EXLEY, James Richard (1995). Electrical and optical properties of novel phthalocyanine compouns for sensor devices. Doctoral, Sheffield Hallam University.
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Exley_295102.zip - Accepted Version
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Exley_295102.zip - Accepted Version
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Abstract
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*)
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