Structure and electrical properties of Co$_n$(CoO)$_{100-n}$ thin-film composites

The electrical properties of Co$_n$(CoO)$_{100-n}$ composite thin films obtained by ion-beam sputtering of a composite target in an argon atmosphere and a mixed atmosphere of argon and oxygen (98% Ar + 2% O$_2$) have been studied. It has been established that if oxygen is introduced into the deposition chamber, the position of the percolation threshold shifts towards lower concentrations of the metal phase. It is associated with the special morphology of the films, when small metal Co nanoparticles are located along the boundaries of larger CoO particles, as well as a decrease in the size of inclusions of the metal phase. Studies of the temperature dependences of the electrical resistivity of synthesized Co$_n$(CoO)$_{100-n}$ films have shown that when the metal phase content is up to the percolation threshold the dominant mechanism of charge transfer in the temperature range of 80–140 K is the variable range hopping mechanism of conduction through localized states near the Fermi level, replaced by the nearest neighbors conductivity in the temperature range of 140–300 K. For beyond the percolation threshold Co$_n$(CoO)$_{100-n}$ thin films, the conductivity is determined by a network of metal granules and is characterized by a positive temperature coefficient of electrical resistance.