My research is centred on the use of Chemical Vapour Deposition (CVD) to deposit thin films of functional materials.
This has included the use of atmospheric variants to deposit thin films of various metal phosphides, oxides and selenides, the use of aerosol assisted CVD for the deposition of various nanostructured oxide materials and also the use of low pressure techniques for deposition of thin films of zirconium and tungsten carbonitrides. Principally my recent work has focussed on transparent conducting oxides, due to the unusual co-existence of optical transparancy AND electrical conductivity found in these materials, which is combined with chemical reactivity at the surface whilst the materials themselves are also relatively robust. The applications I have been targeting range from microelectronics to energy (active solar control coatings for energy demand reduction and catalysts for generation of hydrogen from water) through to the environment (gas sensing).
I am currently investigating the opportunities afforded by AACVD to synthesise materials with high purity and precise structural control at the nanometre scale level at the relatively low processing temperatures required for the fabrication of nanocrystalline materials. By altering the deposition conditions to control the chemical reaction it is possible to obtain nanocrystalline powders, nanostructured materials or thin films. Hence AACVD is a technique with great promise for synthesis of functional nanomaterials.
My most recent research is concerned with the use of AACVD for the synthesis of metal nanoparticle modified metal oxide nanostructures, with the aim of producing highly sensitive and highly selective gas sensors. This work, which is supported by the Leverhulme Trust, has recently been featured in an Emerging Investigators issue of Chemical Communications.
Methods of nanoparticle synthesis must be developed in accordance with green chemistry, but these techniques must also be compatible with device manufacture to ensure that green principles are followed throughout the fabrication process and also to ensure the potential benefits of the materials are realised. New manufacturing strategies that are additive rather than subtractive, i.e. bottom-up synthesis strategies, can reduce energy requirements and waste generation. A potentially greener approach to top-down or wet-chemical methods of nanoparticle synthesis is to employ direct deposition from the vapour phase, which provides increased atom efficiency and reduced waste production. Hence I am currently investigating the potential of AACVD for use in 'green nanotechnology'.
1) S. Vallejos, T. Stoycheva, P. Umek, C. Navio, R. Snyders, C. Bittencourt, E. Llobet, C. Blackman, S. Moniz, X. Correig
Au-nanoparticle functionalised WO3 nanoneedles and their application in high sensitivity gas sensor devices
Chem. Commun., 2011, 47, 565
This article was an invited contribution to a special 'Emerging Investigators' issue of Chemical Communications and this article is currently available free of charge.
A new method of synthesising nanoparticle-functionalised nanostructured materials via Aerosol Assisted Chemical Vapour Deposition (AACVD) has been developed. Co-deposition of Au nanoparticles with WO3 nanoneedles has been used to deposit a sensing layer directly onto gas sensor substrates providing devices with a six-fold increase in response to low concentrations of a test analyte (ethanol).
2) S.J.A. Moniz, C.S. Blackman, C.J. Carmalt, G. Hyett
MOCVD of crystalline Bi2O3 thin films using a single-source bismuth alkoxide precursor and their use in photodegradation of water
J. Mater. Chem., 2010, 20, 7881
Bismuth(III) tert-butoxide [Bi(OtBu)3] was utilised as a single-source precursor to controllably deposit thin films of different phases of bismuth oxide (Bi2O3) on glass substrates via low-pressure chemical vapour deposition (LPCVD). Band gaps for the different phases have been measured (Eg = 2.3–3.0 eV) and the films displayed excellent photodegradation of water under near-UV irradiation.
3) S. Ashraf, C.S. Blackman, S. Naisbitt, R.G. Palgrave, I.P. Parkin
Aerosol assisted chemical vapour deposition of WO3 thin films from tungsten hexacarbonyl and their gas sensing properties
J. Mater. Chem., 2007, 17, 3708
Aerosol assisted chemical vapour deposition (AACVD) reactions of tungsten hexacarbonyl, [W(CO)6], in acetone, methanol, acetonitrile and a 50 : 50 mixture of acetone and toluene resulted in the deposition of blue partially reduced WO3−xfilms which showed preferred orientation along the (0 1 0) direction. The WO3films functioned as gas sensitive resistors for the detection of NO2. Responses were recorded at minimum concentrations of 1.03 ppm of NO2, significantly exceeding those of commercial screen printed sensors.
4) S. Ashraf, C.S. Blackman, I.P. Parkin
Aerosol assisted chemical vapour deposition of tungsten oxide thin films on glass from polyoxometallate precursors and their gas-sensing properties
J. Mater. Chem., 2007, 17, 1063
Aerosol-assisted chemical vapour deposition (AACVD) of polytungstates in acetonitrile or water yielded thin films of tungsten oxide on glass. The WO3 films functioned as gas sensors showing a linear change in electrical resistance upon exposure to trace amounts of ethanol and nitrogen dioxide vapour in air, with responses comparable to that of screen-printed sensors and a faster speed of response.