Switching behaviour in polymethylmethacrylate thin films: the effects of blending, doping and temperature
Otieno, Siro Jacob
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The memory and threshold switching of polymethylmethacrylate (PMMA) thin film as a function of thickness, temperature, dopant concentration and blend composition has been studied in this research work. The thin films were prepared using solution casting method taking the constituents in right proportions. Pure PMMA and pure polyvinylchloride (PVC) thin film samples were prepared. Four samples of PMMA/PVC blend thin films with 25 to 100 percent PVC and seven samples of Iodine doped PMMA thin films with 0.9 to 4.1 Iodine were also prepared. All samples of iodine doped PMMA thin films with 0.9 to 4.1% Iodine were also prepared. All samples showed memory switching. The threshold voltage (Vth) was found to vary directly proportional to the squre of the film thickness. In the PMM/PVC blends Vth obeyed simple dilution law, varying directly proportional to composition. In the doped PMMA samples Vth increased with iodine concentration indicating an increase i disorder. In pure PMM Vth decreased with temperature. In pure PMM, the conductivity increased with temperature in OFF state showing a sharp increase at about 360K. The polymer exhibited metal like behavior in the ON state where the conductivity decrease with temperature. Conductivity increased with PVC concentration in the blends. For the doped PMMA the conductivity increased with dopant concentration in both the ON and the OFF states. The conduction mechanism could however not be described using the percolation model since conductivity critical exponents much larger than the universal critical exponent t=2 were required in order to fit the data. It was found that space charge limited (S.C.L.) current theory is a suitable model to explain conduction in films of doped and blended polymeric materials.