Browsing by Author "Roncallo, S."

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    ItemOpen Access
    An approach to high-throughput X-ray diffraction analysis of combinatorial polycrystalline thin film libraries
    (Blackwell Publishing Ltd, 2009-04-30T00:00:00Z) Roncallo, S.; Karimi, O.; Rogers, Keith; Lane, David W.; Ansari, S. A.
    With the demand for higher rates of discovery in the materials field, characterization techniques that are capable of rapidly and reliably surveying the characteristics of large numbers of samples are essential. A chemical combinatorial approach using thin films can provide detailed phase diagrams without the need to produce multiple, individual samples. This is achieved with compositional gradients forming high-density libraries. Conventional raster scanning of chemical or structural probes is subsequently used to interrogate the libraries. A new, alternative approach to raster scanning is introduced to provide a method of high-throughput data collection and analysis using an X-ray diffraction probe. Libraries are interrogated with an extended X-ray source and the scattering data collected using an area detector. A simple technique of 'partitioning' this scattering distribution enables determination of information comparable to conventional raster scanned results but in a dramatically reduced collection time. The technique has been tested using synthetic X-ray scattering distributions and those obtained from contrived samples. In all cases, the partitioning algorithm is shown to be robust and to provide reliable data; discrimination along the library principal axis is shown to be similar to 500 mm and the lattice parameter resolution to be similar to 10(-3) A angstrom mm(-1). The limitations of the technique are discussed and future potential applications described.
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    ItemOpen Access
    A study of electrostatically sprayed CuInS2 and ZnS thin films
    (2009-01-23T15:56:26Z) Roncallo, S.; Painter, J. D.
    The investigation of ternary compounds for the fabrication of thin film solar cells is well documented but the production of thin films by electrostatic spray deposition (ESD) is still limited. This thesis represents the first attempt to deposit photovoltaic thin films using this novel method. The lack of information regarding the deposition of CuInS2 by ESD required a statistical investigation of the effects of different deposition variables. To achieve this, a new image analysis method was developed to calculate the variation of the thickness of the as-deposited films using their optical density. The thickness variation across the sample was then used to define its uniformity. Once the conditions for the best uniformity were defined, different needle and substrate materials were investigated to try and improve the performance of the ESD method for potential large scale production. A formation of precipitates was observed during the preparation of the chloride precursor solutions (prepared from CuCl2, InCl3 and thiourea salts). A possible reaction mechanism was proposed and the chemical composition of precipitates analysed. An explanation of the absence of the precipitate during the preparation of a nitrate starting solution (from Cu(NO3)2, In(NO3)3 and thiourea salts) was reported. The behaviour of the aerosol cone for the two different starting solutions (nitrate and chloride) was established using the laser-based particle image velocimetry (PIV) measurement technique. The properties of as-deposited films sprayed by the two precursor solutions were thoroughly investigated using a number of techniques including X-ray diffraction (XRD), Rutherford backscattering (RBS), optoelectronic characterisation and miniSIMS. The effect of different precursor molar ratios on the properties of as-deposited films was studied for both the nitrate and chloride based solutions using the above techniques. ZnS films were also deposited using ESD for the first time. Using the information acquired during the deposition of the CuInS2, a fully comprehensive analysis of the effect of different deposition conditions and starting solution properties was performed. Finally, CdS/CuInS2 and ZnS/CuInS2 junctions were prepared and tested using EQE measurements in solution. Substrate and superstrate device configurations were used to prepare complete solar cells which were analysed using IV measurements.
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    ItemOpen Access
    Use of combinatorial analysis for the study of new material for solar cells applications
    (2009-11-11T00:00:00Z) Roncallo, S.; Karmimi, O.; Scragg, J. J.; Lane, David W.; Painter, J. D.
    This paper presents a combinatorial method for the deposition and characterization of new metallic precursors for photovoltaic materials. Onedimensional thin film alloy “libraries” were electrodeposited on Mo-coated glass. The library elements were deposited in two consecutive baths and then heated in a reducing atmosphere to promote interdiffusion of the elements. At the end of this process, the libraries possessed a composition gradient along their lengths, with single elements at their two opposite ends and one or more alloys and/or a solid state solution in between. This continuous range of compositions can therefore be considered a collection of specific precursors that can be interrogated by examining their corresponding locations, with the crystallographic structure along the library changing in accordance with the phase diagram for the metals. The libraries were then sulphurised or selenised by heating in a sulphur-rich or selenium rich atmosphere; this converted the metallic precursors in a continuous range of materials, candidates for potential solar cells absorbers. The libraries were analysed by X-ray diffraction and energy dispersive X-ray spectrometry. The X-ray diffraction results show phase changes across the libraries, which can be correlated with the original precursor concentration at that particular po