Conventional X-ray CT is not usually sufficient to determine microscopic compositional distributions. A dataconstrained
microstructure modeling (DCM) methodology has been developed which uses multiple CT data sets
acquired with different X-ray spectra, and incorporates them as model constraints. The DCM approach has been applied
to predict the distributions of corrosion inhibitor and filler in a polymer matrix. The DCM-predicted compositional
microstructures have a reasonable agreement with EDX images taken on the sample surface.
A multi-layered surface acoustic wave (SAW) transducer employing an R.F. magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer, for low concentration nitrogen dioxide (NO2) gas sensing is presented. The layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The dominant mode of acoustic propagation in the sensor is a combination of mainly a shear and a longitudinal displacement types. Such a structure has the advantage of confining the acoustic wave energy to the surface of the device, which increases the sensitivity of the system. A frequency shift of 30 kHz is shown for a concentration of 500ppb of NO2 in synthetic air, highlighting the possibility of such a sensor being targeted towards the sub-ppb levels of NO2.
Silicon carbide based metal-oxide-semiconductor (MOS) devices are attractive for gas sensing in harsh, high temperature environments. We present a novel hydrocarbon gas sensor based on a catalytic Metal-Reactive Insulator-Silicon Carbide (MRISiC) device. This sensor has been employed as a Schottky diode. The sensor presented is capable of operating at temperatures around 600°C. It has been exposed to propene gas, which lowers the barrier height of the diode. The MRISiC devices are based on semiconducting Ga2O3 - ZnO thin films prepared by the sol-gel process. The thin films were deposited onto the SiC by the spin coating technique and a Pt layer was deposited on the top of the metal oxide layer forming the Schottky barrier. The sensors responses were stable and repeatable towards propene at operating temperatures between 300 and 600°C. In this paper the effect of biasing is investigated by analyzing the output voltage of the diodes when biased at constant currents of 2 and 8 mA.
Layered Surface Acoustic Wave (SAW) devices that allow the propagation of Love mode acoustic waves will be studied in this paper. In these devices, the substrate allows the propagation of Surface Skimming Bulks Waves (SSBWs). By depositing layers, that the speed of Shear Horizontal (SH) acoustic wave propagation is less than that of the substrate, the propagation mode transforms to Love mode. Love mode devices which will be studied in this paper, have SiO2 and ZnO acoustic guiding layers. As Love mode of propagation has no movement of particles component normal to the active sensor surface, they can be employed for the sensing applications in the liquid media.
MoO3-WO3 thin films have been fabricated via the sol-gel method. FESEM, TEM, RBS and SIMS analysis techniques have been employed to analyse the films and material properties for use as gas sensors to detect CO and NO2. FESEM shows the film made up of segregated molybdenum crystals. TEM highlights the nano-sized grains sructure and crystallinity. RBS analysis confirmed the films are stoichimetric and that the Mo component of the system decreases as the annealing temperature is increased. SIMS illustrates the interesting elemental depth profiles of the films. The films were exposed to CO and NO2. MoO3-WO3 shows better NO2 sensitivity and selectivity compared to its single metal oxide constituents.
Layered Surface Acoustic Wave (SAW)immunosensors based on a substrate crystal cut that allows the propagation of Surface Skimming Bulk Wave (SSBW)have been fabricated. SiO2 and ZnO films with different thicknesses deposited onto the substrate to form the SAW device. The layered SAW device developed is a gravimetric sensor.Upon exposures to solutions containing IgG, the operational frequency of the system incorporating the sensor changes. In this paper, the sensitivity of the SAW devices with different film thicknesses will be compared. Their response to the biochemical components will be investigated.