Papers by Michael Warwick
We report on the design of nanosystems based on functionalized-Fe 2 O 3 nanostructures supported ... more We report on the design of nanosystems based on functionalized-Fe 2 O 3 nanostructures supported on fluorine-doped tin oxide (FTO) substrates. The target materials were developed by means of hybrid vapor phase approaches, combining plasma assisted-chemical vapor deposi-tion (PA-CVD) for the production of iron(III) oxide systems and the subsequent radio frequency (RF)-sputtering or atomic layer deposition (ALD) for the functionalization with Au nanoparticles or TiO 2 overlayers, respectively. The interplay between material characteristics and the adopted processing parameters was investigated by complementary analytical techniques, encompassing X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), and energy dispersive X-ray spectroscopy (EDXS). The obtained results highlight the possibility of fabricating Au/-Fe 2 O 3 nanocomposites, with a controlled dispersion and distribution of metal particles, and TiO 2 /-Fe 2 O 3 heterostructures, characterized by an intimate coupling between the constituent oxides.
Chemical Vapor Deposition, Jun 1, 2012
Thin films of titanium dioxide are deposited on gas-sensor substrates at 450 8C from the aerosol-... more Thin films of titanium dioxide are deposited on gas-sensor substrates at 450 8C from the aerosol-assisted (AA)CVD of titanium isopropoxide solutions in toluene under the influence of electric fields. Electric fields are generated by applying a potential difference between the inter-digitated electrodes of the gas-sensor substrate during the deposition. The deposited films are analyzed and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). It is found that an increase in electric field strength during deposition causes changes in the film microstructure, preferential orientation, and growth rate. The gas-sensor properties of the films are also examined. It is found that applying an electric field during the deposition improves the film microstructure and leads to a two-fold enhancement in the sensing properties of the film.
Advanced Materials Interfaces, 2015
Surface Science Spectra, 2015
Schizophr Res, 2000
Positron emission tomography (PET) studies of people with schizophrenia, performing verbal fluenc... more Positron emission tomography (PET) studies of people with schizophrenia, performing verbal fluency, report a failure of normal 'deactivation' of left superior temporal gyms (STG) in the presence of activation of left dorsolateral prefrontal cortex (DLPFC). This deficit has been attributed to underlying 'functional dis-connectivity' between these regions. To test the hypotheses that failure of left STG 'deactivation' and frontotemporal dis-connectivity (in the context of verbal fluency) provide trait-markers for genetic risk of schizophrenia, we use H2150 PET to examine verbal fluency in 10 obligate carriers (OC's) of the predisposition to schizophrenia, 10 stable schizophrenic patients, and 10 normal controls. We found no evidence of a failure of left STG deactivation in either OC's or patients. Instead, patients failed to deactivate precuneus compared to both OC's and controls. Furthermore, we found no evidence of differences in functional connectivity between left DLPFC and left STG in any of the groups studied. However, people with schizophrenia exhibited significant dis-connectivity between left DLPFC and anterior cingulate cortex, relative to both other groups (all results at P < 0.05, corrected for multiple comparisons). Qualitatively aberrant (but statistically nonsignificant) patterns of bi-frontal activity were exhibited by patients and obligates. Failure of left STG 'deactivation' and left fronto-temporal dis-connectivity are not consistent findings in schizophrenia; nor are they trait-markers for genetic risk. Prefrontal functional disconnectivity, as demonstrated here, may characterise the schizophrenia phenotypes but requires independent replication.
CrystEngComm, 2015
nanocomposites are fabricated by an original vapor phase synthetic strategy, consisting of the in... more nanocomposites are fabricated by an original vapor phase synthetic strategy, consisting of the initial growth of Fe 2 O 3 nanosystems on fluorine-doped tin oxide substrates by plasma enhanced-chemical vapor deposition, followed by atomic layer deposition of TiO 2 overlayers with variable thickness, and final thermal treatment in air. A thorough characterization of the target systems is carried out by X-ray diffraction, atomic force microscopy, field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. High purity nanomaterials characterized by the co-presence of Fe 2 O 3 (hematite) and TiO 2 (anatase), with an intimate Fe 2 O 3 -TiO 2 contact, are successfully obtained. In addition, photocatalytic tests demonstrate that, whereas both single-phase oxides do not show appreciable activity, the composite systems are able to degrade methyl orange aqueous solutions under simulated solar light, and even visible light, with an efficiency directly dependent on TiO 2 overlayer thickness. This finding opens attractive perspectives for eventual applications in wastewater treatment.
Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics. This journal is ... more Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics. This journal is © the Owner Societies 2015 2 EXPERIMENTAL DETAILS Synthesis. Fe 2 O 3 deposits were fabricated by means of a custom-built PE-CVD apparatus equipped with a radio frequency (RF, ν = 13.56 MHz) generator. 1 The diameter of each electrode was 9 cm and the inter-electrode distance was fixed at 6 cm. Growth experiments were performed from Ar/O 2 plasmas for a total duration of 1 h, using a fixed RF-power of 10 W and a total pressure of 1.0 mbar. The iron precursor Fe(hfa) 2 TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine), synthesized according to a previously reported procedure, 2,3 was placed in an external vessel heated by an oil bath maintained at 65 °C and transported into the reaction chamber by means of electronic grade Ar (flow rate = 60 sccm). The temperature of precursor feeding lines was maintained at 140 °C in order to prevent detrimental condensation phenomena. Two further auxiliary gas-lines were used to introduce Ar (flow rate = 15 sccm) and electronic grade O 2 (flow rate = 20 sccm) directly into the reactor chamber. Basing on previous results, 4 Fe 2 O 3 growth was performed at 300 °C on FTO-coated glass slides (Aldrich, 735167-1EA, 7 Ω/sq; lateral dimensions = 2.0 cm 1.0 cm; FTO thickness 600 nm), mounted on the grounded electrode. Prior to deposition, the substrates were suitably cleaned by iterative dipping in acetone, sulphonic detergent, distilled water, and finally dried under an air flow.
J. Mater. Chem. A, 2014
Nanostructured thin films of vanadium oxides were deposited using electric field assisted chemica... more Nanostructured thin films of vanadium oxides were deposited using electric field assisted chemical vapour deposition. The films were characterised using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that the films had open and porous morphologies with extremely small (5 nm) surface features. The films were made into supercapacitor cells and tested using cyclic voltammetry. It was found that stable asymptotic values specific capacitance values as high as 3700 mF cm À2 could be obtained with good cycling behaviour. Electrodes synthesized in this way show promise for applications in fields such as supercapacitors.
physica status solidi (a), 2015
Nanostructured Fe 2 O 3 thin films were grown by plasma enhanced-chemical vapor deposition (PE-CV... more Nanostructured Fe 2 O 3 thin films were grown by plasma enhanced-chemical vapor deposition (PE-CVD) from Ar/O 2 plasmas for photoelectrochemical (PEC) water splitting applications. Iron oxide coatings were deposited on fluorinedoped tin oxide (FTO) substrates at 300 8C under optimized conditions, and subsequently annealed ex situ in air at 650 8C. Structural and compositional analyses confirmed the formation of pure a-Fe 2 O 3 (hematite), free from other crystalline iron oxide phases. Controlled variations of the deposition time enabled tuning of the thickness and nano-aggregate sizes in the resulting deposits and, correspondingly, their current-voltage characteristics. A maximum photocurrent density close to 1 mA cm À2 was achieved at 1.23 V versus the reversible hydrogen electrode (RHE), without the need of any oxygen evolution catalyst or over/underlayer. The present findings revealed the key role played by the engineering of Fe 2 O 3 -based nanomaterials, resulting ultimately in a lowered carrier diffusion length, and in an optimal diffusion of tin from FTO into thinner layers. These features offer an amenable opportunity for harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen in a carbonneutral fashion.
Surface Science Spectra, 2015
Solar Energy Materials and Solar Cells, 2015
ABSTRACT Glazing based on thermochromic thin films has been noted to potentially reduce the energ... more ABSTRACT Glazing based on thermochromic thin films has been noted to potentially reduce the energy demand in buildings by modulating the solar heat gain depending on the coating temperature. Such “intelligent” glazing has been researched for a number of years with little attention paid to the thermochromic transition details such as the transition width and transition gradient. In this study we use idealised thermochromic spectra and the programme Energy Plus to simulate the effect of simultaneous variations in thermochromic transition width and gradient on building energy demand in order to elucidate which parameters are the most important for optimal energy saving behaviour. The investigation takes place across warm, varied and cold climates and the results are compared against current industry standards. The results suggest that under ideal conditions energy savings of greater than 50% compared to standard double-glazing are obtainable in a hot climate where the thermochromic transition occurs at a low temperature with a narrow hysteresis and sharp gradient.
ACS applied materials & interfaces, Jan 8, 2015
Harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen is receiv... more Harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen is receiving increasing attention in the search of alternative energy resources. In this regard, hematite (α-Fe2O3) nanostructures with controlled nano-organization have been fabricated and investigated for use as anodes in photoelectrochemical (PEC) cells. The target systems have been grown on conductive substrates by plasma enhanced-chemical vapor deposition (PE-CVD) and subjected to eventual ex-situ annealing in air to further tailor their structure and properties. A detailed multi-technique approach has enabled to elucidate the interrelations between system characteristics and the generated photocurrent. The present α-Fe2O3 systems are characterized by a high purity and hierarchical morphologies consisting of nanopyramids/organized dendrites, offering a high contact area with the electrolyte. PEC data reveal a dramatic response enhancement upon thermal treatment, related to a more efficient e...
Solar Energy Materials and Solar Cells, 2015
In this work, Ga-doped ZnO (GZO) films were prepared using the sol-gel dip coating method and the... more In this work, Ga-doped ZnO (GZO) films were prepared using the sol-gel dip coating method and the effects of film thickness (230-480 nm), heating temperature (400-600°C) and atmosphere (air/argon) on the system structural and opto-electronic performances were investigated. The results show that highly c-axis oriented crystals could be easily formed in GZO coatings, which origins from a preferred nucleation and gets fully developed during the structure evolution. The increase of film thickness prolongs the sol-gel preheating process and promotes nucleation, resulting in a more crystalline film. Higher temperature annealing (600°C) in air could degrade the Ga doping efficiency and decrease the carrier concentration, but the enlarged grain size helps enhance the carrier mobility and improve the film conductivity. Under the modified annealing process in argon, favorable carrier density (3.376 Â 10 19 cm À 3 ) and mobility (15.74 cm 2 (V s) À 1 ) can be obtained at the same time, resulting a minimum film resistivity of 1.18 Â 10 À 2 Ω cm. The studied GZO coatings keep transparent in the visible and near infrared range, leading to high emissivity values (40.738). We firstly prove that the carrier concentration could play a more dominant role than its mobility in determining the thermal emittance performance of thin films.
Chemical Vapor Deposition, 2015
ABSTRACT Thin films of anatase titanium dioxide are deposited on fluorine-doped tin oxide (FTO) g... more ABSTRACT Thin films of anatase titanium dioxide are deposited on fluorine-doped tin oxide (FTO) glass substrates utilizing the electric field-assisted aerosol (EA)CVD reaction of titanium isopropoxide in toluene at 450 °C. The as-deposited films are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and UV-vis spectroscopy. The photoactivity and antibacterial activity of the films are also assessed. The characterization analysis reveals that the use of an electric field affects the film microstructure, its preferential orientation, and the functional properties. XRD of the anatase films reveals that the application of electric fields causes a change in the preferential orientation of the films from (101) to (004) or (211) planes, depending on the strength of the applied field during the deposition.
Solar Energy Materials and Solar Cells, 2013
Films of titanium oxynitride are assessed for their potential as energy saving coatings on window... more Films of titanium oxynitride are assessed for their potential as energy saving coatings on window glass. The coatings are deposited from the atmospheric pressure chemical vapour reaction of TiCl 4 and ammonia. Film microstructure and composition was analysed using scanning electron microscopy, X-ray diffraction, pulsed RF GD OES and X-ray photoelectron spectroscopy. Transmission and reflectance spectroscopy were used to investigate the optical properties of the films.
Journal of Materials Chemistry a, 2013
ABSTRACT Nanostructured thin films of tungsten trioxide were deposited on to gas sensor substrate... more ABSTRACT Nanostructured thin films of tungsten trioxide were deposited on to gas sensor substrates at 600 °C from the aerosol assisted chemical vapour deposition reaction of tungsten hexaphenoxide solutions in toluene under the influence of electric fields. The electric fields were generated by applying a potential difference between the inter-digitated electrodes of the gas sensor substrates during the deposition. The deposited films were characterised using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The application of an electric field, encouraged formation of enhanced nanostructured morphologies, with an increase in needle length and reduction in needle diameter being observed. The film gas sensor properties were also examined; it was found that the highest response of 110 to 800 ppb NO2 was given by a sensor grown under the influence of a 1.8 × 104 V m−1 electric field and operated at 250 °C, a 2.5 times enhancement compared to a sensor grown in the absence of an electric field under its optimal operating conditions.
Journal of Materials Chemistry a, 2014
Open Journal of Energy Efficiency, 2013
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Papers by Michael Warwick