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Now showing items 1 - 16 of 29006

  • Surface Morphology and Stress in Electrodeposited Copper Nanofilms

    O'Grady, M.   Lenihan, C.   Buckley, D. N.  

    In-situ stress measurements and in-situ AFM imaging were employed to study stress evolution during the electrodeposition of copper nanofilms from acidic copper sulphate electrolyte, at overpotentials of 125-200 mV and to compare the observed stress and morphology changes with theoretical predictions. As the films grew, tensile stress initially increased, corresponding to grain coalescence as observed by AFM, and reached a plateau value when significant GB volume had occurred. The time evolution of stress was examined during interruption of deposition. Generally, when deposition was interrupted, tensile stress decreased as predicted by Chason's model(13) for low mobility deposits. At all potentials, upon resuming deposition stress recovered to its pre-interrupted state. Stress increased with increasing overpotential as expected from theory. Cl -was found to directly reduce stress and resulted in a rougher surface than was observed without additives.
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  • A Study of the Photoelectrochemical Etching of n-GaN in H3PO4 and KOH Electrolytes

    Heffernan, C.   Lynch, R. P.   Buckley, D. N.  

    We investigated the photoelectrochemical etching of n-GaN in H3PO4 and KOH as a function of electrolyte concentration, potential and light intensity. Etch rates measured by stylus profilometry were compared with coulometric and amperometric values. In both electrolytes, etch rates increased with concentration, reaching a maximum at 3.0 mol dm(-3) and decreasing at higher concentrations. The increase in etch rate with concentration of either H3PO4 or KOH reflects the amphoteric nature of gallium and the decrease above 3.0 mol dm(-3) is attributed to common-ion effects. Profilometric etch rates were lower than coulometric and amperometric etch rates reflecting formation of a surface film. SEM and profilometry demonstrated that thick surface films are formed at lower concentrations. Etch rates increased linearly with light intensity indicating a carrier-limited etching regime: a quantum efficiency of 57.6% was obtained. At light intensities greater than similar to 35 mW cm(-2) the etch rates showed evidence of saturation. AFM and SEM images of the etched GaN surfaces showed a distinctive ridge-trench structure with a hexagonal appearance. Photoluminescence spectra of the etched GaN show a significant increase in the defect-related yellow luminescence peak suggesting correlation to the formation of the ridge structures, which may represent dislocations terminating at the surface. (C) The Author(s) 2019. Published by ECS.
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  • Propagation of Nanopores and Formation of Nanoporous Domains during Anodization of n-InP in KOH

    Buckley, D. N.   Lynch, R. P.   Quill, N.   O\"Dwyer, C.  

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  • Influence of Pretreatment on Kinetics at Carbon Electrodes and Consequences for Flow Battery Performance

    Buckley, D. N.   Bourke, A.   Lynch, R. P.   Quill, N.   Miller, M. A.   Wainright, J. S.   Savinell, R. F.  

    Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), it was shown for four different types of carbon that electrode treatments at negative potentials enhance the kinetics of V-IV-V-V and inhibit the kinetics of V-II-V-III while electrode treatments at positive potentials inhibit the kinetics of V-IV-V-V and enhance the kinetics of V-II-V-III. These observations may explain conflicting reports in the literature. The potentials required for activation and deactivation of electrodes were examined in detail. The results suggest that interchanging the positive and negative electrodes in a vanadium flow battery (VFB) would reduce the overpotential at the negative electrode and so improve the performance. This is supported by flow-cell experiments. Thus, periodic catholyte-anolyte interchange, or equivalent alternatives such as battery overdischarge, show promise of improving the voltage efficiency of VFBs.
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  • Influence of Pretreatment on Kinetics at Carbon Electrodes and Consequences for Flow Battery Performance

    Buckley, D. N.   Bourke, A.   Lynch, R. P.   Quill, N.   Miller, M. A.   Wainright, J. S.   Savinell, R. F.  

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  • Anodic formation and characterization of nanoporous InP in aqueous KOH electrolytes RID F-9784-2011

    O'Dwyer, C.   Buckley, D. N.   Sutton, D.   Newcomb, S. B.  

    The anodic behavior of highly doped (> 10(18) cm(-3)) n-InP in aqueous KOH was investigated. Electrodes anodized in the absence of light in 2-5 mol dm(-3) KOH at a constant potential of 0.5 - 0.75 V (SCE), or subjected to linear potential sweeps to potentials in this range, were shown to exhibit the formation of a nanoporous subsurface region. Both linear sweep voltammograms and current-time curves at constant potential showed a characteristic anodic peak, corresponding to formation of the nanoporous region. No porous region was formed during anodization in 1 mol dm(-3) KOH. The nanoporous region was examined using transmission electron microscopy and found to have a thickness of some 1 - 3 mu m depending on the anodization conditions and to be located beneath a thin (typically similar to 40 nm), dense, near-surface layer. The pores varied in width from 25 to 75 nm and both the pore width and porous region thickness were found to decrease with increasing KOH concentration. The porosity was approximately 35%. The porous layer structure is shown to form by the localized penetration of surface pits into the InP, and the dense, near-surface layer is consistent with the effect of electron depletion at the surface of the semiconductor. (c) 2006 The Electrochemical Society.
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    Buckley, D. N.   Forrest, J. B.  

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  • Growth of InGaAs structures using in situ electrochemically generated arsine

    Buckley, D. N.   Seabury, C. W.   Valdes, J. L.   Cadet, G.   Mitchell, J. W.   DiGiuseppe, M. A.   Smith, R. C.   Filipe, J. R. C.   Bylsma, R. B.   Chakrabarti, U. K.   Wang, K-W.  

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  • In-Situ AFM Imaging and Stress Measurements during Interruption of Electrochemical Deposition of Copper Nanofilms

    Buckley, D. N.   O'Grady, M.   Lenihan, C.  

    In-situ stress measurements and in-situ AFM imaging were employed to study time evolution of stress during interruption of the room-temperature electrodeposition of copper nanofilms. Generally, when deposition was interrupted, tensile stress decreased as predicted by Chason's model for low mobility deposits. At all potentials, upon resuming deposition stress recovered to its pre-interrupted state. The relative reduction in stress during interruption increased with increasing overpotential.
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  • Structural and Electrochemical Characterization of Thermally Treated Vanadium Oxide Nanotubes for Li-ion Batteries

    McNulty, D.   Buckley, D. N.   O'Dwyer, C.  

    Vanadium oxide nanotubes (VONTs) have been successfully synthesized by hydrothermal treatment of a mixture of vanadium oxide xerogel and nonylamine. Traditionally dodecylamine and hexadecylamine are used as the structure maintaining template. In this study, however, evidence of high quality nanotubes templated with nonylamine is presented. Thermogravimetric analysis was used to determine the temperature at which the amine molecules can be removed from the nanotubes. The removal of amines is desirable as heavy functionalization of VONTs by amine molecules can impede the intercalation of lithium ions. The removal of the amine chains resulted in a change in morphology from pristine nanotubes to polycrystalline vanadium oxide nanorods. High resolution transmission electron microscopy was used to characterize the VONTs before and after annealing to high temperatures. Fourier transform infrared spectroscopy confirmed the removal of the amine template after annealing. Galvanostatic discharge tests were performed to compare the electrochemical behavior of bulk V2O5 powder, VONTs and polycrystalline nanorods (poly-NRs). A comparison of their specific capacity values after the first discharge is also presented.
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  • Towards Optical Monitoring of Vanadium Redox Flow Batteries (VRFBs): An Investigation of the Underlying Spectroscopy

    Buckley, D. N.   Gao, X.   Lynch, R. P.   Quill, N.   Leahy, M. J.  

    The UV-visible spectra of V III-V II electrolytes in 3 mol dm -3 H 2SO 4 showed a linear relationship of absorbance to mole fraction but those of V IV-V V electrolytes did not. At all wavelengths, V IV-V V mixtures showed excess absorbance over that expected for a linear combination of the components. Plots of excess absorbance A ex against mole fraction f of V IV were found to be symmetrical parabolas that reach a peak at a mole fraction f = 0.5. Excess absorbance is attributed to a strongly absorbing 1:1 mixed-valence complex, V 2O 33+, in equilibrium with VO 2+ and VO 2+. Based on this, an expression is derived that relates A ex to f and from this it is shown that when K cC < 1 (where K c is the equilibrium constant and C is the total vanadium concentration), A ex should vary linearly with f(1 - f). Experimentally, plots of A ex versus f(1 - f) showed excellent linearity through the origin at all wavelengths, thus confirming the model. An excess molar extinction coefficient epsilon ex and an alternative excess absorbance parameter p are defined. Values of p and approximate values of K c and epsilon ex were estimated; the spectrum of V 2O 33+ is plotted as its approximate molar extinction coefficient.
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  • An investigation by AFM and TEM of the mechanism of anodic formation of nanoporosity in n-InP in KOH RID F-9784-2011

    O'Dwyer, C.   Buckley, D. N.   Sutton, D.   Serantoni, M.   Newcomb, S. B.  

    The early stages of nanoporous layer formation, under anodic conditions in the absence of light, were investigated for n-type InP with a carrier concentration of similar to 3 x 10(18) cm(-3) in 5 mol dm(-3) KOH and a mechanism for the process is proposed. At potentials less than similar to 0.35 V, spectroscopic ellipsometry and transmission electron microscopy (TEM) showed a thin oxide film on the surface. Atomic force microscopy (AFM) of electrode surfaces showed no pitting below similar to 0.35 V but clearly showed etch pit formation in the range 0.4-0.53 V. The density of surface pits increased with time in both linear potential sweep and constant potential reaching a constant value at a time corresponding approximately to the current peak in linear sweep voltammograms and current-time curves at constant potential. TEM clearly showed individual nanoporous domains separated from the surface by a dense similar to 40 nm InP layer. It is concluded that each domain develops as a result of directionally preferential pore propagation from an individual surface pit which forms a channel through this near-surface layer. As they grow larger, domains meet, and the merging of multiple domains eventually leads to a continuous nanoporous sub-surface region. (c) 2006 The Electrochemical Society. [DOI: 10.1149/1.2401029] All rights reserved.
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  • (Keynote) In Situ AFM Imaging and Stress Measurements during Interruption of Electrochemical Deposition of Copper Nanofilms

    Buckley, D. N.   O\"Grady, M.   Lenihan, C.  

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    Nakahara, S.   Ahmed, S.   Buckley, D. N.  

    During room-temperature aging, a morphological transition described as a spontaneous morphology change was discovered to occur on the surface of single-crystal copper electrodeposits grown epitaxially on {001} copper substrates. Within half to two hours after the completion of deposition, well-defined periodic contour lines appeared suddenly around the originally smooth-faced pyramids. These contour lines were thought to represent periodic cracks/steps, which were formed to relieve tensile stress developed as a result of surface annihilations of excess vacancies trapped in the deposits. Thus the formation of these lines was phenomenologically the same as the sudden appearance of fine grains observed previously on the surface of polycrystalline copper electrodeposits during room-temperature aging.
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  • (n,d)-Injective covers,n-coherent rings, and (n,d)-rings

    Li, Weiqing   Ouyang, Baiyu  

    It is known that a ring R is left Noetherian if and only if every left R-module has an injective (pre)cover. We show that (1) if R is a right n-coherent ring, then every right R-module has an (n, d)-injective (pre)cover; (2) if R is a ring such that every (n, 0)-injective right R-module is n-pure extending, and if every right R-module has an (n, 0)-injective cover, then R is right n-coherent. As applications of these results, we give some characterizations of (n, d)-rings, von Neumann regular rings and semisimple rings.
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  • Triples which are D ( n )-sets for several n \"s

    Ad?aga, Nikola   Dujella, Andrej   Kreso, Dijana   Tadi?, Petra  

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