Davinder S. Bhachu

Tungsten Doped TiO2 with Enhanced Photocatalytic and Optoelectrical Properties via Aerosol Assisted Chemical Vapor Deposition.

Tungsten doped titanium dioxide films with both transparent conducting oxide (TCO) and photocatalytic properties were produced via aerosol-assisted chemical vapor deposition of titanium ethoxide and dopant concentrations of tungsten ethoxide at 500 °C from a toluene solution. The films were anatase TiO2, with good n-type electrical conductivities as determined via Hall effect measurements. The film doped with 2.25 at.% W showed the lowest resistivity at 0.034 Ω.cm and respectable charge carrier mobility (14.9 cm3/V.s) and concentration (×1019 cm−3). XPS indicated the presence of both W6+ and W4+ in the TiO2 matrix, with the substitutional doping of W4+ inducing an expansion of the anatase unit cell as determined by XRD. The films also showed good photocatalytic activity under UV-light illumination, with degradation of resazurin redox dye at a higher rate than with undoped TiO2.

Laser-generated ultrasound with optical fibres using functionalised carbon nanotube composite coatings

Optical ultrasound transducers were created by coating optical fibres with a composite of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS). Dissolution of CNTs in PDMS to create the composite was facilitated by functionalisation with oleylamine. Composite surfaces were applied to optical fibres using dip coating. Under pulsed laser excitation, ultrasound pressures of 3.6 MPa and 4.5 MPa at the coated end faces were achieved with optical fibre core diameters of 105 and 200 μm, respectively. The results indicate that CNT-PDMS composite coatings on optical fibres could be viable alternatives to electrical ultrasound transducers in miniature ultrasound imaging probes.

Scalable route to CH3NH3PbI3 perovskite thin films by aerosol assisted chemical vapour deposition

Methyl-ammonium lead iodide is the archetypal perovskite solar cell material. Phase pure, compositionally uniform methyl-ammonium lead iodide thin films on large glass substrates were deposited using ambient pressure aerosol assisted chemical vapour deposition. This opens up a route to efficient scale up of hybrid perovskite film growth towards industrial deployment.

Textured fluorine-doped tin dioxide films formed by chemical vapour deposition.

The use of an aerosol delivery system enabled fluorine-doped tin dioxide films to be formed from monobutyltin trichloride methanolic solutions at 350-550 °C with enhanced functional properties compared with commercial standards. It was noted that small aerosol droplets (0.3 μm) gave films with better figures of merit than larger aerosol droplets (45 μm) or use of a similar precursor set using atmospheric pressure chemical vapour deposition (CVD) conditions. Control over the surface texturing and physical properties of the thin films were investigated by variation in the deposition temperature and dopant concentration. Optimum deposition conditions for low-emissivity coatings were found to be at a substrate temperature of about 450 °C with a dopant concentration of 1.6 atm% (30 mol% F:Sn in solution), which resulted in films with a low visible light haze value (1.74%), a high charge-carrier mobility (25 cm(2) V s(-1)) and a high charge-carrier density (5.7×10(20) cm(-3)) resulting in a high transmittance across the visible (≈80%), a high reflectance in the IR (80% at 2500 nm) and plasma-edge onset at 1400 nm. Optimum deposition conditions for coatings with applications as top electrodes in thin film photovoltaics were found to be a substrate temperature of about 500 °C with a dopant concentration of 2.2 atm% (30 mol% F:Sn in solution), which resulted in films with a low sheet resistance (3 Ω sq(-1)), high charge-carrier density (6.4×10(20) cm(-3)), a plasma edge onset of 1440 nm and the films also showed pyramidal surface texturing on the micrometer scale which corresponded to a high visible light haze value (8%) for light scattering and trapping within thin film photovoltaic devices.

PbO-Modified TiO2 Thin Films: A Route to Visible Light Photocatalysts

PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface.

Aerosol assisted chemical vapor deposition of conductive and photocatalytically active tantalum doped titanium dioxide films

This paper shows the aerosol assisted chemical vapour deposition of transparent, blue coloured and conductive tantalum doped titanium dioxide films from the CVD reaction of Ti(OEt)4 and Ta(OEt)5. Hall effect measurements showed the doped films to have excellent n-type electrical conductivity showing, to the best of our knowledge, the lowest reported sheet resistance ever recorded for Ta-doped TiO2 of 14 Ω sq−1. The Ta 6 atom% doped TiO2 film also showed the best electrical results with a charge carrier concentration of 1.60 × 1021 cm−3 and mobility of 1.44 cm2 V−1 s−1 making it a suitable electrode in photovoltaic devices. The doped films were multifunctional, showing good photocatalytic activity under UV-light illumination. XPS and XRD studies gave strong evidence that the Ta was entering the TiO2 lattice as Ta5+ and that a reduction of some Ti4+ to Ti3+ was observed.

Atmospheric pressure chemical vapour deposition of boron doped titanium dioxide for photocatalytic water reduction and oxidation

Boron-doped titanium dioxide (B-TiO2) films were deposited by atmospheric pressure chemical vapour deposition of titanium(iv) chloride, ethyl acetate and tri-isopropyl borate on steel and fluorine-doped-tin oxide substrates at 500, 550 and 600 °C, respectively. The films were characterised using powder X-ray diffraction (PXRD), which showed anatase phase TiO2 at lower deposition temperatures (500 and 550 °C) and rutile at higher deposition temperatures (600 °C). X-ray photoelectron spectroscopy (XPS) showed a dopant level of 0.9 at% B in an O-substitutional position. The ability of the films to reduce water was tested in a sacrificial system using 365 nm UV light with an irradiance of 2 mW cm(-2). Hydrogen production rates of B-TiO2 at 24 μL cm(-2) h(-1) far exceeded undoped TiO2 at 2.6 μL cm(-2) h(-1). The B-TiO2 samples were also shown to be active for water oxidation in a sacrificial solution. Photocurrent density tests also revealed that B-doped samples performed better, with an earlier onset of photocurrent.

Influencing FTO thin film growth with thin seeding layers: a route to microstructural modification

We report on the seeded growth of fluorine doped tin oxide (FTO) polycrystalline transparent conducting oxide (TCO) thin films on float glass using a novel two-step chemical vapour deposition (CVD) method. Aerosol-assisted CVD (AACVD) was used to grow a seed layer to direct and promote full film growth via an atmospheric pressure CVD (APCVD) overlay. The method allowed for reproducible control over morphology and denser, rougher, higher-performing TCO at a relatively low growth temperature (500 °C). Growth promotion depended on seeding time with an optimal seeding time being present, below which morphology control and conformal coverage was unavailable. The film properties and functional characteristics were characterised by SEM, AFM, XRD, XPS, UV-Vis-Near IR transmittance-reflectance and Hall Effect probe measurements. Highly transparent and electrically conductive films, comparable to commercial materials and with high roughness and low transmission haze values indicate the process yields high quality films with a controllable morphology that can be tuned to desired application. The versatile method provides a route towards the morphological control of high-quality FTO thin films with high optical clarity and low-emissivity properties and can be readily extended to a variety of different substrates and metal oxide materials.

Superhydrophobic silica wool—a facile route to separating oil and hydrophobic solvents from water

Abstract Silica microfiber wool was systematically functionalized in order to provide an extremely water repellent and oleophilic material. This was carried out using a two-step functionalization that was shown to be a highly effective method for generating an intense water repulsion and attraction for oil. A demonstration of the silica wools application is shown through the highly efficient separation of oils and hydrophobic solvents from water. Water is confined to the extremities of the material, while oil is absorbed into the voids within the wool. The effect of surface functionalization is monitored though observing the interaction of the material with both oils and water, in addition to scanning electron microscope images, x-ray photoelectron spectroscopy and energy dispersive x-ray analysis. The material can be readily utilized in many applications, including the cleaning of oil spills and filtering during industrial processes, as well as further water purification tasks—while not suffering the losses of efficiency observed in current leading polymeric materials.

Zeolite films: a new synthetic approach

Dense, adhesive zeolitic films were made for the first time by combining chemical vapour deposition (CVD) and hydrothermal methods. This new method uses a CVD process to deposit dense amorphous silica or titanium doped silica films which are then converted to a crystalline nanoporous zeolite by a hydrothermal process using an organic structure directing agent. To demonstrate the capability of the method, silicalite-1 (S-1) and titanium silicalite-1 (TS-1) zeolites were prepared. Both X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the presence of crystalline zeolite films with well-defined morphology. Ti K-edge X-ray absorption spectroscopy (XAS) revealed the presence of the metal ions in the framework of the zeolitic matrix and in isolated, tetrahedral sites both in the amorphous and crystalline zeolite films. Both the pores and the titanium centres in the films were also shown to be accessible for molecules, by reacting with n-hexene and H2O2.