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Nitrogen-doped films of ZnO grown by two methods, metalorganic chemical vapor deposition (MOCVD) and reactive sputtering, were studied with x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). Systematic differences in the N chemical states were observed between films grown by sputtering and MOCVD: only two N chemical states were observed in films grown by reactive sputtering, whereas four N chemical states were observed in MOCVD films. To aid in the assignment of the N chemical states, photoemission data from the polycrystalline films were compared with data taken on N2+-implanted Zn metal and N2+-implanted ZnO. High-resolution core level spectra of the N 1s region indicated that nitrogen can occupy at least four different chemical environments in ZnO; these include the NO acceptor, the double donor (N2)O, and two carbon–nitrogen species. Valence band spectra indicate that the Fermi energy of all films studied was near the conduction band minimum, implying that the films remained n-type after nitrogen doping. Analysis of the relative amounts of acceptors and donors identified by XPS in the sputter-grown films provides clues as to why only a small percentage of incorporated nitrogen is found to contribute to carriers, and points toward possible paths to higher quality ZnO:N films. [ABSTRACT FROM AUTHOR]

Microstructural changes of amorphous V[sub 2]O[sub 5] films with lithium intercalation are studied using Raman-scattering measurements. The Raman spectra of as-deposited films show two broad peaks around at 520 and 650 cm[sup -1], due to the stretching modes of the [sub V]3-O and V[sub 2]-O bonds, respectively, and a relatively sharp peak at 1027 cm[sup -1] due to the V[sup 5+]=O stretching mode of terminal oxygen atoms. In addition, there is a peak at 932 cm[sup -1] that we attribute to the V[sup 4+]=O bonds. Comparison of the Raman spectra of V[sub 2]O[sub 5] films with different oxygen deficiencies confirms this assignment. This Raman peak due to the stretching mode of the V[sup 4+]=O bonds develops and shifts toward lower frequencies with increasing lithium concentration. Comparison to results from gasochromic hydrogen insertion indicates that the 932 cm[sup -1] Raman peak is not a result of vibrations which involve Li or H atoms. We propose that the V[sup 4+]=O bonds are created by two different mechanisms: a direct conversion from V[sup 5+] = O bonds and the breaking of the single oxygen bonds involving V[sup 4+] ions. [ABSTRACT FROM AUTHOR]

In this work, a combination of constituent materials capable of improving the moisture retention and proton conductivity (PC) was incorporated into sulfonated poly (ether ether ketone) (SPEEK) membranes in order to prepare new, self-humidifying composite membranes (SHMs) for proton exchange membrane fuel cells. The property-improving components were incorporated into the cast SPEEK film in an appropriate microstructural architecture to prepare the SHMs with increased water retention and PC. SHMs were therefore prepared with the inclusion of carboxyl-functionalized graphene (G(c)) and phosphotungstic acid (PWA) with varying proportions into the SPEEK film. The structure of the SPEEK/G(c)/PWA composite membranes was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The physicochemical properties of the composite membranes, such as ion exchange capacity, water uptake, thermal stability and PC, were investigated. This work provides confirmation that self-humidifying properties are improved at temperature above 60 °C through a combinational inclusion of G(c) and PWA within SPEEK and the new self-humidifying membranes have potential for use in medium temperature direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

The performance of Al2O3 atomic layer deposition (ALD) coatings for LiCoO2/natural graphite (LCO/NG) batteries is investigated, where various permutations of the electrodes are coated in a full battery. Coating both electrodes with ∼1 nm of alumina as well as coating only the LCO (positive electrode) enables improved performance when cycling at high voltage, where the LCO is known to degrade. However, we found that coating only the NG (negative electrode) also improves the performance of the whole battery when cycling at high voltage. Under these conditions, the uncoated LCO (positive electrode) should degrade quickly, and the NG should be unaffected. A variety of characterization techniques show the surface reactions that occur on the negative electrode and positive electrode are related, resulting in the enhanced performance of the uncoated LCO. [ABSTRACT FROM AUTHOR]

Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO2 cathode powders coated with metal oxides with thicknesses of ∼100 to 1000 Å grown using wet chemical techniques improved LIB performance. In this study, LiCoO2 powders were coated with conformal Al2O3 ALD films with thicknesses of only ∼ 3 to 4 A established using two ALD cycles. The coated LiCoO2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V (vs Li/LiF) range. In contrast, the bare LiCoO2 powders displayed only a 45% capacity retention. Al2O3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin A12O3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance. [ABSTRACT FROM AUTHOR]

Abstract: Electrochromic (EC) properties of sputtered Ni oxide films have been examined in 1M KCl+H2SO4 acidic aqueous solutions with H2SO4 concentrations of 0–50mM. EC coloration efficiency comparable to that in alkaline electrolytes was obtained in all the solutions and no remarkable degradation in charge capacity was observed up to 100 cycles. These results offer support for the practical construction of efficient complementary EC devices using dilute acidic aqueous electrolytes. [Copyright &y& Elsevier]

We report on the electrochromic behavior of amorphous ruthenium oxide thin films and their electrochemical characteristics for use as counterelectrodes for electrochromic devices. Hydrous ruthenium oxide thin films were prepared by cyclic voltammetry on ITO coated glass substrates from an aqueous ruthenium chloride solution. The cyclic voltammograms of this material show the capacitive behavior including two redox reaction peaks in each cathodic and anodic scan. The ruthenium oxide thin film electrode exhibits a 50% modulation of optical transmittance at 670 nm wavelength with capacitor charge/discharge. [Copyright &y& Elsevier]

Electrochromic (EC) devices fabricated with liquid or polymeric gel electrolyte are often less durable than those constructed with inorganic solid-state electrolyte. Long-term degradation of the ion insertion layer (with extensive cycling) by the liquid/gel electrolyte may contribute to this durability problem. In this respect, two V2O5 thin film electrodes were fabricated for extensive cyclic durability testing in a LiClO4/propylene carbonate (PC) liquid electrolyte: One V2O5 film had no overlying coating while the other had a protective thin film of solid lithium ion-conducting LiAlF4. The protected V2O5 exhibited improved durability in terms of constant capacity with repeated cycling up to 800 cycles, while the uncoated V2O5 electrode displayed significant capacity loss. Our results demonstrate that deposition of an inorganic solid electrolyte (LiAlF4) on amorphous V2O5 films serves as a protective overlayer and enhances the long-term cycling efficiency and stability of the V2O5 in a liquid electrolyte. [Copyright &y& Elsevier]

We report on the microstructural changes of amorphous V2O5 films with lithium intercalation. The Raman spectra of as-deposited films show two broad peaks around at 520 and 650 cm−1, due to the stretching modes of the V3–O and V2–O bonds, respectively, and a relatively sharp peak at 1027 cm−1 due to the V5+&z.dbnd6;O stretching mode of terminal oxygen atoms. In addition, there is a peak at 932 cm−1 that we attribute to the V4+&z.dbnd6;O bonds. Comparison of the Raman spectra of V2O5 films with different oxygen deficiencies confirms this assignment. This Raman peak due to the stretching mode of the V4+&z.dbnd6;O bonds develops and shifts toward lower frequencies with increasing lithium concentration. Comparison to results from gasochromic hydrogen insertion indicates that the 932 cm−1 Raman peak is not a result of vibrations which involve Li or H atoms. We propose that the V4+&z.dbnd6;O bonds are created by two different mechanisms: a direct conversion from V5+&z.dbnd6;O bonds and the breaking of the single oxygen bonds involving V4+ ions. [Copyright &y& Elsevier]

A detailed systematic study of the tungsten oxide thin films has been carried out using WO3 films after they were annealed at progressively increasing temperatures ranging from 350°C to 450°C in oxygen environments. The structural properties of the films were characterized using X-ray diffraction and Raman spectroscopy. The amorphous WO3 films remain as an amorphous phase up to 385°C and begin to crystallize at 390°C and then are completely crystallized at 450°C. Absorption peaks of the films are found to shift to a higher energy side with increasing annealing temperature up to 385°C and then shift abruptly to a lower energy as the films begin to crystallize at 390°C. Deconvolution of the absorption spectra shows that there are two different polaron transitions in the amorphous WO3 films. [Copyright &y& Elsevier]

Vanadium oxide prepared by plasma-enhanced chemical vapor deposition was cycled in different voltage ranges in a lithium battery. Electrochemical cycling results show a surprisingly low irreversibility during the first discharge and good stability for close to 1000 cycles between 4 and 0 V. Raman spectroscopy results indicate that a major structural transformation takes place when the films are cycled down to 1.8 V, after which the structural features remain intact even after cycling to 0 V. Degradation of the electrode only occurs after extended cycling. [Copyright &y& Elsevier]

Intercalation of lithium ions in amorphous tungsten oxide films and in monoclinic polycrystalline tungsten oxide films has been studied using electrochemical analyses and Raman spectroscopy. We present direct evidence for W5+ 5d-electron localization in amorphous tungsten oxide films upon lithium ion and electron intercalation by comparing the Raman spectra of amorphous and crystalline tungsten oxide films. We observe that when lithium ions and electrons are inserted into the crystalline tungsten oxide films, the monoclinic structure of the material proceeds to progressively increased symmetry. On the other hand, when lithium ions and electrons are inserted into amorphous tungsten oxide films, the inserted electrons are localized in W5+ sites and polarize their surrounding lattice to form small polarons. The extra Raman peaks due to the W5+&z.sbnd;O single bonds and W5+&z.dbnd6;O double bonds appear at 330 and 450 cm−1, respectively. [Copyright &y& Elsevier]

Standard and mesoporous sol–gel tungsten oxide thin films were prepared by a spin-coating technique from an ethanolic solution of tungsten hexachloride. A block copolymer (BASF™ Pluronic p123) was employed as a template to generate the mesoporous structure. An ultraviolet (UV) illumination method was employed to remove the polymer templates at room temperature. The electrochromic and optical properties of the mesoporous films are described and compared to standard sol–gel tungsten oxide films. Results are also presented on the samples prepared by thermal treatment. We demonstrate that the UV illumination/ozone treatment is a superior method to remove templates which enables us to more effectively investigate the effect of mesoporosity on the electrokinetics of ion insertion into tungsten oxide films. [Copyright &y& Elsevier]

Reports on the preparation of mesostructured vanadium oxides and the vanadophosphate system using the electrodeposition process. Recognition of the system's advantage in initiating an oxidation reaction without chemical agents, having reaction rate control and direct formation of the product material in a thin film form; Application of the synthesis technique to the deposit of mesostructured vanadium oxide and vanadophosphate in the presence of ionic surfactants; Inclusion of the infrared spectra measurements in the material's inorganic framework characterization.

The chemical diffusion of lithium ions in a-Li[sub x]WO[sub 3] films is investigated using alternating current impedance spectroscopy and Raman scattering measurements. The diffusion coefficients increase with increasing x in a-Li[sub x]WO[sub 3] up to x=0.072 and then decrease. Raman measurements show that the W[sup 6+]=O/O-W[sup 6+]-O ratio also increases at the early stage of lithium insertion and then decreases with further lithium insertion. We conclude that the diffusion kinetics of lithium ions in a-Li[sub x]WO[sub 3] films is very closely related to the W[sup 6+]=O/O-W[sup 6+]-O ratio. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of amorphous V2O5 thin films with various organic vapors is investigated using in-situ optical transmission and in-situ Raman spectroscopic measurements. When V2O5 thin films are exposed to vapors of methanol, ethanol, acetone, and isopropanol, changes in the Raman spectrum are observed. These changes are similar to those due to alkali ion intercalation and most pronounced for methanol and ethanol. The optical transmission also increases when the thin films are exposed to methanol and ethanol vapors. Depositing a thin catalyst layer of palladium does not promote the reaction. This result has implications for using this material in hydrogen sensor applications, as extended exposure to organic vapors may not be differentiated from the presence of hydrogen. [Copyright &y& Elsevier]

Abstract: We have used Pd–Pt alloy as the catalyst in the hydrogen sensor thin film. Palladium and platinum were co-sputtered on top of a tungsten oxide layer grown by reactive sputtering. Both the sensitivity and the durability were dramatically improved over the case of a palladium single-component catalyst. The fractional change in the optical absorption on exposure to 1% hydrogen gas was increased by a factor larger than 2, and the fractional change decreased only a little after more than 1000 cycles of repeated exposure to 1% hydrogen and air. Moreover, the sensor film exhibited good selectivity to other organic vapors. [Copyright &y& Elsevier]

Abstract: Crystalline WO3 nanoparticles are employed in the development of flexible electrochromic (EC) devices. The nanoparticles are synthesized at high-density with a hot-wire chemical vapor deposition process where the hot filament provides the source of the tungsten metal. Polyethylene terephthalate coated with indium tin oxide is employed as a transparent flexible substrate. A simple electrophoresis technique is employed to deposit the WO3 nanoparticles on the polymer, resulting in a uniform thin film. The EC performance is optimized for WO3 particles that were baked at ~300 °C for 2 h prior to electrode fabrication. The transmittance is modulated between ~94% and ~28% without degradation for 100 cycles. [Copyright &y& Elsevier]