Electrochromic nickel oxide films made by reactive r.f. sputtering from different targets

We describe the preparation and optical–electrical characterization of thin electrochromic layers based on nickel oxide (NiO_x). These layers were deposited by reactive radiofrequency (r.f.) sputtering from nickel or nickel oxide targets, maintaining the r.f. power and varying the oxygen flow in a gas mixture of Ar and O₂ from 5% up to 30%. The Ni/O ratio in the deposited thin films was determined by Rutherford backscattering spectroscopy (RBS) and the microstructure was investigated by x‐ray diffraction. The deposition rate was found to be strongly dependent on the type of target used. The electrochromic behaviour in aqueous alkaline electrolyte (0.1 N KOH solution) was investigated by electrochemical cyclization. Samples deposited by the NiO target exhibited the lowest N/O ratio (0.5) and the highest value of intercalated charge (～4.9 × 10^?2 mC cm^?2 nm^?1). Among the same samples the highest value of the intercalated charge was found for those deposited at low oxygen flow, but these samples exhibit the smallest reversible changes in optical absorption in the wavelength range 330–1200 nm. Samples deposited by the nickel target do not exhibit significant variations in the value of the exchanged charge; the measured Ni/O ratio indicates a stoichiometry closer to NiO. We also observed the switching behaviour by analysing the films in cyclic time mode at a fixed wavelength. The commutation response time is estimated by measurement under the application of a step waveform potential. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of Cu-Modified Nickel Oxide Nanocrystals and Their Applications as Hole-Injection layers for Quantum-Dot Light-Emitting Diodes

Solution-processed NiO_x thin films have been applied as hole-injection layers (HILs) in quantum-dot light-emitting diodes (QLEDs). The commonly used NiO_x HILs are prepared by the precursor-based route, which requires high annealing temperatures of over 275 °C to in situ convert the precursors into oxide films. Such high processing temperatures of NiO_x HILs hinder their applications in flexible devices. Herein, we report a low-temperature approach based on Cu-modified NiO_x (NiO_x-Cu) nanocrystals to prepare HILs. A simple post-synthetic surface-modification step, which anchors the copper agents onto the surfaces of oxide nanocrystals, is developed to improve the electrical conductivity of the low-temperature-processed (135 °C) oxide-nanocrystal thin films. In consequence, QLEDs based on the NiO_x-Cu HILs exhibit an external quantum efficiency of 17.5 % and a T₉₅ operational lifetime of ∼2,800 h at an initial brightness of 1,000 cd m⁻², meeting the commercialization requirements for display applications. The results shed light on the potential of using NiO_x-Cu HILs for realizing high-performance flexible QLEDs.     

Formation of NiO/YSZ functional anode layers of solid oxide fuel cells by magnetron sputtering

The decrease in the polarization resistance of the anode of solid-oxide fuel cells (SOFCs) due to the formation of an additional NiO/(ZrO₂ + 10 mol % Y₂O₃) (YSZ) functional layer was studied. NiO/YSZ films with different NiO contents were deposited by reactive magnetron sputtering of Ni and Zr–Y targets. The elemental and phase composition of the films was adjusted by regulating oxygen flow rate during the sputtering. The resulting films were studied by scanning electron microscopy and X-ray diffractometry. Comparative tests of planar SOFCs with a NiO/YSZ anode support, NiO/YSZ functional nanostructured anode layer, YSZ electrolyte, and La_0.6Sr_0.4Co_0.2Fe_0.8O₃/Ce_0.9Gd_0.1O₂ (LSCF/CGO) cathode were performed. It was shown that the formation of a NiO/YSZ functional nanostructured anode leads to a 15–25% increase in the maximum power density of fuel cells in the working temperature range 500–800°C. The NiO/YSZ nanostructured anode layers lead not only to a reduction of the polarization resistance of the anode, but also to the formation of denser electrolyte films during subsequent magnetron sputtering of electrolyte.     

Electrochemical codeposition of nickel oxide and polyaniline

Nickel oxide (NiO_x) and polyaniline (PAni) were electrocodeposited from NiSO₄ and aniline through cyclic voltammetric scans to afford PAni–NiO_x composite film at controlled pH environment. The electrochemical activities of the film were investigated by cyclic voltammetry in 0.1 M NaOH and 0.1 M H₂SO₄, respectively. Typical redox couples of PAni in 0.1 M H₂SO₄ appeared at approximately 0.2 and 0.4 V vs. saturated calomel electrode (SCE); Ni(II)/Ni(III) redox couple was observed at approximately 0.4 V vs. SCE in 0.1 M NaOH. The morphologies and elemental components of the films were inspected by scanning electron microscopy and energy dispersive X-ray diffraction. The stability of nickel oxide in the films was found to be enhanced against acidic environments. Electrochemical catalytic behavior of NiO_x within the composite film was conserved and demonstrated by catalytic oxidation of methanol and ethanol.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

X-ray and UV photoemission studies of valence electronic structure of NiO

The X-ray and UV photoemission valence band spectra of NiO are interpreted using the molecular orbital theory for the NiO^10?₆ cluster and the sudden approximation (monopole selection rules). They exhibit the effects of crystal field splitting, multiplet splitting, electron shake-up (O 2pe^b_g→ Ni 3de^a_g). relaxation and Ni 3dO 2p hybridization. Shake-up satellite data indicate that the NiO optical absorption edge near 4 eV is associated with an O 2p → Ni 3d transition. The NiO valence electronic structure obtained in this work is compared with band structure models of Wilson and Mattheiss.     

Compatibility evaluation between La2Mo2O9 fast oxide-ion conductor and Ni-based materials

The chemical reactivity of La₂NiO_4+δ and nickel metal or nickel oxide with fast oxide-ion conductor La₂Mo₂O₉ is investigated in the annealing temperature range between 600 and 1000 °C, using room temperature X-ray powder diffraction. Within the La₂NiO_4+δ/La₂Mo₂O₉ system, subsequent reaction is evidenced at relatively low annealing temperature (600 °C), with formation of La₂MoO₆ and NiO. The reaction is complete at 1000 °C. At reverse, no reaction occurs between Ni or NiO and La₂Mo₂O₉ up to 1000 °C. Together with a previous work [G. Corbel, S. Mestiri, P. Lacorre, Solid State Sci. 7 (2005) 1216], the current study shows that Ni-CGO cermets might be chemically and mechanically compatible anode materials to work with LAMOX electrolytes in solid oxide fuel cells.     

HfNixP – Intercalation of Ni into the Three-Dimensional Compound HfP

The new compound HfNi_xP (x = 0.426(1), crystal structure: P6₃/mmc, a = 3.737(1) Å, c = 12.666(2) Å, V = 153.21(7) ų) has been prepared by arc-melting of HfP with nickel and subsequent annealing at 1400°C. Its crystal structure can be considered as a filled HfP structure, with the Ni atoms inserted into the trigonal prismatic voids of the Hf sublattice. Since the neighboring trigonal Hf₆ prisms are centered by P atoms, each of the three rectangular faces of the Hf₆Ni prism is capped with one P atom. Altogether, the structure of HfNi_xP consists of alternating layers of Hf atoms with the packing sequence AABB . One P and the Ni position are situated between the eclipsed Hf layers, whereas the other P site between the A and B layers is surrounded by six Hf atoms in a staggered arrangement. The calculated density of states (Extended Hückel approximation) points to metallic conductivity; threedimensional metallic behavior is assumed because of the Hf–Hf bonding interactions along all three directions.     

Magnetische Messungen in den Systemen (Zr,Hf)—(Fe,Co,Ni)—O

The phases Zr₃Fe, Zr₃CoO _x (x=0,35;1);Zr₃NiO _x (x=0,2; 1); Hf₃NiO are measured magnetically in the range between 1300°K and 90°K. Whereas Zr₃Fe is ferromagnetic, the other isotypical structures are paramagnetic.

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Nickel Oxidation State and Magnetic Properties of Hole-Doped and Reduced Nd2−xSrxNiOyCompounds

The NiK-edge XANES of reduced Nd_2−xSr_xNiO₄samples shows an increase of Ni³⁺content with Sr³⁺concentration. The appearance of mixed valence Ni²⁺/Ni³⁺produces a change in the magnetic properties of the system. The Nd³⁺sublattice orders antiferromagnetically atT_N∼13–20 K forx=0.4, 0.5, and 0.6, due to the interactions of Ni–Nd sublattices. Forx=0.8 this order begins to disappear because of the effect of the low spin state Ni³⁺created at the NiO₄planes. Additionally, the reduced family Nd_2−xSr_xNiO_y(y<4) shows the disappearance of Ni³⁺, the decrease of Ni²⁺with respect to the nonreduced form, and the appearance of Ni⁺. All the compounds of the reduced family show AF order at low temperature.     

Chloride‐Induced Highly Active Au Catalyst for Methyl Esterification of Alcohols

Chloride is generally regarded as a harmful species for the heterogeneous catalysts, especially Au catalysts. In this work, a series of active Au/NiO_x catalysts were successfully prepared with co‐precipitation method by tracking the concentrations of chloride in the re‐dispersed aqueous solutions. For methyl esterification of alcohols, the highest active Au/NiO_x catalysts could be prepared from aqueous solutions containing 8‐13 ppm chloride, the yield of methyl benzoate of catalyst Au/NiO_x‐9 was 99%. The catalyst structures and the role of chloride in catalysts were explored by ICP, BET, XPS, TEM and EXAFS characterizations. It was found that the appropriate amount of residual chloride in Au catalysts was beneficial to their catalytic activities. Especially for Au/NiO_x‐9, the appropriate amount of residual chloride had positive effects on the physicochemical properties of Au/NiO_x catalyst, the position of Au nanoparticles (NPs) located on NiO_x crystallites and the ratio of Au^δ+/Au⁰ in catalyst, which together resulted in its high reactivity.     

Über den aufgefüllten Re3B-Typ in den Systemen (Zr,Hf)−(Fe,Co, Ni)−O

Zusammenfassung Es wird gezeigt, daß die Oktaederlücken des Re₃B-Typs in obigen Systemen teilweise durch Sauerstoff aufgefüllt werden. Die Auffüllungsbereichex der Phasen Zr₃CoO _x , Zr₃NiO _x , Hf₃CoO _x und Hf₃NiO _x werden studiert.

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On the filled upRe ₃ B-type in the systems(Zr, Hf)–(Fe, Co, Ni)–O

It is shown that the octahedral voids of the Re₃B-type are partially filled up by oxygen in the above systems. The homogenous ranges ofx of the phases Zr₃CoO _x , Zr₃NiO _x , Hf₃CoO _x , and Hf₃NiO _x are studied.

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Preparation of TeOx–SiO2 film with excellent third-order nonlinear optical properties by electrochemically induced sol–gel method

TeO_x-SiO₂ composite films having third-order nonlinearities were prepared by electrochemically induced sol-gel deposition method on ITO substrate.The third-order optical nonlinearities of the films were measured by Z-scan technique.The third-order nonlinear susceptibilities(χ^（3）) of the as-prepared films are 5.9×10^-7 to 4.29×10^-6esu.The surface morphology and composition of the films were characterized by SEM/EDX,which identified that Te metallic particles well dispersed in TeO_x-SiO₂ gel films.     

Repair of defects created by Ar+ sputtering on graphite surface by annealing as confirmed using ToF‐SIMS and XPS

Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar⁺ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp³ carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the C_x⁻ and C_xH⁻ ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of C_xH₂^+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp³ carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the C_xH⁻ and C_xH₂^+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.     

Thermogravimetric Investigations of Nickel-Oxide Thin Films and Powders

Classical TG analysis of films supported on micro-cover glasses was performed in order to determine the appropriate processing temperature to achieve electrochemically active NiO_xH_y thin films. As deposited films made from three different precursors (Ni-acetate, nitrate and sulphate) and their corresponding powders were also investigated. From dynamic TG measurements the onset decomposition temperature could be determined. It was found out that the starting temperature of the mass change of thin films is approximately 30 degrees lower than that of the powders. A broader decomposition range was also observed for thin films. Furthermore, the isothermal treatment of films deposited on conducting substrate at 270 and 300°C was performed and by cyclic voltametry the importance of temperature and time of heating was proved. Films obtained at higher temperatures (>300°C) are electrochemically inert because of the NiO phase formation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of annealing on the structural,electrical and optical properties of reactively evaporated thin fdlms of indium oxide

Thin films of indium oxide were prepared by thermal reactive evaporation of a mixture of indium oxide and metallic indium. This work is an experimental study of the modifications induced by an annealing treatment, on the structural, electrical and optical properties of indium oxide (In₂O₃). The results show important changes of different parameters determined after annealing. The films obtained after annealing at 350 °C for 3 hours under oxygen atmosphere have a good cristallinity. These films showed a transmittance of more than 80% in the visible region and a conductivity >10³ (Ω.cm)⁻¹.     

Ultrathin cobalt silicide film formation on Si(100)

The interfacial reaction between ultrathin Co film and substrate Si(100) was studied by in situ XPS using monochromatized Al Kα. When the Co is deposited on Si(100) at room temperature, CoSi₂ is formed during the initial stage of Co deposition and then metallic Co starts to grow sequentially. For 8 ML Co deposition on Si(100) the interfacial reaction layer is relatively thin compared with the pure Co overlayer, which is not involved in the interfacial reaction in depth. The Co layers change rapidly to CoSi layers after annealing at 270°C, and then CoSi₂ layers form after annealing at 540°C for 2 min. The CoSi₂ layers are changed to CoSi₂ islands by post‐annealing at >650°C. Copyright © 2003 John Wiley & Sons, Ltd.     

XPS study of the oxidation of nanosize Ni/Si(100) films

The XPS (X-ray photoelectron spectroscopy) study of nickel oxide nanolayers obtained by magnetron sputtering of the metal and its subsequent oxidation in air at different temperatures (400°C and 1000°C) was performed. Silicon(100) was used as a substrate. Surface of the initial Ni/Si structure was shown to contain not only Ni metal, but also the NiO oxide. Annealing at 400°C results in a complete oxidation of the metal film. At a high-temperature annealing (1000°C), nickel interacts both with oxygen and silicon substrate to form NiSi silicide and a composite Ni-Si-O phase in transition layer. Electronconductivity of NiO films is determined by intercrystallite barriers. Activation energies of film electroconductivity in model gases (O₂, Ar, H₂) were found.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.     

Photocatalytic splitting of water under visible-light irradiation over the NiOx-loaded Sm2InTaO7 with 4f-d-d configuration

A new visible-light-response photocatalyst Sm₂InTaO₇ with 4f-d¹⁰-d⁰ configuration crystallized in a cubic system with the space group Fd3m was synthesized by a solid-state reaction method. NiOx-loaded Sm₂InTaO₇ showed high photocatalytic activities for H₂ evolution from pure water under visible light irradiation (λ>400 nm). Changes in the photocatalytic activity with the calcination temperature of Sm₂InTaO₇ and the amount of NiOx loaded indicated that the combination of highly crystallized Sm₂InTaO₇ and a high dispersion of NiOx particles led to high photocatalytic activity. The high photocatalytic performance of NiOx-loaded Sm₂InTaO₇ supported the existing view that the photocatalytic activity correlated with the lattice distortion. Density functional theory calculation indicated that strong dispersion from the hybridized In 5s 5p orbitals at the bottom of the conduction band was responsible for the high activity of photocatalyst Sm₂InTaO₇.