David W. Sheel

Intelligent window coatings: atmospheric pressure chemical vapour deposition of vanadium oxides

Thin films of the vanadium oxides, V2O5, VO2, VOx (x = 2.00–2.50) and V6O13 were prepared on glass substrates by atmospheric pressure chemical vapour deposition (APCVD) of vanadium tetrachloride and water at 400–550 °C. The specific phase deposited was found to be dependent on the substrate temperature and the reagent concentrations. The films were characterised by Raman microscopy, X-ray diffraction (XRD), Rutherford backscattering (RBS), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDX), reflectance/transmittance and UV absorption spectroscopy. The VO2 films show by Raman microscopy and reflectance/transmittance spectroscopy, reversible switching behaviour at 68 °C associated with a phase change from monoclinic (MoO2 structure) to tetragonal (TiO2, rutile structure).

Photocatalytic antimicrobial activity of thin surface films of TiO2, CuO and TiO2/CuO dual layers on Escherichia coli and bacteriophage T4

TiO2-coated surfaces are increasingly studied for their ability to inactivate microorganisms. The activity of glass coated with thin films of TiO2, CuO and hybrid CuO/TiO2 prepared by atmospheric Chemical Vapour Deposition (Ap-CVD) and TiO2 prepared by a sol–gel process was investigated using the inactivation of bacteriophage T4 as a model for inactivation of viruses. The chemical oxidising activity was also determined by measuring stearic acid oxidation. The results showed that the rate of inactivation of bacteriophage T4 increased with increasing chemical oxidising activity with the maximum rate obtained on highly active sol–gel preparations. However, these were delicate and easily damaged unlike the Ap-CVD coatings. Inactivation rates were highest on CuO and CuO/TiO2 which had the lowest chemical oxidising activities. The inactivation of T4 was higher than that of Escherichia coli on low activity surfaces. The combination of photocatalysis and toxicity of copper acted synergistically to inactivate bacteriophage T4 and retained some self-cleaning activity. The presence of phosphate ions slowed inactivation but NaCl had no effect. The results show that TiO2/CuO coated surfaces are highly antiviral and may have applications in the food and healthcare industries.

Biocidal Silver and Silver/Titania Composite Films Grown by Chemical Vapour Deposition

This paper describes the growth and testing of highly active biocidal films based on photocatalytically active films of , grown by thermal CVD, functionally and structurally modified by deposition of nanostructured silver via a novel flame assisted combination CVD process. The resulting composite films are shown to be highly durable, highly photocatalytically active and are also shown to possess strong antibacterial behaviour. The deposition control, arising from the described approach, offers the potential to control the film nanostructure, which is proposed to be crucial in determining the photo and bioactivity of the combined film structure, and the transparency of the composite films. Furthermore, we show that the resultant films are active to a range of organisms, including Gram-negative and Gram-positive bacteria, and viruses. The very high-biocidal activity is above that expected from the concentrations of silver present, and this is discussed in terms of nanostructure of the titania/silver surface. These properties are especially significant when combined with the well-known durability of CVD deposited thin films, offering new opportunities for enhanced application in areas where biocidal surface functionality is sought.

Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits. Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities. In addition, plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment. Here, we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide (VO2) hybrids, exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots. Polarization- and wavelength-dependent pump–probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas. The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant, antenna-mediated local heating on a picosecond time scale. The hybrid, nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO2 film without antennas, enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range. The hybrid solution of antennas and VO2 provides a conceptual framework to merge the field localization and phase-transition response, enabling precise, nanoscale optical memory functionalities.

Atmospheric pressure pecvd coating and plasma chemical etching for continuous processing

Plasma processing at atmospheric pressure (APPlasmas) has attractions for both economic and technological reasons. Potential costs-saving factors are associated with online-processing capability and increase throughput due to high deposition rates. Capital cost savings for both equipment and line space (foot print), and relative ease of integration, are further benefits in comparison to low-pressure-technology approaches. Three types of APPlasmas are considered for coating: microwave chemical vapor deposition (CVD), dc ArcJet-CVD based on a linearly extended plasma source, and dielectric barrier glow discharge plasma CVD. Spectroscopic plasma characterization has shown that high fluxes of activated species are available in the plasma downstream region and can be used for deep fragmentation of even stable molecules. After precursor injection, a range of atomic and molecular intermediates, precursor fragments, and reaction products were identified leading to a conclusion that a complete conversion of the element-organic precursors into an inorganic materials take place. Alternatively, the dc ArcJet source is used for plasma chemical etching. All AP-plasma-enhanced chemical vapor deposition (PECVD), reactors are designed for continuous air-to-air processing on flat or slightly shaped substrates and allow deposition of nonoxide films. Reactor design is supported by fluid-dynamic modeling. Typical thin-film growth rates for PECVD are in the range of 5-100 nm/s (static) and up to 2 nm*m/s (dynamic). The rates for plasma chemical etching are typically ten times higher. Plasma activation substantially widens the range of potential applications, e.g., coating on steel, lightweight metals, preshaped glass, and plastics. Developments are underway to explore the use of the coating technologies in areas such as scratch-resistant coatings on metals, barrier layers, self-clean coatings, biocidal functional surfaces, and antireflective coatings. The coating materials range explored, so far, includes: silica, titania, carbon, silicon nitride/carbide, and metal oxides

Novel antibacterial silver-silica surface coatings prepared by chemical vapour deposition for infection control.

Environmental contamination plays an important role in the transmission of infections, especially healthcare‐associated infections. Disinfection transiently reduces contamination, but surfaces can rapidly become re‐contaminated. Antimicrobial surfaces may partially overcome that limitation. The antimicrobial activity of novel surface coatings containing silver and silica prepared using a flame‐assisted chemical vapour deposition method on both glass and ceramic tiles was investigated.

Surface modification of aramid fibers by atmospheric pressure plasma-enhanced vapor deposition

Recent research results have indicated positive influences of inter-yarn friction on ballistic performance of woven fabrics and panels made from such fibers. The current investigation explores the effect of coating by means of atmospheric pressure plasma-enhanced vapor deposition with organic chemical (CH3)2Cl2Si on the inter-yarn friction. The scanning electron microscopy observations indicated that as the treatment time increases, more particles have been deposited on the surface of the fibers. The Fourier transform infrared spectra supported the existence of Si-O-Si vibration, which can be attributed to the chemical deposition. Energy-dispersive X-ray analysis further supported the deposition of the chemical compound. Experiments were carried out to evaluate the coefficients of static and kinetic frictions between the yarns and the results showed that the inter-yarn coefficient of static friction was increased from 0.1617 to 0.2969 and that of the kinetic friction increased from 0.1554 to 0.2436, as the treatment time increased to 4 minutes. In addition, there is evidence that the mechanical properties of the treated yarns were not negatively affected by the treatment.

Photoactive Thin Silver Films by Atmospheric Pressure CVD

We report the visible and UV activity of thin silver films. The films are grown using a CVD process employing aqueous-based silver precursors, flame-assisted chemical vapour deposition. This approach overcomes many of the previously encountered limitations to silver deposition by employing an atmospheric pressure process, low-cost and low-toxicity precursors. The resultant films are assessed for activity using stearic acid destruction as a model compound. We also report on the addition of titania to these silver films to increase the potential functionality. This activity is also demonstrated, where the films appear largely transparent to the eye, further widening the potential application of this work. It is speculated that the nanoparticulate nature, of the CVD silver, is crucial in determining photoactivity.

Optimum performance solar cells using atmospheric pressure chemical vapour deposition deposited TCOs

High performance transparent conducting oxides (TCOs), have significance for optimising PV performance. We have developed an advanced atmospheric pressure chemical vapour deposition process, by applying fast experimentation and using a combinatorial chemistry approach to aid the studies. The deposited films were characterised for crystallinity, morphology (roughness), haze and resistivity to aid optimisation of material suitable for solar cells. Optical measurements on these samples showed low absorption losses, less than 1% around 500 nm for one pass, which is much lower than those of industrially available TCOs. Selected samples were then used in manufacture of single junction a-Si : H solar cells, which showed high initial solar energy conversion efficiencies up to 9.3% and high short circuit current densities of 15 mA/cm². Compared with (commercially available) TCO CVD coated glasses, these TCO coatings show excellent performance resulting in a high quantum efficiency yield for a-Si : H solar cells.

Time-Resolved In-Situ Spectroscopic Monitoring of the CVD of Tin Oxide onto a Glass Substrate

Near-infrared diode laser absorption spectroscopy has been demonstrated as an in-situ, non-invasive probe for use with a CVD reactor. The technique has been applied to the CVD of tin oxide onto a glass substrate, and by monitoring the evolution of methane in the reactor, it has been shown that the concentration of methane is correlated with the deposition rate of the tin oxide film. This illustrates the powerful possibilities for monitoring thin film production and properties, in-situ, during deposition.