Hopping of electron transport in granular Cu_x(SiO₂)_1–x nanocomposite films deposited by ion-beam sputtering

Highlights: • Nanocomposites deposited in the argon ambient. • Cu_x(SiO₂)_1–x nanocomposite films (0.36 < x < 0.73, 3–5 μm thickness). • Formation of the "shells" is probably due to the partial oxidation of Cu nanoparticles. - Abstract: The paper presents investigation into the Cu_x(SiO₂)_1–x nanocomposite films (0.36 < x < 0.73, 3–5 μm 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 σ(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 (∼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