Nanostructured Metal Oxide Thin Films Research Articles

Electron beam evaporated gold doped tungsten oxide nanostructured films for sensor applications

Gas sensors play a vital role in monitoring environmental pollution for human health, safety, and the detection of various gasses in the environment. Nanostructured metal oxide thin films have been widely used in sensor applications owing to their unique properties. In this study, pure and gold (Au) doped nanostructured tungsten trioxide (WO3) films were deposited on glass substrates by electron beam evaporation at room temperature. The microstructure of the WO3 films changed from nanoflakes to nanorods upon variation of the wt% of Au. The sensing properties of WO3 based nanostructure films were measured using a computer-controlled system. The gas sensing results showed that the Au-doped WO3 films exhibited a higher sensitivity than the undoped films. The 15 wt% Au-doped WO3 nanostructure films showed high sensitivity towards ethanol and the response (sensitivity) value was 89. The response and recovery times for 15 wt% Au-doped WO3 were 8 and 10 s, respectively.

Surface Photon‐Engineered Infrared‐Black Metametal Enabled Enhancement of Heat Dissipation

AbstractHeat dissipation is a severe barrier for ever‐smaller and more functionalized electronics, necessitating the continuous development of accessible, cost‐effective, and highly efficient cooling solutions. Metals, such as silver and copper, with high thermal conductivity, can efficiently remove heat. However, ultralow infrared thermal emittance (<0.03) severely restricts their radiative heat dissipation capability. Here, a solution‐processed chemical oxidation reaction is demonstrated for transfiguring “infrared‐white” metals (high infrared thermal reflectance) to “infrared‐black” metametals (high infrared thermal emittance). Enabled by strong molecular vibrations of metal‐oxygen chemical bonds, this strategy via assembling nanostructured metal oxide thin films on metal surface yields infrared spectrum manipulation, high and omnidirectional thermal emittance (0.94 from 0 to 60°) with excellent thermomechanical stability. The thin film of metal oxides with relatively high thermal conductivity does not hinder heat dissipation. “Infrared‐black” meta‐aluminum shows a temperature drop of 21.3 °C corresponding to a cooling efficiency of 17.2% enhancement than the pristine aluminum alloy under a heating power of 2418 W m−2. This surface photon‐engineered strategy is compatible with other metals, such as copper and steel, and it broadens its implementation for accelerating heat dissipation.

Aerosol Chemical Vapor Deposition of One-Dimensional Cu-Doped TiO2 Nanostructured Anodes for High-Rate Lithium Ion Batteries

Energy storage has become increasingly important in recent years due to the rapidly increasing number of electric vehicles (EVs) in use and expanded utilization of intermittent renewable energy sources. Improvements in longevity, energy density, and high rate capability are needed for the next generation of batteries. Lithium-ion batteries (LIBs), the most widely commercialized rechargeable batteries are being used in EVs and some pilot grid-scale storage facilities. One avenue for enhancing the performance of LIBs is the development of novel electrode materials. One such material, titanium dioxide (TiO2) exhibits very high stability during cycling and is capable of ultra-high rate charging and discharging. However, a major drawback to TiO2 is its relatively low electrical conductivity, which limits its performance. Using nanostructured, one-dimensional morphologies the issue of low conductivity can be mitigated. Additionally, metal-doping of TiO2 with various metallic cations such as zinc, copper, or niobium has been shown to increase conductivity as well. Aerosol chemical vapor deposition (ACVD) is an atmospheric pressure technique used to deposit nanostructured metal oxide thin films. In ACVD, a vapor phase organometallic precursor is fed to a reactor and undergoes thermal degradation forming metal oxide monomers. The monomers nucleate to form particles which undergo condensational growth before depositing onto a heated substrate, where the particles sinter into various morphologies. Controlling the rates of these processes using various system parameters leads to the deposition of one-dimensional, columnar structures. Additionally, by introducing two precursors simultaneously doped materials can be synthesized, with the composition controlled by the relative flowrates into the reactor. In this work, we aim to investigate the effect of Cu-doping on the properties and performance of nanostructured TiO2 negative electrodes in LIBs. To achieve this, Cu-doped TiO2 films with compositions between 0-10 at% are synthesized on stainless steel using ACVD and directly utilized as anodes in LIBs. In order to determine the effect of Cu-doping on battery performance a rate capability test is performed by cycling the batteries at progressively higher rates. Additionally, long-term cycling is performed to determine the stability of the electrodes. Additionally, characterization of the lithium diffusion coefficient is performed using both cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). Finally, density function theory (DFT) simulations are performed in order to validate the experimentally measured values for the lithium diffusion coefficient and the electrical conductivity.

Pulsed photonic fabrication of nanostructured metal oxide thin films

Nanostructured metal oxide thin films with a large specific surface area are preferable for practical device applications in energy conversion and storage. Herein, we report instantaneous (milliseconds) photonic synthesis of three-dimensional (3-D) nanostructured metal oxide thin films through the pulsed photoinitiated pyrolysis of organometallic precursor films made by chemical solution deposition. High wall-plug efficiency-pulsed photonic irradiation (xenon flash lamp, pulse width of 1.93 ms, fluence of 7.7 J/cm2 and frequency of 1.2 Hz) is used for scalable photonic processing. The photothermal effect of subsequent pulses rapidly improves the crystalline quality of nanocrystalline metal oxide thin films in minutes. The following paper highlights pulsed photonic fabrication of 3-D nanostructured TiO2, Co3O4, and Fe2O3 thin films, exemplifying a promising new method for the low-cost and high-throughput manufacturing of nanostructured metal oxide thin films for energy applications.

Composite Tin Dioxide-Titanium Dioxide Nanostructured Thin Film Electrodes As Lithium-Ion Anodes

An aerosol-chemical vapor deposition technique (ACVD) was utilized in order to deposit highly oriented, one-dimensional nanostructured metal-oxide thin films. Film morphology was controlled using various system parameters in order to obtained the desired columnar morphology. Tin dioxide (SnO2) was chosen as an electrode material due to its high theoretical charge capacity (790 mA-h-g-1), and titanium dioxide (TiO2) was chosen for its remarkable stability and low volume change during charging. The columnar morphology is particularly well suited to SnO2 as the space between the columns allows for accommodation of the large volume expansion the material experiences during charging. Electrodes of SnO2 columnar nanostructures were first synthesized using ACVD by depositing the structures directly on to the current collector. Depositing directly onto the current collector eliminates the need for binding agents and conductive additives during battery fabrication. Then a layer of TiO2 was deposited on the surface of the SnO2 columns using atomic layer deposition. A variety of column heights, ranging from 500 nm to 2 um, and TiO2 layer thickness, ranging from no TiO2 to a 100 nm layer, were synthesized and their electrochemical properties investigated. For all electrochemical characterization experiments, Swagelok-type coin cells were fabricated using lithium foil as a counter electrode and 1M LiPF6 in 50/50 (v/v) EC/DEC as an electrolyte. Optimal electrochemical performance was observed in electrodes with a height of 800 nm and a 15 nm layer of TiO2. A rate capability test was performed to determine how the capacity of the electrodes changed at charging rates ranging from 100-2000 mA-g-1. A stable capacity of 410 mA-h-g-1 was obtained at a charge rate 1000 mA-g-1; rapid capacity fade was observed at higher rates. Galvanostatic charge-discharge was performed for each cell for 100 cycles or until failure at a charge rate of 400 mA-g-1, corresponding approximately to a charge rate of C/2. For the optimal electrode an initial irreversible capacity of 1164 mA-h-g-1 was observed as well as a stable capacity of 530 mA-h-g-1 after 100 cycles. This demonstrates a low cost synthesis of high performance anodes which provides an alternative to conventional electrode synthesis.

Model based prediction of nanostructured thin film morphology in an aerosol chemical vapor deposition process

The aerosol chemical vapor deposition (ACVD) process has been demonstrated as a promising approach to the single step synthesis of nanostructured metal oxide thin films. Multiple process parameters control the nanostructure morphology and the growth of thin films. This work focuses on utilizing a simulation based approach to understand the role of these parameters in governing the morphology of the thin film. A finite element based computational fluid dynamics model, coupled with a discrete-sectional aerosol model, and a boundary layer diffusion and sintering model has been formulated to predict the evolution of particle size distribution and the morphology of the synthesized nanostructured film. The morphology predicted by the model was validated by experimental observations. The model enables scale up and wider application of the ACVD process and can be extended to other gas phase deposition systems.

Rapid growth of vertically aligned tungsten oxide nanostructures by flame vapor deposition process

Flame vapor deposition system embedded with a wire feeder was developed for the first time to guarantee the precise control of wire feed rate. Vertically aligned nanowire, nanotube, multi-tube and bush-like tungsten oxide nanostructures were successfully obtained in this system. The feasible growth mechanisms of these nanostructures were proposed. This research offers a robust and fast approach to prepare nanostructured metal oxide thin films with controlled morphologies.

Slit-based supersonic microplasma jets: Scalable sources for nanostructured thin film deposition

Slit-based, hollow cathode microplasma jets operating in under-expanded supersonic flow were investigated as spray deposition sources to realize nanostructured metal oxide thin films. Design of the slit cathode, its operation (e.g., IV characteristics, fluorescence imaging of supersonic flow shock structures, etc.), and companion CuO nanowire deposition experiments are discussed. Overall, this work demonstrates that slit-based, flow-through microplasmas are a promising way to scale up hollow cathode discharges for large area deposition of thin films at high pressures (>10 Torr).

Electric field assisted aerosol assisted chemical vapor deposition of nanostructured metal oxide thin films

Thin films of vanadium dioxide were deposited using a novel electric field assisted chemical vapor deposition methodology onto glass and gas sensor substrates. Electric fields were generated during the deposition reaction by applying a potential difference across the inter-digitated electrodes of the gas sensor substrate or buy applying an electric field between two transparent conducting oxide coated glass substrates. The deposited films were analyzed and characterized using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, atomic force microscopy and contact angle measurements. It was found that applying an electric field led to large changes in film microstructure, preferential orientation and changes in the film growth rate. This led to significant changes in materials properties such as increased surface roughness and enhanced wetting behaviour. Electric field-assisted chemical vapour deposition shows great promise as a method for nano-structuring and tailoring the properties of metal oxide thin films.

Electric field assisted aerosol assisted chemical vapour deposition of nanostructured metal oxide thin films

Nanostructured thin films of tungsten, vanadium and titanium oxides were deposited on gas sensor substrates from the electric field assisted chemical vapour deposition reaction of tungsten hexaphenoxide, vanadyl acetylacetonate and titanium tetraisopropoxide respectively. The electric fields were generated by applying a potential difference between the inter-digitated electrodes of the gas sensor substrates during the deposition. The deposited films were characterised using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The application of an electric field, encouraged the formation of interesting and unusual nanostructured morphologies, with a change in scale length and island packing. It was also noted that crystallographic orientation of the films could be controlled as a function of electric field type and strength. The gas sensor properties of the films were also examined; it was found that a two to three fold enhancement in the gas response could be observed from sensors with enhanced morphologies compared to control sensors grown without application of an electric field.

Synthesis, characterization and investigation of the thermal behaviour of six novel polynuclear cobalt and copper complexes for potential application in MOCVD

AbstractNew tetranuclear complexes of copper and cobalt have been prepared under ambient conditions from corresponding metal acetates in acetone, using triethanolamine and diethanolamine as the ligands. The complexes have been characterized by infrared spectroscopy, mass spectroscopy, elemental analysis and thermal analysis. The mass spectra of the complexes show that the complexes retain the acetate moiety in their structures. Simultaneous thermogravimetric and differential thermal analysis (TGA–DTA) reveal that the complexes are solids that sublime over the temperature range 50–100 °C, under atmospheric pressure. The TGA–DTA curves reveal that the complexes retain carbon at temperatures as high as 500 °C. The presence of carbon is known to limit the mobility of growth species for oxides, restricting them to nanometersized crystals. Thus, the complexes have potential applications as precursors in the growth of nanostructured metal oxide thin films under specific CVD conditions. Because of their low sublimability, the complexes are prospective candidates as precursors for low‐temperature growth of multilayer oxide thin films where the thickness of individual layers needs to be controlled at nanometer level and for introducing dopants at low concentrations by MOCVD technique. Copyright © 2006 John Wiley & Sons, Ltd.

Surface Functionalization of Porous Nanostructured Metal Oxide Thin Films Fabricated by Glancing Angle Deposition

We report the application of solution- and vapor-phase siloxane-based methods for tailoring the surface chemistry/properties of highly porous, nanostructured thin films fabricated using glancing angle deposition (GLAD). The GLAD technique produces high surface area films consisting of isolated columns and provides complete control over the film/column morphology. In the present study, the chemical tunability of a variety of metal oxide GLAD films was investigated using solution-based and vapor-phase surface functionalization methodologies. The surface properties and structures of the treated and untreated films were investigated using scanning electron microscopy (SEM), advancing aqueous contact angle measurements, cyclic voltammetry, and X-ray photoelectron spectroscopy (XPS). Results indicate that the surface chemistry of metal oxide GLAD films could be tailored by either method; however, chemical reactivity depends strongly on the metal oxide film material. Chemical tunability is demonstrated through the covalent tethering of numerous chemical moieties onto the exposed and interior surfaces of metal oxide GLAD films of varied structural motifs. Through careful choice of surface modifier, the present derivatization methods afford a full range of aqueous wettability from hydrophilic to superhydrophobic without compromising film structure. These functionalized, nanoconstructed films demonstrate a high degree of tunability over both structural and surface properties, making them well suited for diverse applications such as optical filters or sensors.

Synthesis and Characterization of Functional Nanostructured Metal Oxide Thin Films

not Available.

Aqueous purpose-built nanostructured metal oxide thin films

A novel concept in materials chemistry as well as an aqueous low-temperature thin film growth technique has been developed to create a new generation of smart and functional metal oxide thin film materials. These materials are modelled, designed and engineered to match the physical and structural requirements of their applications. This concept is well-sustained by a thermodynamic model monitoring the nucleation, growth and ageing processes through the chemical and electrostatic control of the interfacial free energy. It allows to monitor the size of nano and microparticles, their surface morphology and their orientation onto substrates as well as the ability to thermodynamically stabilize metastable crystal phases. This template- and surfactant-free aqueous chemical growth method allows generation of, at large scale and low-cost, advanced metal oxides nano- and micro-particulate multilayered thin films with complex architectures. It includes 3-dimensional highly oriented crystalline arrays of ferric oxides nanorods, zinc oxide nanorods, microrods, microtubes, and nanowires. Other applications include nanocomposite thin films consisting of chromium and iron sesquioxide and nanoporous ruthenium/ruthenium oxide thin film grown at low temperature from aqueous solution onto various substrates.

Reductive Electron Transfer Quenching of MLCT Excited States Bound To Nanostructured Metal Oxide Thin Films

The ruthenium compounds Ru(deeb)(bpz)2(PF6)2, Ru(deeb)2(bpz)(PF6)2, and Ru(deeb)2(dpp)(PF6)2, where deeb is 4,4‘-(CO2CH2CH3)2-2,2‘-bipyridine, bpz is 2,2‘-bipyrazine, and dpp is 2,3-bis(2-pyridyl)pyrazine, have been prepared, characterized, and anchored to mesoporous nanoparticle thin films comprised of the wide band gap semiconductor TiO2 or the insulator ZrO2. The metal-to-ligand charge-transfer (MLCT) excited states of these compounds are potent photooxidants (E°(RuII*/+) > +1.0 V vs SCE) with long lifetimes (τ > 1 μs) that efficiently oxidize iodide and phenothiazine with rate constants that approach the diffusion limit in acetonitrile. Photogalvanic cells based on the sensitized TiO2 materials yield photocurrent action spectra that agree well with the Ru(II) absorptance spectra. The photocurrent efficiency was very low, φ < 10-4. Transient absorption data show that neither the excited nor the reduced state of the ruthenium compounds efficiently inject electrons into the TiO2 particles. The cage escape yields following excited-state electron transfer are approximately 2/3 lower in the mesoporous thin films than in fluid solution. Intermolecular energy transfer across the nanoparticle surfaces is manifest in a second-order component to the excited-state relaxation kinetics.