al. Furthermore, aluminium oxide is formed (Al2O3), which coexists with titanium oxide (Ti2O3). The interplay of metallic and oxidized Ti with the oxide skin might explain the effectiveness of Ti and similar dopants (Ce, Zr…).

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On the determination of atomic charge via ESCA including application to organometallics

Cited by 187 publications

References 38 publications

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

LiF Doping of C₆₀Studied with X-ray Photoemission Shake-Up Analysis

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

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On the determination of atomic charge via ESCA including application to organometallics

Cited by 187 publications

References 38 publications

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

LiF Doping of C60Studied with X-ray Photoemission Shake-Up Analysis

Reactivity enhancement of oxide skins in reversible Ti-doped NaAlH4

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LiF Doping of C₆₀Studied with X-ray Photoemission Shake-Up Analysis