Mixed Oxide Films Research Articles

Photoelectrochemical behavior of mixed ZnO and GaN (ZnO:GaN) thin films prepared by sputtering technique

Mixed zinc oxide and gallium nitride (ZnO:GaN) thin films with significantly reduced bandgaps were synthesized by using zinc oxide and gallium nitride target at 100°C followed by post-deposition annealing at 500°C in ammonia for 4h. All the films were synthesized by RF magnetron sputtering on Fluorine-doped tin oxide-coated glass. We found that mixed zinc oxide and gallium nitride (ZnO:GaN) thin films exhibited significantly reduced bandgap, as a result showed improved PEC response, compared to ZnO thin film. Furthermore, mixed zinc oxide and gallium nitride (ZnO:GaN) thin films with various bandgaps were realized by varying the O2 mass flow rate in mixed O2 and N2 chamber ambient.

Technology and Application of Transition Metal Oxide of W-V-O as Functional Layers and NiO Thin Films as Counter Electrode Material in Electrochromic “Smart Windows”

Abstract The present study is related to preparation and investigation of mixed W-V-O films, deposited on conductive glass substrates by atmospheric pressure chemical vapor deposition. The presence of lower-temperature precursor V(CO) 6 lead to faster growing of the mixed oxide film. The results show two times higher growth-rate compared to single oxide of WO 3 . The color efficiency calculated is 20 cm 2 /C, optical modulation 65.2%. Vibrational spectra studied by Raman and FTIR spectroscopy show Raman peaks and absorption bands revealing monoclinic WO 3 and orthorhombic V 2 O 5 phases, separately existing in the mixed oxide film structure. The surface morphology is observed by AFM. Films transmittance and reflectance characterization are performed. For the counter electrode in the EC, NiO films are deposited electrochemically. The UV-VIS-NIR optical measurements performed in the spectral range of 300 - 1000 nm show that films possess transmittance in the range of 70% - 85%. This high transmittance of the counter electrode film would contribute to the needed high initial optical transmittance of the “smart window”.

Ternary Ti–Mo–Ni mixed oxide nanotube arrays as photoanode materials for efficient solar hydrogen production

To date, most studies on the fabrication and development of photoelectrodes for solar-fuel generation have been based on simple binary systems with limited success. However, ternary systems have not been explored extensively although they can offer more possibilities for band gap and band alignment tuning that allow the development of more efficient photoelectrochemical systems. Herein, we report on the growth of a novel ternary oxide photoanode material composed of self-ordered, vertically oriented nanotube arrays of titanium-molybdenum-nickel mixed oxide films via the anodization of a Ti-Mo-Ni alloy in an electrolyte solution of formamide containing NH4F at room temperature, followed by annealing in an air atmosphere. The nanostructure topology was found to depend on both the anodization time and the applied voltage. Our results demonstrate the ability to grow mixed oxide nanotube array films that are several microns thick. The Ti-Mo-Ni mixed oxide nanotube array films were utilized in solar-spectrum water photoelectrolysis, demonstrating a photocurrent density of 2.1 mA cm(-2) and a ∼10 fold increase in the photoconversion efficiency under AM 1.5 illumination (100 mW cm(-2), 1 M KOH) compared to pure TiO2 nanotubes fabricated under the same conditions. This enhancement in the photoconversion efficiency can be related to the synergistic effects of Ni and Mo alloying and the unique structural properties of the fabricated nanotube arrays.

A Self-Assembled Two-Layer Structured WO3/TiO2-x Mixed Film with Improved Electrochromic Capacities

Electrochromics are a promising avenue for energy savings in tropical climates where heating of buildings is largely by transmission of infrared light through windows, causing 40% of their electrical demand to be used on air-conditioning. One technique to improve the electrochromic properties of WO3 films is to dope with a second transition metal oxide. In the present work a mixed WO3/TiO2-x film was prepared by a single step hydrothermal method. XRD investigations suggested that the doping was achieved by replacement of W6+ by Ti4+ ions in the WO3 lattice structure, rather than discrete phases of WO3 and TiO2. The composite film presented a large light modulation ability of 67% at 632.8 nm, twice that of an equivalent pure WO3 film, was well adhered to the substrate and showed good electrochromic reversibility switching rates of less than 26 s. In the colored state the transmittance in the visible light range of the mixed transition metal oxide film was below 5%, whilst in the bleach state this exceeded 70%. Electrochemical impedance measurements suggested that the improvement in electrochromic properties was due to the TiO2 doping reducing both the film's electrical resistance and its resistance to diffusion of ions within the film.

Lithium-molybdate nanostructures grown on the Mo(001) surface

Ordered LiMo mixed-oxide films of different compositions have been grown on a Mo(001) surface and analysed by means of scanning tunnelling microscopy, low-energy-electron-diffraction and cathodoluminescence spectroscopy. Starting from a disordered LixO ad-layer grown at room temperature, a scheelite-type Li2MoO4 phase develops on the Mo surface after annealing to 700K. The building blocks of this structure are regular nanorods of approximately 30nm length, which exhibit strong light emission in the green spectral range upon electron injection. Further annealing induces a restructuring of the film that evolves into various mixed-oxide phases of decreasing Li content. The Li fully desorbs from the surface above 1000K, leaving behind a nano-crystalline Mo-oxide. Our approach demonstrates that ternary LiMo oxides of high structural quality can be grown as thin films, making them accessible to conventional surface science techniques without charging problems.

Preparation and characterization of thin film thermistors of metal oxides of manganese and vanadium (Mn-V-O)

Thin films of mixed metal oxides of manganese and vanadium (Mn-V-O) have been prepared by electron beam evaporation technique for the first time. Chemical composition, surface morphology and electrical and optical properties of thin films have been studied using energy dispersive analysis of x-ray (EDAX), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-VIS-NIR spectrometer. It is observed by X-ray diffraction analysis that all the thin films of Mn-V-O are amorphous. The XPS analyses indicate the core level binding energies correspond to Mn (2p), V (2p) and O (1s). The study of electrical properties clearly show that all the thin films follow a typical characteristics of negative temperature coefficient (NTC) resistivity, with activation energy varying from 0.274 to 0.358eV, which is attributed to small polaron hopping. The observed temperature of coefficient of resistivity (TCR) is found to be comparable with TCR of many of the known thermistor materials. All the thin film samples are found to have optical band gaps varying from 2.66 to 3.17eV which are marginally different from the band gaps of MnO and V2O5. The optical absorption characteristics in near infrared region show enhanced absorption compared to visible region which are attributed to presence of defect states due to V4+, oxygen ion vacancies and energy states due to polarons.

High temperature wear of cermet particle reinforced NiCrBSi hardfacings

The aim of the current study was to investigate erosive and impact/abrasive wear behaviour of TiC–NiMo and Cr3C2–Ni reinforced NiCrBSi hardfacings at temperatures up to 700°C.Coatings were produced using plasma transferred arc cladding process. It was shown that the high temperature wear behaviour of TiC–NiMo and Cr3C2–Ni NiCrBSi hardfacings is influenced by oxidation. The formation of mechanical mixed layers and oxide films was observed for both investigated coatings. TiC–NiMo and Cr3C2–Ni reinforced hardfacings show high wear resistance at all testing temperatures for both impact/abrasion and erosion conditions.

Vanadium and Titanium Mixed Oxide Films: Synthesis, Characterization and Application as Ion Sensor

Vanadium/titanium mixed oxide films were produced using the sol-gel route. The structural investigation revealed that increased TiO2 molar ratio in the mixed oxide disturbs the V2O5 crystalline structure and makes it amorphous. This blocks the TiO2 phase transformation, so TiO2 stabilizes in the anatase phase. In addition the surface of the sample always presents larger amounts of TiO2 than expected, revealing a concentration gradient along the growth direction. For increased TiO2 molar ratios the roughness of the surface is reduced. Ion sensors were fabricated using the extended gate field effect transistor configuration. The obtained sensitivities varied in the range of 58 mV/pH down to 15 mV/pH according to the composition and morphology of the surface of the samples. Low TiO2 amounts presented better sensing properties that might be related to the cracked and inhomogeneous surfaces. Rising the TiO2 quantity in the films produces homogeneous surfaces but diminishes their sensitivities. Thus, the present paper reveals that the compositional and structural aspects change the surface morphology and electrical properties accounting for the final ion sensing properties of the V2O5/TiO2 films.

V2O5/WO3 Mixed Oxide Films as pH-EGFET Sensor: Sequential Re-Usage and Fabrication Volume Analysis

A vanadium and tungsten mixed oxide was deposited onto glassy carbon substrates and used as pH sensor in extended gate field effect transistor (EGFET) devices. WO3 at a molar ratio of about 5% was mixed with V2O5 by means of the sol-gel method. The main focus of this investigation was to determine the operation conditions for the best response of the device and to propose the mechanism involved in the sensor response. The use of either original or reused films were employed and the importance of the total volume of the starting solution was also examined. The time response of the V2O5/WO3-pH-EGFET sensor is due to a deprotonation mechanism of vanadium and tungsten oxide, similarly to a discharging capacitor. The loss of protons by the oxide film depends on the time it remains immersed in the buffer solution and this process is accelerated upon raising the pH value. The increase of the films fabrication volume reduces the importance of the changes of the surface charges compared to the charges of the bulk, leading to less sensitive and less stable sensor response. Therefore, the smaller the amount of material used, the better the sensing properties of the device.

A structured catalyst based on cobalt phthalocyanine/calcined Mg–Al hydrotalcite film for the oxidation of mercaptan

A structured catalyst has been fabricated by immobilizing cobalt phthalocyanine tetrasulfonate (CoPcS) on a mixed metal oxide (denoted as MMO) film, which exhibits excellent activity, stability and recyclability for mercaptan sweetening. Scanning electron microscopy (SEM) images show that the structured catalyst is composed of MMO nanoflakes whose ab-plane is perpendicular to the Al substrate, with desired mechanical strength and high adhesion to the substrate. In addition, in situ IR spectra and carbon dioxide temperature programmed desorption (CO2-TPD) reveal that the moderate basic site is overwhelming in the CoPcS/MMO structured catalyst, while the strong basic site predominates in the corresponding CoPcS/MMO powder catalyst. It was found that the structured catalyst exhibits high conversion (85.7%) for the oxidation of mercaptan to disulphide, markedly higher than that of the corresponding powder catalyst (38.7%), as a result of the high exposure of active species as well as the synergistic effect between the oxidation center (CoPcS) and the moderate basic site. In addition, the structured catalyst shows superior catalysis-regeneration performance, which facilitates its repeatable and cyclic usage over a long period. Therefore, this work provides a facile and effective method for the fabrication of structured catalyst with high catalytic activity and stability, as well as recyclability, which can be used as an eco-friendly catalyst for the sweetening process in the petroleum refining industry.

Electrochromic properties of nickel oxide and mixed Co/Ni oxide films prepared via sol–gel route

The Ni oxide and mixed Co/Ni oxide films were prepared by sol–gel dip coating method at optimum conditions. The XRD analysis reveals the pure and Co mixed nickel oxide films to be in amorphous state. The field emission SEM images reveal nanopore like structure for Ni oxide film and well defined grains with pores for Ni oxide films containing 5wt.% of Co. Electrochromic properties have been studied using cyclic voltammetric (CV) and in situ spectro-electrochemical techniques. The pure and cobalt mixed (5wt.%) Ni oxide films exhibit anodic/cathodic diffusion coefficient of 4.93±0.14/3.74±0.10×10−10cm2/s and 10.00±0.24/7.60±0.20×10−10cm2/s respectively after 300cycles. The cobalt mixed (5wt.%) Ni oxide films exhibit the bleached/coloured state transmission of 90.42/7.21% with a photopic constrast ratio of 12.54 and the colouration and bleaching time were 5.9 and 2.4s respectively. The addition of cobalt beyond 5% leads to poor transparency and inhibited electrochromic switching character.

Compositional and metal-insulator transition characteristics of sputtered vanadium oxide thin films on yttria-stabilized zirconia

Vanadium dioxide (VO2) thin films have been shown to undergo a rapid electronic phase transition near 70 °C from a semiconductor to a metal, making it an interesting candidate for exploring potential application in high speed electronic devices such as optical switches, tunable capacitors, and field effect transistors. A critical aspect of lithographic fabrication in devices utilizing electric field effects in VO2 is the ability to grow VO2 over thin dielectric films. In this article, we study the properties of VO2 grown on thin films of Yttria-Stabilized Zirconia (YSZ). Near room temperature, YSZ is a good insulator with a high dielectric constant (\(\epsilon _{\rm r} > 25\)). We demonstrate the sputter growth of polycrystalline VO2 on YSZ thin films, showing a three order resistivity transition near 70 °C with transition and hysteresis widths of approximately 7 °C each. We examine the relationship between chemical composition and transition characteristics of mixed phase vanadium oxide films. We investigate changes in composition induced by low temperature post-deposition annealing in oxidizing and reducing atmospheres, and report their effects on electronic properties.

Electrochromic and Optical Study of Atmospheric Pressure Chemical Vapour Deposition MoO<SUB>3</SUB>–Cr<SUB>2</SUB>O<SUB>3</SUB> Films

Electrochromism (EC) is a phenomenon in which materials are able to change their optical properties in a reversible and persistent way under the action of a voltage pulse. The studied MoO3-Cr2O3 films are obtained by atmospheric pressure CVD. Mixing MoO3 films with Cr2O3 is expected to enhance optical transparency and to modulate electrochromic properties of MoO3 films. In the present work, the study is focused on the morphological, structural and optical properties of MoO3-Cr2O3 films as a function of annealing temperatures. Raman spectroscopy and optical spectrophotometry are used for the film characterization. The mixed oxide films obtained on ordinary glass substrates show transmittance values in the range of 70-80%. Surface morphology is analyzed by SEM and AFM methods. The microanalysis of MoO3-Cr2O3 films reveals uniform distribution of the elements, which is a sign of homogeneous structure.

Pulsed laser deposition of (WO 3) 1 − x (Nb 2O 5) x thin films: Characterization and gasochromic studies

A series of (WO 3) 1 − x (Nb 2O 5) x (x = 0, 0.05, 0.1 and 0.15) mixed oxide films were fabricated by pulsed laser deposition (PLD) at 27 Pa oxygen partial pressure on ITO glass substrates. The thickness of the (WO 3) 1 − x (Nb 2O 5) x thin films is about 350 ± 30 nm and their surface has a uniform morphology. A layer of platinum (Pt) was then sputtered onto the surface of the film. The hydrogen gas sensing performance of Pt catalyst activated (WO 3) 1 − x (Nb 2O 5) x thin films were investigated. The cycling of the coloration was obtained from UV–vis spectra. Gasochromic coloration of (WO 3) 1 − x (Nb 2O 5) x thin films were investigated at room temperature in H 2–N 2 mixtures containing 1–100 mol% of H 2. The results show that the shortest response time of (WO 3) 1 − x (Nb 2O 5) x/Pt hydrogen sensor is within 30 s and the highest transmittance change (ΔT) varies from 20% to 30%.

Strain-induced formation of ultrathin mixed-oxide films

By means of scanning tunneling microscopy, Auger spectroscopy, and density-functional theory, we have identified a different strain-relaxation mechanism taking place in ultrathin CaO films grown on Mo(001). Whereas CaO films are amorphous at low growth temperature due to the substantial lattice mismatch with the support, a crystalline phase develops upon annealing to 1000 K. This phase is characterized by a sharp (2 \ifmmode\times\else\texttimes\fi{} 2) pattern in low-energy electron diffraction and displays wide, atomically flat terraces in scanning tunneling microscopy images. The phase transition is initiated by the diffusion of Mo from the support into the film, where it replaces 25% of the Ca ions. The resulting rocksalt-type Ca${}_{3}$MoO${}_{4}$ structure has a negligible lattice mismatch with the Mo(001), enabling the growth of extended, defect-free oxide patches. The oxidation of Mo atoms from the support provides the thermodynamic stimulus for the phase transition. For MgO films grown on the same Mo(001) surface, no relevant intermixing is revealed at the interface, most likely because of the smaller lattice mismatch between both systems.

Preparation and characterization of ZnO–TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO–TiO2 thin films. For comparison, pure TiO2 and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400–750°C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400°C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn2TiO4, anatase TiO2 and amorphous fraction. The XRD analysis presumes that Zn2TiO4 becomes a favored phase at the highest annealing temperature of 750°C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO–TiO2 films have been compared with those of single component films (ZnO and TiO2). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.

Electronic Structure of Magnesia−Ceria Model Catalysts, CO2Adsorption, and CO2Activation: A Synchrotron Radiation Photoelectron Spectroscopy Study

We have studied the electronic properties of single crystal based ceria and magnesia−ceria model catalysts, the CO2 adsorption, and the CO2-induced reoxidation of these systems by synchrotron radiation photoelectron spectroscopy (SR-PES). All model systems were prepared starting from a fully stoichiometric and well-ordered CeO2(111) film grown on Cu(111). Different magnesia−ceria mixed oxide films were prepared by physical vapor deposition (PVD) of magnesium, oxygen treatment, and subsequent annealing. The preparation procedure was varied to obtain samples with different oxidation state, structure, and surface composition. Different carbon-containing species were identified, including surface carbonates formed in the vicinity of Mg2+ and Ce3+/4+ and surface carboxylates. The presence of Mg2+ was observed to strongly enhance carbonate formation but suppress the formation of carboxylates. Changes in the oxidation state of ceria upon CO2 exposure were monitored with highest sensitivity by resonant photoelect...

Control of the optical properties of silicon and chromium mixed oxides deposited by reactive magnetron sputtering

The development of mixed-oxide thin films allows obtaining materials with better properties than those of the different binary oxides, which makes them suitable for a great number of applications in different fields, such as tribology, optics or microelectronics. In this paper we investigate the deposition of mixed chromium and silicon oxides deposited by reactive magnetron sputtering with a view to use them as optical coatings with an adjustable refractive index. These films have been characterized by means of Rutherford backscattering spectrometry, Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy and spectroscopic ellipsometry so as to determine how the deposition conditions influence the characteristics of the material. We have found that the deposition parameter whose influence determines the properties of the films to a greater extent is the amount of oxygen in the reactive sputtering gas.

Oxide-Based Electrochromics: Advances in Materials and Devices

ABSTRACTElectrochromic (EC) devices are able to vary their throughput of visible light and solar energy by the application of a voltage. They are of much interest for “smart” windows in buildings and are able to create energy efficiency, occupant well being, and security. This paper gives a survey over oxide-based EC device technology and also presents some recent advances regarding EC thin films of mixed metal oxides, nanoparticle-containing electrolytes to join these films, and metal-based transparent electrical conductors needed to apply the voltage.

Atomic-Layer-Deposited Dielectric Thin Films on a Cu Clad Laminate Substrate for Embedded Metal–Insulator–Metal Capacitor Applications in Printed Circuit Boards

This study examined the interfacial reactions between Cu clad laminate (CCL) substrates and atomic-layer-deposited (ALD) , and films and their effects on the electrical properties of the films. The Cu and Pt substrates with thick sputtered Cu and Pt layers on were also used as references. Serious interfacial reactions, such as defective interfacial layer growth and diffusion into the film, occurred in the ALD films grown on the CCL substrates, which deteriorated electrical properties of the films. Although higher growth temperatures improved the properties of the ALD film due to the lower concentrations of residual impurities in the films, the interfacial reactions became increasingly severe. Conversely the ALD films grown on the CCL substrates showed improved electrical properties as well as suppressed interfacial reactions and a sharp interface with the substrate compared to those of the ALD films. This was confirmed by X-ray photoelectron spectroscopy analysis of ALD , and mixed oxide films. Effective interfacial reaction barrier properties of an ALD film were also demonstrated by an electrical examination of stacked films with and .