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      X-ray-induced changes in optical properties of doped and undoped amorphous selenium

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      JUNG-THESIS-2018.pdf (2.305Mb)
      Date
      2018-03-16
      Author
      Jung, YeonHee 1988-
      Type
      Thesis
      Degree Level
      Masters
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      Abstract
      Amorphous selenium has been used as an important material for the flat-panel X-ray image detector. Its image quality is affected by a sensitivity which is reduced under high or long duration of X-ray exposure due to the generation of defects. Experiments were conducted to investigate the changes in optical properties of doped and undoped a-Se when the samples were exposed to two doses of X-rays, 900 Gy and 3200 Gy, at 30 and 70 kVp. The samples were: aSe, a-Se:0.5% As, a-Se:6%As, a-Se:6% As and a-Se:6% As: ppm of Cs. After the cessation of X-ray irradiation, the recovery of the optical properties towards pre-exposure equilibrium values was also investigated. In addition, the dependence of optical properties on the temperature, alloying and doping have been studied. The transmission spectra T(λ) of all films were scanned from 450 nm to 2000 nm, and the thickness d, wedge Δ d, absorption coefficient α(λ), optical band gaps EgT, EgU and refractive index n(λ) were extracted from Swanepoel method from T(λ). The result shows that optical properties were influenced by the absorption of X-rays, heat and doping. The change in n(λ) was related to densification by the Clausius-Mossotti equation. After the cessation of X-rays, the n(λ) of the films relaxes back to the original state, after a certain amount of time. The minimum time to relax to the equilibrium state after irradiation takes about 16 hours. The maximum changes in n(λ) and d were 0.27% and 0.27%. The changes in the optical band gaps, EgT and EgU, were within experimental errors ±0.04%. Changes in the optical constants induced by heating were measurably large. The changes in the optical constants by alloying with As and doping with ppm amounts of Cs have been also studied. Alloying with As increases n(λ) and decreases EgT, and further doping of Cs slightly increases n(λ)
      Degree
      Master of Science (M.Sc.)
      Department
      Biomedical Engineering
      Program
      Biomedical Engineering
      Supervisor
      Kasap, Safa
      Committee
      Chang, Gap Soo; Johanson, Robert; Yang, Qiaoqin
      Copyright Date
      June 2018
      URI
      http://hdl.handle.net/10388/8473
      Subject
      refractive index, Incident dose, Covalent Solid, Amorphous Selenium, Optical band gaps, Clausius Mossotti equation
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      • Graduate Theses and Dissertations
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