• George J Goldsmith

      Articles written in Bulletin of Materials Science

    • Photoconductivity in thin films of phthalocyanine

      Francis P Xavier George J Goldsmith

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      The photocurrent and electrolyte electromodulation (EEM) spectra of thin films of metal-free phthalocyanine (H2Pc) and of copper phthalocyanine (CuPc) were investigated. The modulation spectra yielded three distinct features around 1·61, 2·30 and 2·93 eV for H2Pc and around 1·63, 2·04 and 3·20 eV for CuPc. The spectral dependence maxima of photoconductivity correspond to the modulation spectra. These features are interpreted to indicate transitions at critical points, i.e. the existence of transitions between three valence bands, since Pc’s are p-type, and the lowest conduction band in Pc’s.

    • Photoconductivity of iodine-doped single crystals of phthalocyanine

      Francis P Xavier George J Goldsmith

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      Single crystals of metal-free phthalocyanine (H2Pc) and of copper phthalocyanine (CuPc) were grown in the presence of iodine vapour. The presence of iodine enhances the spectral dependence of photoconductivity of H2Pc in the visible region but of CuPc in the near-IR region. The dark current is decreased but the photocurrent is increased by one order of magnitude in iodine-doped H2Pc but in the case of iodine-doped CuPc both currents are increased by nearly three orders of magnitude. Introduction of iodine results in about one order of magnitude decrease in response time for both modifications. Thus the introduction of iodine into Pc crystals decreases the energy barrier for conduction and increases the drift mobility of charge carriers thereby enhancing the conductivity of the material.

    • Single crystal growth of organic photoconductors: phthalocyanine

      Francis P Xavier George J Goldsmith

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      An effective method of growing single crystals of organic photoconductors such as phthalocyanine in the presence of doping impurity such as iodine by vacuum sublimation is discussed in this paper. This method is very useful especially when an organic material does not have a melting point but decomposes above a particular temperature. So far, doping has been done by exposing the previously grown organic single crystals to the dopant vapour, but growing the crystal in the presence of dopant vapour makes the doped-crystal more efficient and stable. The photosensitivity as well as the photoconductivity of the doped crystals by this method increases significantly.

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