Photoconductivity of poly-p-xylylene + CdS nanocomposite films over a wide temperature range

• Published in: Russian journal of physical chemistry. B Vol. 5; no. 4; pp. 681 - 688
• Main Authors: Zhuravleva, T. S., Ivanova, O. P., Krinichnaya, E. P., Misurkin, I. A., Titov, S. V., Zav’yalov, S. A., Grigor’ev, E. I.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.08.2011
• Subjects: Chemical Physics of Nanomaterials; Chemistry; Chemistry and Materials Science; Physical Chemistry; photoconductivity; percolation cluster; electric double layer; perimeter of the cluster; dark conductivity; xylylene + CdS nanocomposites; poly; atomic force microscopy; thin films
• ISSN: 1990-7931; 1990-7923
• DOI: 10.1134/S1990793111040233

For poly- p -xylylene + CdS (PPX + CdS) nanocomposite films, the dependences of the photo-conductivity σ ph ( T ) on the concentration C of CdS nanoparticles, intensity and wavelength of exciting light, and temperature T within 15–300 K are examined. An appreciable photocurrent appears at C ≥ 10 vol %, when a large percolation cluster of CdS nanoparticles is formed. The photocurrent spectrum is compared to the absorption spectrum of the film. The photocurrent I ph ( P ) increases with the intensity of light flux P in a wavelength range near 435 nm according to the I ph ( P ) ∼ P n power law, where n < 1. At 15 K, the photoconductivity of films with C ≈ 11.5 and 13.5 vol % is higher than that of a pure CdS film ( C = 100 vol %) by factors of ≈100 and ≈30, respectively. For films with C > 11.5 vol %, the σ ph ( T ) dependence at low T exhibits a metal-like character (σ ph ( T ) decreases with increasing temperature). Atomic force microscopy is used to examine the surface topography of PPX + CdS films, which is found to be strongly dependent on the concentration of nanoparticles. The dark conductivity and photoconductivity of nanocomposite films arise due to the thermo- and photoexcitation transfer of electrons from the CdS nanoparticles to the PPX matrix with the formation of an electronic double layer at the PPX matrix-large percolation CdS cluster interface, a process that populates the phenyl rings of the adjacent PPX layer with excess electrons. As a result, various mechanisms of electron transfer in the polymer matrix can be realized: Mott’s hopping conduction mechanism with variable-range hopping in the matrix between CdS clusters and the metal-like behavior of the conductivity in the polymer shell of the large cluster at low temperatures. The polymer shell contains excess electrons on the phenyl rings -C 6 H 4 - in the composition of anion-resonances -C 6 H 4 − -.