Browsing by Author "McCulloch, DG"

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    Engineering titanium and aluminum oxide composites using atomic layer deposition
    (AIP Publishing, 2011-12-23) Biluš Abaffy, N; McCulloch, DG; Partridge, JG; Evans, PJ; Triani, G
    Mixed metal oxides provide a convenient means to produce coatings with tailored physical properties. We investigate the possibility of synthesizing novel coatings of mixed titanium and aluminum oxide using atomic layer deposition (ALD). Results show that ALD films were prepared with compositions ranging between Al2O3 and TiO2 having refractive indices between 1.6 and 2.4 (at λ = 550 nm) at low temperature. The microstructure and bonding environment within the films was investigated using electron microscopy and x-ray absorption spectroscopy. The films were amorphous, and the Ti and Al atoms were mixed at the atomic scale. The electrical breakdown characteristics of the films were measured and showed that films with intermediate compositions had poor leakage current properties, believed to be caused by the presence of distorted bonding configurations. This study shows that ALD can be used to deposit high quality thin films with tailored optical properties, particularly suitable for applications in which complex topographies are required. © 2011 American Institute of Physics
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    Fabrication, structural characterization and testing of a nanostructured tin oxide gas sensor
    (Institute of Electrical and Electronics Engineers (IEEE), 2009-04-07) Partridge, JG; Field, MR; Sadek, AZ; Kalantar-Zadeh, K; Du Plessis, J; Taylor, MB; Atanacio, AJ; Prince, KE; McCulloch, DG
    A nanostructured SnO 2 conductometric gas sensor was produced from thermally evaporated Sn clusters using a thermal oxidation process. SnO 2 clusters were simultaneously formed in an identical process on a Si 3 N 4 membrane featuring an aperture created by a focused ion beam (FIB). Clusters attached to the vertical edges of the aperture were imaged using a transmission electron microscope. The original morphology of the Sn cluster film was largely preserved after the thermal oxidation process and the thermally oxidized clusters were found to be polycrystalline and rutile in structure. NO 2 gas sensing measurements were performed with the sensor operating at various temperatures between 25degC and 290degC. At an operating temperature of 210degC, the sensor demonstrated a normalized change in resistance of 3.1 upon exposure to 510 ppb of NO 2 gas. The minimum response and recovery times for this exposure were 45 s and 30 s at an operating temperature of 265degC. The performance of the SnO 2 sensor compared favorably with previously published results. Finally, secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to establish the levels of nitrogen present in the films following exposure to NO 2 gas. © Copyright 2009 IEEE
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    Synthesis and characterisation of titanium vanadium nitride thin films
    (Australian Institute of Physics, 2005-01-31) Taylor, MB; Davies, KE; Gan, BK; McKenzie, DR; Bilek, MMM; McCulloch, DG; Latella, BA; Wilksch, PA; McPherson, M; Van den Brink, RA
    Many transition metal nitrides form very hard and wear resistant thin film coatings. Alloying of transition metal nitrides creates the possibility of producing films with even higher hardness and wear resistance. In this paper we look at alloying TiN and VN utilising a dual source pulsed cathodic arc. TiN and VN both form face centred cubic structures, have similar lattice parameters and are completely miscible over the entire range in bulk form . Of interest is the correlation between intrinsic stress, indentation hardness, microstructure and optical properties of Ti(1-x)VxN films over a range of compositions from x = 0 to x = 1. Previous work by Knotek [using magnetron sputtering showed that thin films of Ti(1-x)VxN made using a metal target of 25 atomic percent V and 75 atomic percent Ti showed the best wear resistance in a pin-on-disc test and the highest Vickers microhardness. In this work we vary the ratio of pulses applied to each cathode in the dual source filtered cathodic arc system to change the composition of the resultant film in a controllable manner. In this way, the properties over a range of composition can be evaluated. In addition to hardness, this work will explore the variations in optical properties of the alloys. Nitrides frequently exhibit attractive colours; for instance, the colour of TiN thin films deposited by plasma immersion ion implantation has been found to vary widely with the conditions of deposition. However, little has been published on the optical properties of the Ti(1-x)VxN alloy.