The electrical conductivity of poly-p-xylylene + CdS nanocomposites

The dependence of electrical conductivity on the concentration of CdS (c) and temperature (T) over the temperature range 10–300 K was studied for poly-p-xylylene-CdS (PPX + CdS) nanocomposites prepared by solid-state cryochemical synthesis. The results were discussed in terms of the heterogeneous conductivity model including various charge transfer mechanisms in various nanocomposite regions. Under the illumination of a film with c > 11 vol % by a daylight lamp, the conductivity increased, and the σ(T) dependence was metallic in character at low temperatures. The photoconductivity of films at larger concentrations c was caused by the appearance of photoexcited electrons in CdS nanoparticles, the separation of charges at the nanoparticle-matrix boundary, and percolation effects in films. The PPX matrix was shown to actively participate in electrical conductivity; electrons in this matrix jumped between phenyl rings. The experimental dependence of dark conductivity σ(T) at temperatures from 150 to 300 K was analyzed using the Mott hopping conductivity model with variable jump lengths. The main points of the Mott theory of hopping conductivity were discussed.