After deposition, by evaporation under vacuum, of Al/Cu/Te. multilayer structures, annealing at 673 K or more for half an hour, under argon flow, allows CuAlTe2 films crystallised in the chalcopyrite structure to be obtained. The optical and electrical properties are interpreted by introducing the influence of impurity foreign phases present in the films. The optical properties are sensitive to the small Al2O3 domains randomly distributed into the CuAlTe2 polycrystalline matrix. The optical band gap is slightly increased (2.35 eV) by the presence of alumina. The conductivity measurements show that a short circuit effect can be induced by a binary Cu2−xTe degenerate phase present at the surface of the films. This effect can be suppressed by KCN etching of the samples that allows the superficial foreign phase to be dissolved.
Experimental results on electrical conductivity of both doped polypyrrole (PPy) powder and conducting poly(vinyl alcohol) (PVA) -PPy composite are presented. In each case, FeCl 3 has been used as the oxidizing-polymerizing agent. Results are interpreted on the basis of a model in which counter-ions act through their attractive potential by forming conducting ways between chains and allowing transverse conduction. In the case of PPy powder, the major contribution to conduction mechanisms is hopping between polaronic clusters. In the case of the composite, an additional contribution results from fluctuation-induced tunneling through thin insulating PVA barriers.
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