Electrical,morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells

Molybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in “substrate configuration” thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films.     

Systematic study of bimodal suspensions of latex nanoparticles using dynamic light scattering

Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (DLS). In principle, DLS is able to estimate the hydrodynamic particle diameter and its intensity-weighted distribution. However, the measured correlation function or power spectrum must be inverted to obtain this size distribution. The inversion is an ill-posed mathematical problem, and only under certain assumptions can the distribution be determined reliably. Suspensions containing bimodal (or multi-modal) particle size distributions are particularly challenging. This study reports on DLS measurements on a range of bimodal distributions of latex spheres with varying ratios of particle sizes. To determine the efficacy of different inversion techniques, the data has been analyzed both with the algorithms implemented in the DLS instrument’s proprietary analysis software and with other inversion routines based on simple analytical models of the particle size distribution. In addition, the results of the DLS analysis have been compared to scanning and transmission electron microscopy (SEM and TEM) measurements.     

The effect of polymer coatings on proton transverse relaxivities of aqueous suspensions of magnetic nanoparticles

Iron oxide magnetic nanoparticles are good candidates for magnetic resonance imaging (MRI) contrast agents due to their high magnetic susceptibilities. Here we investigate 19 polyether-coated magnetite nanoparticle systems comprising three series. All systems were synthesized from the same batch of magnetite nanoparticles. A different polyether was used for each series. Each series comprised systems with systematically varied polyether loadings per particle. A highly significant (p < 0.0001) linear correlation (r = 0.956) was found between the proton relaxivity and the intensity-weighted average diameter measured by dynamic light scattering in the 19 particle systems studied. The intensity-weighted average diameter measured by dynamic light scattering is sensitive to small number fractions of larger particles/aggregates. We conclude that the primary effect leading to differences in proton relaxivity between systems arises from the small degree of aggregation within the samples, which appears to be determined by the nature of the polymer and, for one system, the degree of polymer loading of the particles. For the polyether coatings used in this study, any changes in relaxivity from differences in water exclusion or diffusion rates caused by the polymer are minor in comparison with the changes in relaxivity resulting from variations in the degree of aggregation.     

Discrete Element Modeling (DEM) of the Vertically Vibrated Particle Bed

Discreet element modeling (DEM) is a computational tool used for detailed exploration of dynamic particle bed behaviors. One such application is the analysis of finely sized particle mixtures under the influence of external forces such as vertical vibration, which is difficult, if barely at all accessible for detailed experimental analysis. Here, we examined the differential density dynamic particle bed behaviors, by the application of a modified two dimensional DEM-fluid model that incorporates the gravity and fluid effects, to replicate some of the important experimental based observations of segregation, heaping, tilting, high density particles on top and bottom, and partition cell separation. The simulation results compared favorably with the reported literature on the density segregation attributes such as high density particles on top at vertical vibration frequency of 6.3 and 7 Hz with corresponding dimensionless acceleration magnitude of 1.6 and 2, convection currents at vertical vibration frequency of 30, 40, and 30 with corresponding dimensionless acceleration magnitude of 3.5, 4, and 3, layer separation at vertical vibration frequency of 7 Hz with corresponding dimensionless acceleration magnitude 2 and partition cell separation at vertical vibration frequency of 45 Hz and corresponding dimensionless acceleration magnitude of 2.25 for simulated glass and bronze particle mixture properties.     

In-situ burning of oil in coastal marshes. 2. Oil spill cleanup efficiency as a function of oil type, marsh type, and water depth

In-situ burning of spilled oil, which receives considerable attention in marine conditions, could be an effective way to cleanup wetland oil spills. An experimental in-situ burn was conducted to study the effects of oil type, marsh type, and water depth on oil chemistry and oil removal efficiency from the water surface and sediment. In-situ burning decreased the totaltargeted alkanes and total targeted polycyclic aromatic hydrocarbons (PAHs) in the burn residues as compared to the pre-burn diesel and crude oils. Removal was even more effective for short-chain alkanes and low ring-number PAHs. Removal efficiencies for alkanes and PAHs were >98% in terms of mass balance although concentrations of some long-chain alkanes and high ring-number PAHs increased in the burn residue as compared to the pre-burn oils. Thus, in-situ burning potentially prevents floating oil from drifting into and contaminating adjacent habitats and penetrating the sediment. In addition, in-situ burning significantly removed diesel oil that had penetrated the sediment for all water depths. Furthermore, in-situ burning at a water depth 2 cm below the soil surface significantly removed crude oil that had penetrated the sediment. As a result, in-situ burning may reduce the long-term impacts of oil on benthic organisms.     

Comparison of Northern Ireland radon maps based on indoor radon measurements and geology with maps derived by predictive modelling of airborne radiometric and ground permeability data

Publicly available information about radon potential in Northern Ireland is currently based on indoor radon results averaged over 1-km grid squares, an approach that does not take into account the geological origin of the radon. This study describes a spatially more accurate estimate of the radon potential of Northern Ireland using an integrated radon potential mapping method based on indoor radon measurements and geology that was originally developed for mapping radon potential in England and Wales. A refinement of this method was also investigated using linear regression analysis of a selection of relevant airborne and soil geochemical parameters from the Tellus Project. The most significant independent variables were found to be eU, a parameter derived from airborne gamma spectrometry measurements of radon decay products in the top layer of soil and exposed bedrock, and the permeability of the ground. The radon potential map generated from the Tellus data agrees in many respects with the map based on indoor radon data and geology but there are several areas where radon potential predicted from the airborne radiometric and permeability data is substantially lower. This under-prediction could be caused by the radon concentration being lower in the top 30 cm of the soil than at greater depth, because of the loss of radon from the surface rocks and soils to air.     

An apparatus for comparison of foaming properties of soaps and detergents

Summary 1. The measurement of the foaming properties of soaps and detergents is shown to be possible by comparing the relative stability of a foam by measuring the effect of an arbitrary standard destructive mechanism acting upon a volume of foam during production under standard conditions and protected from adventitious destructive forces. 2. A simple apparatus and procedure for carrying out foam tests has been described and the reproductibility of the test evaluated. 3. Previous studies of foam comparison have been reviewed and criticisms offered regarding the procedures and conceptions involved.     

Characterization of the Factors Influencing Retained Austenite Stability in Q&P Steels via In Situ EBSD

Metallurgical and Materials Transactions A - The current work studies the correlations between microstructure and retained austenite (RA) transformation, in a single-quenched and partitioned...     

Impact Sensitivity of γ-Irradiated HMX

Impact of thin layers of HMX at room temperature and near liquid nitrogen temperature were performed. Polycrystalline powders of HMX irradiated with 7.5 megarad in evacuated tubes at liquid nitrogen temperature showed significant enhanced sensitivity. With 10-megarad irradiations of HMX in evacuated tubes at liquid nitrogen temperature frequent spontaneous explosions in HMX have occurred. ESR measurements on impacted HMX and RDX powders at room temperature and near liquid nitrogen temperature at energies of less than 1 kg · m have not produced detectable mechanically generated free radicals. A significant increase in sensitivity of vacuum irradiated HMX was observed but efforts to correlate this with the dominant frozen-in NO₂ γ-radical concentration were unsuccessful. It is suggested that the NO₂ radical is a chain terminating radical in explosive systems.