Alumina coating on dense tungsten powder by fluidized bed metal organic chemical vapour deposition

In order to study the feasibility of coating very dense powders by alumina using Fluidized Bed Metal Organic Chemical Vapour Deposition (FB-MOCVD), experiments were performed on a commercial tungsten powder, 75 microm in median volume diameter and 19,300 kg/m3 in grain density. The first part of the work was dedicated to the experimental study of the tungsten powder fluidization using argon as carrier gas at room temperature and at 400 degrees C. Due to the very high density of the tungsten powder, leading to low initial fixed bed heights and low bed expansions, different weights of powder were tested in order to reach satisfactory temperature profiles along the fluidized bed. Then, using argon as a fluidized bed former and aluminium acetylacetonate Al(C5O2H7)3 as a single source precursor, alumina thin films were deposited on tungsten particles at a low temperature range (e.g., 370-420 degrees C) by FB-MOCVD. The influence of the weight of powder, bed temperature and run duration was studied. Characterizations of the obtained samples were performed by various techniques including scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS) analyses, Field Emission Gun SEM (FEG-SEM) and Fourier Transform InfraRed (FT-IR) spectroscopy. The different analyses indicated that tungsten particles were uniformly coated by a continuous alumina thin film. The thickness of the film ranged between 25 and 80 nm, depending on the coating conditions. The alumina thin films were amorphous and contained carbon contamination. This latter may correspond to the adsorption of species resulting from incomplete decomposition of the precursor at so low deposition temperature.     

Preparation of ferroelectric BaTiO3 thin films by metal organic chemical vapour deposition

Polycrystalline BaTiO₃ thin films have been successfully prepared on (100) silicon substrates at temperatures under 600° C by metal organic chemical vapour deposition using barium acetylacetonate and diisopropoxy-titanium-bis-(acetylacetonate). To vaporize the barium acetylacetonate, which is nonvolatile under 300° C and thermally unstable, an ultrasonic spraying technique was used. The substrate temperature had a great influence on the structure and composition of films and the single-phase BaTiO₃ films could be prepared at 500° C. At temperatures above 550° C the reaction between the film and the silicon substrate occurred to a large extent. The polarization-electric field (P-E) hysteresis loops and counter-clockwise direction of hysteresis in the high-frequency (1 MHz)C-V characteristics indicate that the BaTiO₃ films deposited on silicon using the present method are ferroelectric.     

Thin functional films by combustion chemical vapour deposition (C-CVD)

The use of the atmospheric pressure C-CVD (combustion chemical vapour deposition) process for the deposition of thin functional layers on float glass and plastics is described. We will give an overview on the variety of materials that can be deposited and some examples, like SiO₂, WO_x and Ag, are presented in more detail with potential applications.     

Thin tin oxide films of low conductivity prepared by chemical vapour deposition

Homogeneous SnO₂ films were produced from dibutylin diacetate by chemical vapour deposition at rates of 10–30 nm min^?1. The films obtained had conductiveties between 3 and 25Ω^?1 cm^?1 and they showed a high quantum efficiency for dye sensitization. Under various conditions a linear dependence of the thickness and resistivity of the films on deposition time was observed. The transmission of most of the films was greater than 90%. SnO₂ films with a thickness of more than 500 nm exhibit absorption. The refractive index of these films, as determined by UV-visible interference measurements in reflection, is between 1.8 and 2.2 in the wavelength range 300–860 nm and agrees well with the refractive index determined from interference microscope measurements. Heat treatment of the films exposed to air lowers their conductivity and refractive indices.     

Thin molybdenum oxide films produced by molybdenum pentacarbonyl 1-methylbutylisonitrile with plasma-assisted chemical vapor deposition

Molybdenum oxide thin films were prepared by plasma-enhanced chemical vapor deposition of molybdenum pentacarbonyl 1-methylbutylisonitrile. This precursor is an interesting alternative for the commonly used molybdenum hexacarbonyl, because the substance is liquid at room temperature, offers sufficient volatility and stability to air and water. The film growth was monitored in situ by a soft X-ray reflectivity measurement. The films were deposited with different plasma gases (hydrogen and oxygen) under different conditions and analysed by Auger electron spectroscopy, X-ray diffraction and spectral ellipsometry.     

SiC fibre by chemical vapour deposition on tungsten filament

A CVD system for the production of continuous SiC fibre was set up. The process of SiC coating on 19 μ m diameter tungsten substrate was studied. Methyl trichloro silane (CH₃SiCl₃) and hydrogen reactants were used. Effect of substrate temperature (1300–1500°C) and concentration of reactants on the formation of SiC coating were studied. SiC coatings of negligible thickness were formed at very low flow rates of hydrogen (5 × 10⁻⁵ m³/min) and CH₃SiCl₃ (1.0 × 10⁻⁴ m³/min of Ar). Uneven coatings and brittle fibres were formed atvery high concentrations of CH₃SiCl₃ (6 × 10⁻⁴ m³/min of Ar). The flow rates of CH₃SiCl₃ and hydrogen were adjusted to get SiC fibre with smooth surface. The structure and morphology of SiC fibres were evaluated.     

Thin tellurium films prepared by partially ionized vapour deposition

The effects of partially ionized vapour deposition on the morphology of tellurium films on KBr substrates were investigated. Compared with films formed by conventional neutral vapour deposition, films prepared by partially ionized vapour deposition show several pronounced structural features: (1) enhanced surface coverage on the substrate; (2) disappearance of the separate tips in the shape of a swallow's tail which grow on the end of the crystallites formed by neutral vapour deposition; (3) almost no decoration effect along the step line of the cleavage face of KBr substrates. Enhanced surface coverage of the tellurium film also occurred on glass and mica substrates.     

Thin organic films by atmospheric-pressure ion deposition

Interest in thin films of functional organic materials has increased enormously in recent years because of the wide range of possible applications. Here we report an experimental setup for processing various organic materials into thin structured films under atmospheric pressure. The technique is based on an electrospray process. Microdroplets are initially formed and dried, generating ions that are extracted by electrostatic lenses. Thin structured films are then produced by the deposition of the resulting ion beam onto a moveable target. The technique offers several interesting features, including precise control of film thicknesses. We have also made experiments to investigate structured deposition, this being the first step towards the production of thin films where in all three dimensions the chemical composition can be chosen at will. This might provide a simple approach towards creating thin structured films and composites that are currently unattainable.     

Low temperature deposition of hexagonal BN films by chemical vapour deposition

Transparent hexagonal BN films were deposited onto copper substrates from the reactant gas BCl₃-NH₃-H₂ at temperatures in the range 250–700°C. The lowest deposition temperature of the films was about 250°C. The films deposited at temperatures below 450°C were unstable in moist atmosphere and devitrified; a 20%–30% decrease in weight was observed when these films were heated above 600°C in an argon atmosphere. In contrast, the films deposited at temperatures above 600°C were very stable, decreased in weight by 1%–2% on heating and were stable in air at temperatures below 750°C.     

Formation of amine functionalized films by chemical vapour deposition

Thermally Activated Chemical Vapour Deposition (TA-CVD) has been used for the biofunctionalization of silicon substrates, among others. This technique uses 3-aminopropyltriethoxysilane as organometallic precursor. The deposited films show biofunctional properties, with reactive amines on the surface, as it was shown by FTIR and confocal microscopy. In this work, the influence of the deposition parameters in the microstructure and functionality of the films was investigated. Antibodies were immobilized on the films that had higher and more homogeneous distribution of amines. The confocal microscopy images show that the amines react with the antibodies and that these biomolecules keep their biological functionality.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Undoped and indium-doped CdS films prepared by chemical vapour deposition

Undoped and In-doped films of CdS were deposited at different temperatures by the chemical vapour deposition technique on glass and In-coated (30 nm) glass, respectively. Both kinds of film present a columnar microstructure, low porosity and good adherence to the substrate. The doped films have higher electron mobility values compared with the undoped ones. Shifts in the transmission spectra (Moss-Burstein effect) were observed with increased doping. Small crystals grew over the doped films during the deposition stage, mainly at the higher substrate temperatures.     

The role of CH4 in metal organic chemical vapour deposition of GaAs

A study of the growth of GaAs in the metal organic chemical vapour deposition system over a wide range of temperatures (743–1023 K) and AsH₃ to trimethylgallium (TMG) pressure ratios (6–40) shows that the process is not affected by the addition of CH₄ to the gas phase. This holds true not only for the rate of deposition but also for the morphology of the films and their electrical and photoluminescence characteristics. It is argued that this result is a direct consequence of the stability of the CH₄ molecule. The incorporation of carbon during film growth most likely takes place via adsorbed CH₃ radicals, and their decomposition products, arising from the dissociation of TMG.     

Grain growth of copper films prepared by chemical vapour deposition

Copper films having thickness 600 nm were prepared on TiN using chemical vapour deposition (CVD). The deposited films were annealed at various temperatures (350–550°C) in Ar and H₂(10%)-Ar ambients. The changes in the grain size of the films upon annealing were investigated. Annealing in an H₂(10%)-Ar ambient produced normal grain growth; annealing in an Ar ambient caused grain growth to stop at 550°C. The grain size followed a monomodal distribution and the mean size increased in proportion to the square root of the annealing time, indicating the curvature of the grain is the main driving force for grain growth. Upon annealing at 450°C for 30 min in an H₂(10%)-Ar ambient, the average grain size of the film increased from 122 nm to 219 nm, and the resistivity decreased from 2.35 μΩ cm to 2.12 μΩ cm at a film thickness of 600 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modification of mordenite by chemical vapour deposition of metal chloride

Pore structure modification of a zeolite molecular sieve can be achieved by chemical vapour deposition (c.v.d.) of metal chlorides such as SiCl₄, GeCl₄ etc. followed by hydrolysis and calcination. Characterization has been done by t.p.d. of NH₃ to determine acid properties, by liquid phase adsorption of C₆H₁₄ isomers to examine the change in pore structure, and by fluorescent X-ray spectrometry to measure amount of deposition. Metal chloride deposits either along the interior channel or only near the channel entrance depending on its reactivity and molecular size, and on the deposition condition. Methanol conversion on these mordenites showed changes in selectivity and activity.     

Surface,structural and electrical properties of BaTiO3 films grown on p-Si substrates by low pressure metal organic chemical vapour deposition

Metal organic chemical vapour deposition of BaTiO₃ using Ba(tmhd)₂, Ti(OC₃H₇)₄ and N₂O, where tmhd equals 2,2,6,6-tetramethyl-3,5-heptanedionate, via pyrolysis at relatively low temperatures (370C) was performed in order to produce BaTiO₃ insulator gates. Scanning electron microscopy showed that the surfaces of the BaTiO₃ films had very smooth morphologies. Atomic force microscopy showed that the BaTiO₃ thin film was polycrystalline. X-ray diffraction results indicated that BaTiO₃ crystalline films grew on Si(100) with [110] orientation. High resolution transmission electron microscopy measurements showed that the BaTiO₃ films were polycrystalline, and an interfacial layer in the BaTiO₃/Si interface was formed. The stoichiometry and atomic structure of the BaTiO₃ films were investigated by Auger electron spectroscopy and transmission measurements, respectively. Room temperature capacitance-voltage measurements clearly revealed metal-insulator-semiconductor behaviour for samples with BaTiO₃ insulator gates, and interface state densities at the BaTiO₃/p-Si interface were approximately high, 10¹¹ eV^–1 cm^–2, at the middle of the Si energy gap.     

Diamond chemical vapour deposition on seeded cemented tungsten carbide substrates

Diamond particles were deposited onto seeded cemented tungsten carbide (WC-Co) substrates using conventional hot-filament chemical vapour deposition (HFCVD) and time-modulated CVD (TMCVD) processes. The substrates were pre-seeded ultrasonically with diamond particles of different grit sizes. In this investigation, we employ timed methane (CH₄) gas modulations, which are an integral part of our TMCVD process in order to enhance diamond nucleation density. During diamond deposition using the conventional HFCVD process, methane gas flow was maintained constant. The total hydrogen flow into the reactor during TMCVD process was higher than in the HFCVD process. Hydrogen etching can be expectedly more prominent in the TMCVD process than in HFCVD of diamond particles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that a proper selection of the diamond grit size for seeding using ultrasounds can lead to enhancement in the nucleation density values of about two orders of magnitude (10⁷ to 10⁹ cm^− 2). The TMCVD process using the different seeded substrates can result in high nucleation density values of up to 10¹⁰ cm^− 2.     

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O₂ flow rate of 7cm³ min^–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min^–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O₂ flow rate of 20–50 cm³ min^–1, high crystalline spinel-type Co₃O₄ films were formed at a substrate temperature of 150–400°C. The Co₃O₄ film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co₃O₄ films were 20–41 nm min^–1. Both Co₃O₄ films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co₃O₄ film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.