Existing inorganic materials for radiation dosimeters suffer from several drawbacks, including their inability to cover large curved areas, lack of tissueequivalence, toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triarylamine) (PTAA)-based devices have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. The device was prepared by sandwiching an active layer of PT AA between a transparent indium tin oxide (ITO) b()ttom contact and a metal top contact. The charge transport properties of the device were assessed using the spectral photo current method. Increased photocurrent sensitivity was observed for samples annealed at 150°C, consistent with solvent loss, which was confirmed by thermogravimetric analysis. A diode with an Al contact shows the highest quality of recti tying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo Ka X-radiation over long timescales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. To optimize the performance of the device, the X-ray stopping power and the charge carrier mobility of the active layer have been modified by the introduction of various concentrations of the high atomic number bismuth oxide nanoparticles and the high mobility TIPS-pentacene organic material, respectively. The increasing of the devices' sensitivity correlates with an increased charge carrier mobility which was measured by a time-of-flight photocurrent measurement. Good stability of Xray sensitivity was found as the dosimeter was exposed to the X-ray beam for a long period of time with no discernible reduction in performance. These results indicate that PTAA is a highly-promising material for the direct detection of X-rays and potentially other types of radiation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:538028 |
| Date | January 2011 |
| Creators | Intaniwet, Akarin |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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