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

Al-, Ga-, and In-doped ZnO thin films via aerosol assisted CVD for use as transparent conducting oxides

Al-, Ga-, and In-doped ZnO thin films were deposited on glass substrates by aerosol assisted chemical vapour deposition (AACVD) at a deposition temperature of 450 °C. The air-stable compound zinc acetylacetonate [Zn(acac)2] was used as a Zn source, whilst for the dopants of Al, Ga and In, the corresponding trichloride was used. Methanol solutions of the metal salts were used as precursor solutions and N2 carrier gas was used for the aerosol. Films were grown in approximately 30 min and were synthesised using dopant values of 5, 10, 15 and 20 mol.% (with respect to the Zn) in the precursor solution. XRD analysis showed that the films were wurtzite ZnO. XPS analysis confirmed the presence of the dopants in the films. Several of the films showed high transparency (>80%) in the visible range, and low resistivity (∼10−3 Ω cm)

Fiber-optic Ultrasound Transducers with Carbon/PDMS Composite Coatings

Novel ultrasound transducers were created with a composite of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) that was dip coated onto the end faces of optical fibers. The CNTs were functionalized with oleylamine to allow for their dissolution in xylene, a solvent of PDMS. Ultrasound pulses were generated by illuminating the composite coating with pulsed laser light. At distances of 2 to 16 mm from the end faces, ultrasound pressures ranged from 0.81 to 0.07 MPa and from 0.27 to 0.03 MPa with 105 and 200 μm core fibers, respectively. Using an optical fiber hydrophone positioned adjacent to the coated 200 µm core optical fiber, ultrasound reflectance measurements were obtained from the outer surface of a sheep heart ventricle. The results of this study suggest that ultrasound transducers that comprise optical fibers with CNT-PDMS composite coatings may be suitable for miniature medical imaging probes

Electronic properties of antimony-doped anatase TiO2 thin films prepared by aerosol assisted chemical vapour deposition

The electronic properties of antimony-doped anatase (TiO2) thin films deposited via aerosol assisted chemical vapour deposition were investigated by a range of spectroscopic techniques. The incorporation of Sb(V) into the TiO2 lattice was characterised by X-ray absorption spectroscopy and resulted in n-type conductivity, with a decrease in sheet resistance by four-orders of magnitude compared to that of undoped TiO2 films. The films with the best electrical properties displayed charge carrier concentrations of ca. 1 × 1020 cm−3 and a specific resistivity as low as 6 × 10−2 Ω cm. Doping also resulted in an orange colouration of the films that became progressively stronger with increasing Sb content. X-ray photoelectron spectroscopy showed that substantial segregation of Sb(III) to the surface of the film was associated with the appearance of lone pair surface states lying above the top of the main O 2p valence band. The pronounced visible region absorption in the films is attributed to transitions from the Sb(III) states at surface and grain boundary interfaces into the conduction band. The segregation of Sb leads to p-type surface layers at high doping levels and limits the mobility in this new conducting oxide

Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity

We report the synthesis and photoelectrochemical assessment of phase pure tetragonal matlockite structured BiOX (where X = Cl, Br, I) films. The materials were deposited using aerosol-assisted chemical vapour deposition. The measured optical bandgaps of the oxyhalides, supported by density functional theory calculations, showed a red shift with the increasing size of halide following the binding energy of the anion p-orbitals that form the valence band. Stability and photoelectrochemical studies carried out without a sacrificial electron donor showed the n-type BiOBr film to have the highest photocurrent reported for BiOBr in the literature to date (0.3 mA cm−2 at 1.23 V vs. RHE), indicating it is an excellent candidate for solar fuel production with a very low onset potential of 0.2 V vs. RHE. The high performance was attributed to the preferred growth of the film in the [011] direction, as shown by X-ray diffraction, leading to internal electric fields that minimize charge carrier recombination

Single Step Solution Processed GaAs Thin Films from GaMe 3 and BuAsH 2 under Ambient Pressure

This article reports on the possibility of low-cost GaAs formed under ambient pressure via a single step solution processed route from only readily available precursors, tBuAsH2 and GaMe3. The thin films of GaAs on glass substrates were found to have good crystallinity with crystallites as large as 150 nm and low contamination with experimental results matching well with theoretical density of states calculations. These results open up a route to efficient and cost-effective scale up of GaAs thin films with high material properties for widespread industrial use. Confirmation of film quality was determined using XRD, Raman, EDX mapping, SEM, HRTEM, XPS, and SIMS

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 cm(3)/V.s) and concentration (×10(19) cm(-3)). XPS indicated the presence of both W(6+) and W(4+) in the TiO2 matrix, with the substitutional doping of W(4+) 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

Electronic properties of antimony-doped anatase TiO2 thin films prepared by aerosol assisted chemical vapour deposition

The electronic properties of antimony-doped anatase (TiO2) thin films deposited via aerosol assisted chemical vapour deposition were investigated by a range of spectroscopic techniques. The incorporation of Sb(V) into the TiO2 lattice was characterised by X-ray absorption spectroscopy and resulted in n-type conductivity, with a decrease in sheet resistance by four-orders of magnitude compared to that of undoped TiO2 films. The films with the best electrical properties displayed charge carrier concentrations of ca. 1 × 1020 cm−3 and a specific resistivity as low as 6 × 10−2 Ω cm. Doping also resulted in an orange colouration of the films that became progressively stronger with increasing Sb content. X-ray photoelectron spectroscopy showed that substantial segregation of Sb(III) to the surface of the film was associated with the appearance of lone pair surface states lying above the top of the main O 2p valence band. The pronounced visible region absorption in the films is attributed to transitions from the Sb(III) states at surface and grain boundary interfaces into the conduction band. The segregation of Sb leads to p-type surface layers at high doping levels and limits the mobility in this new conducting oxide

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