Effects of different needles and substrates on CuInS2 deposited by electrostatic spray deposition

Copper indium disulphide (CuInS2) thin films were deposited using the electrostatic spray deposition method. The effects of applied voltage and solution flow rate on the aerosol cone shape, film composition, surface morphology and current conversion were investigated. The effect of aluminium substrates and transparent fluorine doped tin oxide (SnO2:F) coated glass substrates on the properties of as-deposited CuInS2 films were analysed. An oxidation process occurs during the deposition onto the metallic substrates which forms an insulating layer between the photoactive film and substrate. The effects of two different spray needles on the properties of the as-deposited films were also studied. The results reveal that the use of a stainless steel needle results in contamination of the film due to the transfer of metal impurities through the spray whilst this is not seen for the glass needle. The films were characterised using a number of different analytical techniques such as X-ray diffraction, scanning electron microscopy, Rutherford back-scattering and secondary ion mass spectroscopy and opto-electronic measurements

Thick film growth of high optical quality low loss (0.1dB/cm) Nd:Gd₃Ga₅O₁₂ on Y3Al5O12 by pulsed laser deposition

Thick film growth of high optical quality Nd:Gd3Ga5O12 (Nd:GGG) on Y3Al5O12 (YAG) is reported, using the pulsed laser deposition (PLD) technique. Nd:GGG films with thickness up to 135 µm have been grown via sequential deposition runs and up to 40 µm in a single deposition. X-ray diffraction analysis shows that epitaxial growth has occurred and also confirms that the thick Nd:GGG films are single crystal. Analysis by Rutherford backscattering spectrometry shows that the stoichiometry of the thick Nd:GGG films is close to that of bulk Nd:GGG. The thick Nd:GGG films have fluorescence and absorption properties similar to that of bulk Nd:GGG, but slightly broadened. The Findlay–Clay technique of loss calculation has yielded a value of 0.1 dB cm-1 as an estimate of the propagation loss of one of the thick Nd:GGG films that we have subsequently used as a laser medium

Potential contribution of selected metallic restorative dentistry materials to X-ray fluorescence

Recent advances have led to the use of new materials in dental restoration which is an area of rapid growth. Applications include improving oral aesthetics and essential rehabilitation, whilst procedures range from the recovery of partial elements (inlays) to fitting dental implants. Ceramics, polymers and metallic materials have all been successfully employed in dental applications and benefit from new cost efficient manufacturing techniques. The application of radiographic techniques in dentistry and other medicine is also increasing, and the combination of new materials and radiation can lead to an elevated health risk. X-rays can interact with metallic materials producing X-ray fluorescence, which can increase the radiation dose in proximity to restorative material and increase the risk of live biological tissue becoming cancerous. The issue demands consideration so that the biological risks associated with such procedures are kept as low as possible. Comparisons of doses calculated for several materials have provided evidence that the Ti cp and NiCrTi alloys present less contribution to the increase of dose in surrounding soft tissue and the potential deleterious biological effects. On the other hand, Amalgam appears to be the most deleterious alloy

Modelling oxide thin films

Three simulation methodologies have been employed to investigate the growth, nucleation, and structure of oxides supported on oxide substrates, these are atom-by-atom deposition, layer-by-layer deposition and finally amorphisation of a structure followed by recrystallisation. The materials which have been investigated include the rocksalt-structured oxides; MgO, CaO, SrO, and BaO, the perovskite structured SrTiO3 and also fluorite structured CeO2 and ZrO2. The work has shown that the substrate influences critically the structure of the supported thin film by determining the nature and interactions of defects, dislocations and grain-boundaries, as well as influencing the interfacial ion densities and various epitaxial relationships. In addition, graphical techniques have been employed to show the three-dimensional atomistic structure of each structural and epitaxial feature. Moreover, by considering large simulation cell sizes (approaching the mesoscale, 18 nm square), it has been possible to accommodate the synergistic interactions between neighbouring structural features, which can lead to changes in their basic structure. We also show that the particular surface termination of the substrate can influence the structure (and tentatively, the critical thickness) of the supported film through the example of SrO and TiO2 terminated faces of a SrTiO3(001) substrate. © 2002 Taylor & Francis Ltd

Atomistic simulation methodologies for modelling the nucleation, growth and structure of interfaces

There have been many studies applying atomistic simulation techniques to investigate the structure and energetics of surfaces and interfaces. Almost all start by defining the basic structure of the interface, which is then simulated by static or dynamical methods. A different approach is adopted here, where we allow interfacial structures to evolve during the course of the simulation. In particular, three atomistic simulation methodologies for constructing models for thin film interfaces have been developed, including 'atom deposition', where the thin film is 'grown' by sequentially depositing atoms onto a support material to obtain information on nucleation and growth mechanisms; 'layer-by-layer' growth, where monatomic layers of a material are successively deposited on top of a substrate surface; and finally, 'cube-on- cube' whereby the whole of the thin film is placed directly on top of the substrate, before dynamical simulation and energy minimisation. The methodologies developed in this study provide a basis for simulating the nucleation, growth and structure of interface systems ranging from small supported clusters to monolayer and multilayer thin film interfaces. In addition, the layer-by-layer methodology is ideally suited to explore the critical thickness of thin films. We illustrate these techniques with studies on systems with large negative misfits. The calculations suggest that the thin films (initially constrained under tension due to the misfit) relax back to their natural lattice parameter resulting in the formation of surface cracks and island formation. The cube-on-cube methodology was then applied to the SrO/MgO system, which has a large (+ 20%) positive misfit. For this system, the SrO thin film underwent an amorphous transition which, under prolonged dynamical simulation, recrystallised revealing misfit-induced structural modifications, including screw-edge dislocations and low angle lattice rotations