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1	Nanostructured Metal Electrodes for Wool Processing and Electroanalysis Cruickshank, Amy Clare January 2007 (has links) The research presented in this thesis firstly concerns the use of electrochemical techniques to develop approaches to wool processing which have a lower impact on the environment than conventional chemical methods. Wool is a sulfur rich substrate and current methods used in wool processing often rely on sulfur-based reducing agents such as metabisulfite. However, due to increasing concern over the environmental impacts of metabisulfite, alternative methods are of interest. Electrochemical techniques have been applied to the process of wool setting in the presence of thiol setting agents. Wool disulfide bonds are reduced during this process and the thiol setting agent is converted to the disulfide. Efficient conversion of the disulfide back to the thiol setting agent would allow catalytic amounts of thiols to be used in wool setting. The electroreduction of cystine and 2-hydroxyethyl disulfide has been examined at a range of metal and carbon electrodes to find efficient methods of generating the corresponding thiols, cysteine and 2-mercaptoethanol respectively. Gold and silver were identified as the most efficient electrode materials. In industrial wool processing, the use of large-scale metal electrodes is expensive and therefore, high surface area gold and silver nanoparticle electrodes were fabricated by electrochemically depositing the metals onto low-cost carbon substrates. The most efficient electrochemical system for generating the thiol setting agent involved the electroreduction of cystine at the gold nanoparticle electrode and this system was used to successfully demonstrate that wool setting can be achieved using relatively low concentrations of cysteine. Further research was carried out to investigate methods for the controlled preparation of metal nanoparticle electrodes and their utility for detecting hydrogen peroxide was examined. A simple and versatile approach for the preparation of tethered gold nanoparticle assemblies was developed by exploiting electrostatic interactions between citrate-capped gold nanoparticles and amine tether layers attached to carbon surfaces. The nanoparticle assemblies were optimised for the detection of hydrogen peroxide by selecting the size and density of electrostatically assembled nanoparticles. The number of amine functionalities on the surface and the assembly conditions controlled the nanoparticle density. Nanostructured palladium electrodes fabricated using vapour deposition methods to immobilise palladium nanoparticles directly onto carbon substrates were also examined for the electroanalysis of hydrogen peroxide. electrochemistry nanostructured metal electrodes metal nanoparticles disulfide reduction electroanalysis of hydrogen peroxide
2	Electrical properties of amorphous selenium based photoconductive devices for application in x-ray image detectors Belev, Gueorgui Stoev 14 February 2007 In the last 10-15 years there has been a renewed interest in amorphous Se (a-Se) and its alloys due to their application as photoconductor materials in the new fully digital direct conversion flat panel x-ray medical image detectors. For a number of reasons, the a-Se photoconductor layer in such x-ray detectors has to be operated at very high electric fields (up to 10 Volts per micron) and one of the most difficult problems related to such applications of a Se is the problem of the dark current (the current in the absence of any radiation) minimization in the photoconductor layer. <p>This PhD work has been devoted to researching the possibilities for dark current minimization in a-Se x-ray photoconductors devices through a systematic study of the charge transport (carrier mobility and carrier lifetimes) and dark currents in single and multilayered a-Se devices as a function of alloying, doping, deposition condition and other fabrication factors. The results of the studies are extensively discussed in the thesis. We have proposed a new technological method for dark current reduction in single and multilayered a-Se based photoconductor for x-ray detector applications. The new technology is based on original experimental findings which demonstrate that both hole transport and the dark currents in a-Se films are a very strong function of the substrate temperature (Tsubstrate) during the film deposition process. We have shown that the new technique reduces the dark currents to approximately the same levels as achievable with the previously existing methods for dark current reduction. However, the new method is simpler to implement, and offers some potential advantages, especially in cases when a very high image resolution (20 cycles/mm) and/or fast pixel readout (more than 30 times per second) are needed. <p>Using the new technology we have fabricated simple single and double (ni-like) photoconductor layers on prototype x-ray image detectors with CCD (Charge Coupled Device) readout circuits. Dark currents in the a-Se photoconductor layer were not a problem for detector operation at all tested electric fields. Compared to the currently available commercial systems for mammography, the prototype detectors have demonstrated an excellent imaging performance, in particular superior spatial resolution (20 cycles/mm). Thus, the newly proposed technology for dark current reduction has shown a potential for commercialization. amorphous state amorphous semiconductors photoconductivity a Se photoconductors medical imaging radiation detectors high resolution digital mammography thick films experimental study electron hole pair lifetime localized states carrier lifetime trapping drift mobility carrier mobility charge carrier trapping alloying fabrication property relation arsenic additions doping chlorine additions deposition rate deposition conditions boat temperature substrate temperature annealing time-of-flight method dark current metal electrodes blocking layers double layer structure
3	Electrical properties of amorphous selenium based photoconductive devices for application in x-ray image detectors Belev, Gueorgui Stoev 14 February 2007 (has links) In the last 10-15 years there has been a renewed interest in amorphous Se (a-Se) and its alloys due to their application as photoconductor materials in the new fully digital direct conversion flat panel x-ray medical image detectors. For a number of reasons, the a-Se photoconductor layer in such x-ray detectors has to be operated at very high electric fields (up to 10 Volts per micron) and one of the most difficult problems related to such applications of a Se is the problem of the dark current (the current in the absence of any radiation) minimization in the photoconductor layer. <p>This PhD work has been devoted to researching the possibilities for dark current minimization in a-Se x-ray photoconductors devices through a systematic study of the charge transport (carrier mobility and carrier lifetimes) and dark currents in single and multilayered a-Se devices as a function of alloying, doping, deposition condition and other fabrication factors. The results of the studies are extensively discussed in the thesis. We have proposed a new technological method for dark current reduction in single and multilayered a-Se based photoconductor for x-ray detector applications. The new technology is based on original experimental findings which demonstrate that both hole transport and the dark currents in a-Se films are a very strong function of the substrate temperature (Tsubstrate) during the film deposition process. We have shown that the new technique reduces the dark currents to approximately the same levels as achievable with the previously existing methods for dark current reduction. However, the new method is simpler to implement, and offers some potential advantages, especially in cases when a very high image resolution (20 cycles/mm) and/or fast pixel readout (more than 30 times per second) are needed. <p>Using the new technology we have fabricated simple single and double (ni-like) photoconductor layers on prototype x-ray image detectors with CCD (Charge Coupled Device) readout circuits. Dark currents in the a-Se photoconductor layer were not a problem for detector operation at all tested electric fields. Compared to the currently available commercial systems for mammography, the prototype detectors have demonstrated an excellent imaging performance, in particular superior spatial resolution (20 cycles/mm). Thus, the newly proposed technology for dark current reduction has shown a potential for commercialization. amorphous state amorphous semiconductors photoconductivity a Se photoconductors medical imaging radiation detectors high resolution digital mammography thick films experimental study electron hole pair lifetime localized states carrier lifetime trapping drift mobility carrier mobility charge carrier trapping alloying fabrication property relation arsenic additions doping chlorine additions deposition rate deposition conditions boat temperature substrate temperature annealing time-of-flight method dark current metal electrodes blocking layers double layer structure

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