In this work we report the effect of post deposition film treatment on the N0 2 sensing properties of CuPc thin films for room temperature operation. The gas sensitive response of the electrical conductivity to doping with N0 2 , doping with oxygen (in air) and cooling to 77K in liquid nitrogen are reported. The pretreatment with N0 2 is shown to improve the gas sensing properties by providing both an increase in the magnitude of the conductivity change for a given N0 2 concentration and a significant improvement in the recovery time. Data is analysed using an Elovich model, which suggests that the cooled devices have the best fit to this model; the data for the N0 2 doped devices suggest a Langmuir behaviour. For all devices, a simple time derivative of the change in current provides a measure of concentration for real time gas sensing applications.
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A practical approach for the modelling of the dielectric constants of thin composite films is presented. A general distribution function for composition fluctuations in the thin composite films is introduced to describe the transition from a non-percolative to a percolative morphology using physically meaningful parameters and is applied to model a wide range of experimental and simulated polymer–ceramic composite film behaviour from the literature, up to ceramic particle filler volume fractions of 75%. The parameters describing the morphologies of the various composites are used to predict effective dielectric properties with good accuracy. The model is applied further to composites that show early percolation behaviour, and the deviation of their effective dielectric behaviour from the standard effective medium theory at high filler volume fractions is discussed.
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