Investigations of the optoelectronic behaviour of novel phthalocyanine Langmuir-Blodgett films.

A review of phthalocyanine materials is presented, their history, properties, applications, and potential. The two materials under investigation in this thesis (A410 H[2] and A40iso6 H[2]) are introduced as metal free, non-peripheral octa-substituted phthalocyanines, molecularly engineered for Langmuir-Blodgett deposition by M. Cook at the University of East Anglia. The Langmuir-Blodgett method is used to deposit the two materials in the Y-form, onto substrates of glass and gold plated glass, and on quartz with interdigitated platinum electrodes. Optical absorption spectra are obtained for the materials, and the linear relation between the absorption intensity and thickness confirmed. The variation in optical absorption with polarisation and angle of incidence is used to obtain the molecular orientation of the two phthalocyanines. The polarisation results confirm earlier observations. The molecular orientation angles (with respect to the substrate) obtained in this thesis are novel for these materials, and confirm the Herringbone alignment of molecular pairs. Surface Plasmon resonance is used to obtain a refractive index of 1.629, and a thickness of 17.2 nm for a 6 layer film of the A410 material. The electrical properties were measured using samples of the film deposited on substrates with interdigitated electrodes. The spectral photocurrent, conductivity, and activation energy under illumination were investigated for both materials. The electrical response of the films to temperature, voltage and gaseous environment is presented with the time dependent photocurrent response. The characterisation measurement techniques are discussed and suggestions for improvements and further work are made.