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Leo W. M. Lau

Bio: Leo W. M. Lau is an academic researcher from University of Western Ontario. The author has contributed to research in topics: Chemical state & Silane. The author has an hindex of 7, co-authored 8 publications receiving 6806 citations.
Topics: Chemical state, Silane, Molecule, Nickel, Hydrogen

Papers
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Journal ArticleDOI
TL;DR: Biesinger et al. as mentioned in this paper proposed a more consistent and effective approach to curve fitting based on a combination of standard spectra from quality reference samples, a survey of appropriate literature databases and/or a compilation of literature references and specific literature references where fitting procedures are available.

7,498 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: Auger parameter analysis indicates that the bonding in NiO appears to have stronger contributions from initial state charge transfer from the oxygen ligands than that in the hydroxide and oxyhydroxide consistent with the considerable differences in the Ni-O bond lengths in these compounds with some relaxation of this state occurring during final state phenomena.
Abstract: The critical role of the Auger parameter in providing insight into both initial state and final state factors affecting measured XPS binding energies is illustrated by analysis of Ni 2p3/2 and L3M45M45 peaks as well as the Auger parameters of nickel alloys, halides, oxide, hydroxide and oxy-hydroxide. Analyses of the metal and alloys are consistent with other works, showing that final state relaxation shifts, ΔR, are determined predominantly by changes in the d electron population and are insensitive to inter-atomic charge transfer. The nickel halide Auger parameters are dominated by initial state effects, Δe, with increasing positive charge on the core nickel ion induced by increasing electronegativity of the ligands. This effect is much greater than the final state shifts; however, the degree of covalency is reflected in the Wagner plot where the more polarizable iodide and bromide have greater ΔR. The initial state shift for NiO is much smaller than those of Ni(OH)2 or NiOOH and the effective oxidation state is much less than that inferred from the average electronegativity of the ligand(s). Auger parameter analysis indicates that the bonding in NiO appears to have stronger contributions from initial state charge transfer from the oxygen ligands than that in the hydroxide and oxyhydroxide consistent with the considerable differences in the Ni–O bond lengths in these compounds with some relaxation of this state occurring during final state phenomena. The Auger parameter of NiOOH is, however, shifted positively, like the iodide, indicating greater polarizability of the ligands and covalency in this bonding. There is support for more direct use of relative bond lengths in interpreting differences between related compounds rather than more general electronegativity or similar parameters.

272 citations

Patent
03 Mar 2010
TL;DR: In this article, the authors present a method for growing multilayer polymer based heterojunction devices which uses selective breaking of C-H or Si-H bonds without breaking other bonds leading to fast curing for the production of layered polymer devices.
Abstract: Method for growing multilayer polymer based heterojunction devices which uses selective breaking of C—H or Si—H bonds without breaking other bonds leading to fast curing for the production of layered polymer devices having polymer heterojunctions deposited by the common solution-based deposition methods In one embodiment, a hydrogen plasma is maintained and protons are extracted with an electric field to accelerate them to an appropriate kinetic energy The protons enter into a drift zone to collide with molecular hydrogen in gas phase The cascades of collisions produce a high flux of hyperthermal molecular hydrogen with a flux many times of the flux of protons extracted from the hydrogen plasma The nominal flux ratio of hyperthermal molecular hydrogen to proton is easily controllable by the hydrogen pressure in the drift zone, and by the length of the drift zone The extraction energy of the protons is shared by these hyperthermal molecules so that average energy of the hyperthermal molecular hydrogen is easily controlled by extraction energy of the protons and the nominal flux ratio Since unlike protons the hyperthermal molecular hydrogen projectiles do not carry any electrical charge, the high flux of hyperthermal molecular hydrogen can be used to engineer surface modification of both electrical insulating products and conductive products In a typical embodiment, organic precursor molecules (or silicone, or silane molecules) with desirable chemical functionality or a set of functionalities and with desirable electrical properties are condensed on a substrate with a solution-based deposition method The molecular layer is bombarded by the high flux of hyperthermal molecular hydrogen derived from a hydrogen plasma The C—H or Si—H bonds are thus cleaved preferentially due to the kinematic selectivity of energy deposition from the hyperthermal hydrogen projectiles to the hydrogen atoms in the precursor molecules The induced cross-linking reactions produce a stable molecular layer retaining the desirable chemical functionality/functionalities and electrical properties carried to the substrate by the precursor molecules The molecular layer is thus cured and ready for additional molecular layer formation for the production of polymer devices which typically comprise one or more than one polymer heterojunction

17 citations

Journal ArticleDOI
TL;DR: A Micro‐delivery approach for Studying Microvascular Responses to Localized Oxygen Delivery and its applications in medicine and materials science is proposed.
Abstract: In vivo video microscopy has been used to study blood flow regulation as a function of varying oxygen concentration in microcirculatory networks. However, previous studies have measured the collective response of stimulating large areas of the microvascular network at the tissue surface. Objective We aim to limit the area being stimulated by controlling oxygen availability to highly localized regions of the microvascular bed within intact muscle.

17 citations


Cited by
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Journal ArticleDOI
TL;DR: Biesinger et al. as mentioned in this paper proposed a more consistent and effective approach to curve fitting based on a combination of standard spectra from quality reference samples, a survey of appropriate literature databases and/or a compilation of literature references and specific literature references where fitting procedures are available.

7,498 citations

Journal ArticleDOI
TL;DR: In this article, a vanadium oxide bronze was used as the positive electrode for a Zn cell with reversible intercalation of Zn ions in a layered Zn0.25V2O5⋅nH2O-based positive electrode.
Abstract: Although non-aqueous Li-ion batteries possess significantly higher energy density than their aqueous counterparts, the latter can be more feasible for grid-scale applications when cost, safety and cycle life are taken into consideration. Moreover, aqueous Zn-ion batteries have an energy storage advantage over alkali-based batteries as they can employ Zn metal as the negative electrode, dramatically increasing energy density. However, their development is plagued by a limited choice of positive electrodes, which often show poor rate capability and inadequate cycle life. Here we report a vanadium oxide bronze pillared by interlayer Zn2+ ions and water (Zn0.25V2O5⋅nH2O), as the positive electrode for a Zn cell. A reversible Zn2+ ion (de)intercalation storage process at fast rates, with more than one Zn2+ per formula unit (a capacity up to 300 mAh g−1), is characterized. The Zn cell offers an energy density of ∼450 Wh l−1 and exhibits a capacity retention of more than 80% over 1,000 cycles, with no dendrite formation at the Zn electrode. High-performing positive electrode materials are crucial for the development of aqueous Zn-ion batteries. Here the authors report a battery based on reversible intercalation of Zn ions in a layered Zn0.25V2O5⋅nH2O-based positive electrode, which exhibits high-capacity and long-term cycling stability.

1,948 citations

Journal ArticleDOI
TL;DR: In this article, the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions is discussed, with an outlook on the opportunities in future research within this rapidly developing field.
Abstract: In this Review, we discuss the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions. Understanding and mastering the kinetics of oxygen electrocatalysis is instrumental to making use of photosynthesis, advancing solar fuels, fuel cells, electrolyzers, and metal–air batteries. We first present key insights, assumptions and limitations of well-known activity descriptors and reaction mechanisms in the past four decades. The turnover frequency of crystalline oxides as promising catalysts is also put into perspective with amorphous oxides and photosystem II. Particular attention is paid to electronic structure parameters that can potentially govern the adsorbate binding strength and thus provide simple rationales and design principles to predict new catalyst chemistries with enhanced activity. We share new perspective synthesizing mechanism and electronic descriptors developed from both molecular orbital and solid state band structure principles. We conclude with an outlook on the opportunities in future research within this rapidly developing field.

1,503 citations

Journal ArticleDOI
TL;DR: It is hypothesized that Fe is the most-active site in the catalyst, while CoOOH primarily provides a conductive, high-surface area, chemically stabilizing host.
Abstract: Cobalt oxides and (oxy)hydroxides have been widely studied as electrocatalysts for the oxygen evolution reaction (OER). For related Ni-based materials, the addition of Fe dramatically enhances OER activity. The role of Fe in Co-based materials is not well-documented. We show that the intrinsic OER activity of Co1–xFex(OOH) is ∼100-fold higher for x ≈ 0.6–0.7 than for x = 0 on a per-metal turnover frequency basis. Fe-free CoOOH absorbs Fe from electrolyte impurities if the electrolyte is not rigorously purified. Fe incorporation and increased activity correlate with an anodic shift in the nominally Co2+/3+ redox wave, indicating strong electronic interactions between the two elements and likely substitutional doping of Fe for Co. In situ electrical measurements show that Co1–xFex(OOH) is conductive under OER conditions (∼0.7–4 mS cm–1 at ∼300 mV overpotential), but that FeOOH is an insulator with measurable conductivity (2.2 × 10–2 mS cm–1) only at high overpotentials >400 mV. The apparent OER activity of ...

1,449 citations

Journal ArticleDOI
TL;DR: The high OER activity and simple synthesis make these Ni-based catalyst thin films useful for incorporating with semiconductor photoelectrodes for direct solar-driven water splitting or in high-surface-area electrodes for water electrolysis.
Abstract: Water oxidation is a critical step in water splitting to make hydrogen fuel. We report the solution synthesis, structural/compositional characterization, and oxygen evolution reaction (OER) electrocatalytic properties of ∼2–3 nm thick films of NiOx, CoOx, NiyCo1–yOx, Ni0.9Fe0.1Ox, IrOx, MnOx, and FeOx. The thin-film geometry enables the use of quartz crystal microgravimetry, voltammetry, and steady-state Tafel measurements to study the electrocatalytic activity and electrochemical properties of the oxides. Ni0.9Fe0.1Ox was found to be the most active water oxidation catalyst in basic media, passing 10 mA cm–2 at an overpotential of 336 mV with a Tafel slope of 30 mV dec–1 with oxygen evolution reaction (OER) activity roughly an order of magnitude higher than IrOx control films and similar to the best known OER catalysts in basic media. The high activity is attributed to the in situ formation of layered Ni0.9Fe0.1OOH oxyhydroxide species with nearly every Ni atom electrochemically active. In contrast to pr...

1,306 citations