title: Achieving a stable time response in polymeric radiation sensors under charge injection by X-rays.
abstract: Existing inorganic materials for radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, lack of tissue-equivalence, toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triarylamine) (PTAA) diodes have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. A single layer of PTAA is deposited on indium tin oxide (ITO) substrates, with top electrodes selected from Al, Au, Ni, and Pd. The choice of metal electrode has a pronounced effect on the performance of the device; there is a direct correlation between the diode rectification factor and the metal-PTAA barrier height. A diode with an Al contact shows the highest quality of rectifying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo Kalpha X-radiation over long time scales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. Diodes with a low band gap, 'Ohmic' contact, such as ITO/PTAA/Au, show a slow transient response. This result can be explained by the build-up of space charge at the metal-PTAA interface, caused by a high level of charge injection due to X-ray-induced carriers. These data provide new insights into the optimum selection of metals for Schottky contacts on organic materials, with wider applications in light sensors and photovoltaic devices.
authors.affiliation: Department of Physics and Advanced Technology Institute, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom.
authors.forename: Akarin
authors.initials: A
authors.lastname: Intaniwet
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Mills
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Sellin
authors.forename: Maxim
authors.initials: M
authors.lastname: Shkunov
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Keddie
mesh_terms: D004307:Dose-Response Relationship, Radiation; D004566:Electrodes; D004581:Electronics; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D010777:Photochemistry / Q000379:methods; D011108:Polymers / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D017971:Tin Compounds / Q000737:chemistry; D014965:X-Rays
chemical_list: D011108:Polymers; D012997:Solvents; D017971:Tin Compounds; C109984:indium tin oxide