John Futter

UV and humidity sensing properties of ZnO nanorods prepared by the arc discharge method

The UV and humidity sensing properties of ZnO nanorods prepared by arc discharge have been studied. Scanning electron microscopy and photoluminescence spectroscopy were carried out to analyze the morphology and optical properties of the as-synthesized ZnO nanorods. Proton induced x-ray emission was used to probe the impurities in the ZnO nanorods. A large quantity of high purity ZnO nanorod structures were obtained with lengths of 0.5-1 microm. The diameters of the as-synthesized ZnO nanorods were found to be between 40 and 400 nm. The nanorods interlace with each other, forming 3D networks which make them suitable for sensing application. The addition of a polymeric film-forming agent (BASF LUVISKOL VA 64) improved the conductivity, as it facilitates the construction of conducting networks. Ultrasonication helped to separate the ZnO nanorods and disperse them evenly through the polymeric agent. Improved photoconductivity was measured for a ZnO nanorod sensor annealed in air at 200 degrees C for 30 min. The ZnO nanorod sensors showed a UV-sensitive photoconduction, where the photocurrent increased by nearly four orders of magnitude from 2.7 x 10(-10) to 1.0 x 10(-6) A at 18 V under 340 nm UV illumination. High humidity sensitivity and good stability were also measured. The resistance of the ZnO nanorod sensor decreased almost linearly with increasing relative humidity (RH). The resistance of the ZnO nanorods changed by approximately five orders of magnitude from 4.35 x 10(11) Omega in dry air (7% RH) to about 4.95 x 10(6) Omega in 95% RH air. It is experimentally demonstrated that ZnO nanorods obtained by the arc discharge method show excellent performance and promise for applications in both UV and humidity sensors.

Synthesis of Zinc Oxide Nanorods and their Sensing Properties

Zinc oxide (ZnO) nanorods have been synthesized via the arc discharge method. Different cathode materials, graphite and copper, were applied to modulate the morphology and UV & humidity sensing properties of the as-synthesized ZnO nanorods. Compared with ZnO nanorods synthesized by graphite cathode, shorter length and other spherical and cubical structures were also detected for those ZnO nanorods synthesized by copper cathode. A better UV-sensitive photoconduction and higher humidity sensitivity were detected for ZnO nanorods synthesized by graphite cathode than those obtained by copper cathode, which is considered to be due to the higher aspect ratio for long ZnO nanorods. The simplicity of the synthesis route coupled with the modulation of morphology and sensing properties of ZnO nanorods make the arc discharge method a very promising way to produce high quality ZnO nanorods with adjustable morphologies.

Transition metal ion implantation into diamond-like carbon coatings: development of a base material for gas sensing applications

Micrometre thick diamond-like carbon (DLC) coatings produced by direct ion deposition were implanted with 30 keV Ar+ and transition metal ions in the lower percentage (<10 at .%) range. Theoretical calculations showed that the ions are implanted just beneath the surface, which was confirmed with RBS measurements. Atomic force microscope scans revealed that the surface roughness increases when implanted with Ar+ and Cu+ ions, whereas a smoothing of the surface from 5.2 to 2.7 nm and a grain size reduction from 175 to 93 nm are measured for Ag+ implanted coatings with a fluence of 1.24 × 1016 at. cm-2. Calculated hydrogen and carbon depth profiles showed surprisingly significant changes in concentrations in the near-surface region of the DLC coatings, particularly when implanted with Ag+ ions. Hydrogen accumulates up to 32 at.% and the minimum of the carbon distribution is shifted towards the surface which may be the cause of the surface smoothing effect. The ion implantations caused an increase in electrical conductivity of the DLC coatings, which is important for the development of solid-state gas sensors based on DLC coatings.

Applications of nanoparticle-based fluxgate magnetometers for positioning and location

Magnetic sensors can provide a very useful alternative for indicating the position or location of a subject and in conditions where other technologies will fail. For instance, GPS cannot accurately be used indoor and accelerometer-based systems have not yet reached the accuracy required for location after traversing long distances. In this paper we present results from a preliminary investigation aimed at determining the potential of three axes fluxgate magnetometers for personal location. Fluxgate magnetometers can display high sensitivity to magnetic fields but are limited by the properties of the core material. We discuss the potential and advantages of nanoparticle fluxguides in fluxgate magnetometers for positioning and location applications. The nanoparticles used for this study were synthesised using an arc-discharge method.

A novel radial anode layer ion source for inner wall pipe coating and materials modification—Hydrogenated diamond-like carbon coatings from butane gas

We report a new ion source development for inner wall pipe coating and materials modification. The ion source deposits coatings simultaneously in a 360° radial geometry and can be used to coat inner walls of pipelines by simply moving the ion source in the pipe. Rotating parts are not required, making the source ideal for rough environments and minimizing maintenance and replacements of parts. First results are reported for diamond-like carbon (DLC) coatings on Si and stainless steel substrates deposited using a novel 360° ion source design. The ion source operates with permanent magnets and uses a single power supply for the anode voltage and ion acceleration up to 10 kV. Butane (C4H10) gas is used to coat the inner wall of pipes with smooth and homogeneous DLC coatings with thicknesses up to 5 μm in a short time using a deposition rate of 70 ± 10 nm min(-1). Rutherford backscattering spectrometry results showed that DLC coatings contain hydrogen up to 30 ± 3% indicating deposition of hydrogenated DLC (a-C:H) coatings. Coatings with good adhesion are achieved when using a multiple energy implantation regime. Raman spectroscopy results suggest slightly larger disordered DLC layers when using low ion energy, indicating higher sp(3) bonds in DLC coatings. The results show that commercially interesting coatings can be achieved in short time.

Transition metal doped metal oxide nanostructures synthesized by arc discharge method

Doping metal oxides with metallic impurities has been the subject of previous studies for enhanced sensing performance. In this paper, we present a review on syntheses of transition metal doped metal oxide nanostructures using arc discharge method. Tungsten oxide was doped with Palladium, Scandium and Vanadium, respectively. Nickel was chosen to dope Zinc oxide by arc discharge method. It is demonstrated that dopants not only change the morphology of metal oxide nanostructures but also help to achieve an improved electrical conductivity. Because it is easy to tailor the morphology by adjusting the arc discharge parameters and dopant can be prescribed in the preparation of the anode material, the arc discharge is considered to be a fast and inexpensive synthesis method for doping which can be used to produce high quality doped metal oxide nanostructures for chemical sensing measurements.