UV/visible spectrophotometry measurements, together with measurement of the temperature dependence of ac parameters G (conductance), C (capacitance) and tan (dielectric loss) for 20Hz<f<1MHz, and dc conduction, for 77K<T<300K, are performed for a number of vacuum-sublimed phthalocyanine compounds. Steady state electrical measurements and optical absorption experiments were performed on samples of sublimed heavy fraction rare-earth element, fluorochromium and lutetium bisphthalocyanine films. From the Arrhenius plot of ln(T) (where (T) is the conductivity at temperature T) it is found that two conduction regimes exist. The activation energy in the order 0.2eV at high temperatures (T > 162K) relates to the distance of singlet states below the conduction band. The low temperature activation energy indicates hopping conduction between localised states close to the Fermi level. Visible optical absorption and transmission spectra are obtained for 50nm thick sublimed films of heavy fraction rare-earth [HF(pc)(pc*)], gadolinium [Gd(pc)(pc*)] and thulium [Tm(pc)(pc*)] bisphthalocyanine compounds when they have undergone the postdeposition treatments of voltage-cycling to blue, voltage cycling to red and annealing at 393K for one hour; also for untreated fluorochromium phthalocyanine. The different post-deposition treatments produce different effects on the absorption spectra; in the case of annealing, this is attributed to the phase changes occurring in the films. The changes due to the voltage cycling are believed to be a result of oxidation processes taking place in the materials. Absorption data are also analysed in order to obtain information regarding the dispersion of refractive index and dielectric constants within optical frequency range. Absorption data are analysed in terms of a well known power law, and a value of 2.3eV is found for the optical gap E0. in HF (pc)(pc*)
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:295102 |
| Date | January 1995 |
| Creators | Exley, James Richard |
| Publisher | Sheffield Hallam University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://shura.shu.ac.uk/7110/ |
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