Structural and electrical properties of Co xC 1− x nanogranular films prepared by pulsed filtered vacuum arc deposition

Abstract

Co x C 1− x ( x=0.18, 0.25, 0.39) nanogranular films were prepared by pulsed filtered vacuum arc deposition. Subsequent thermal annealing was performed in a vacuum furnace (∼8×10 −4 Pa) at various temperatures. The microstructural evolution of the films was characterized by non-Rutherford backscattering spectrometry, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the as-deposited films with various Co concentrations are amorphous. Upon annealing, nanocrystalline Co grains were formed, while the carbon content remained amorphous. The electrical resistance of the films was measured as a function of temperature between 20 and 300 K, using a conventional four-point probe DC technique. While the as-deposited films were metallic in the measured temperature range, annealed films showed complicated transport properties, depending on both the Co concentration and the annealing temperature. Experimental results are compared to the general predictions of theories of weak localization and/or electron–electron interaction on the metallic side of the metal-insulator transition, and thermally assisted hopping or tunneling on the insulating side of the transition.