Hopping of electron transport in granular Cux(SiO2)1-x, nanocomposite films deposited by ion-beam sputtering

The paper presents investigation into the Cu-x(SiO2)(1-x) nanocomposite films (0.36 < x < 0.73,3-5 mu m thick) deposited by ion-beam sputtering of the compound Cu/SiO2 target in argon ambient. It has been shown that at x < 0.68 the studied samples displayed a hopping mechanism of electron transport, whereas beyond this concentration a metallic-like character of sigma(T) along the percolation net of Cu nanoparticles in the silica matrix was observed. Taking into account that at x = 0.68 associated with a much higher percolation threshold relevant to 3D metal-insulator composites (similar to 0.50), such a behavior can be attributed to the formation of the CuO2-based "shells" around the Cu "cores" observed by Raman spectroscopy. The formation of the "shells" is probably due to partial oxidation of Cu nanoparticles during the deposition procedure, resulting from the residual oxygen in a vacuum chamber after its filling with Ar gas. (C) 2014 Elsevier B.V. All rights reserved.