Effect of photoinduction in PANi/TiO2 heterogeneous structure on conductance of PANi component.

Abstract

A heterostructure consisting of a PANi and a TiO₂ layer was chemically deposited consecutively on a glass substrate to investigate the effect of photoinduction in the structure on the conductance of the PANi component. It has been found that in response to the excitation light, the conductance of the PANi component in the PANi/TiO₂ heterostructure exhibits a distinct mode to be different from that of a single pristine PANi layer. The features account for the effects of photoelectronic and electrochemical processes that associate with the photoinduction in the PANi/TiO₂ heterostructure. The photoelectronic effect involves the appearance of the excess charges photogenerated inside the heterostructure on the depletion region. Due to the thermal diffusion of excess charges across the heterojunction, the width of the depletion is altered, leading to a modification in the conductance of the structure components, including the PANi. The electrochemical effect, on the other hand, relates to the appearance of the reactive oxygen species of O₂ ^•-, OH^•- and H⁺ that are created outside the heterostructure surface due to the photoinduction. Acting as strong oxidants, the species play the role of extra acceptor-like dopants and donor dedoping agents that modify the oxidation state and then the hole density of the p-type semiconductor PANi. The initial modification causes a sudden drop in PANi conductance at the start. As the exposure is further prolonged, the oxidation degree of the PANi component is further altered; the initial PANi emeraldine salt is gradually inverted to the emeraldine base, resulting in a conversion of its conductance. The combination of two modifications is explained for the mixing responses in the conductance of the PANi component and the U-turn shape of its baseline.