Amorphous carbon films deposited from carbon ions extracted from a discharge in fullerene vapor

Abstract

Amorphous carbon (a-C) films with physical properties ranging from diamond like to graphite like were deposited at rates of 1 μm/h under 10−6 Torr vacuum by extracting a molecular carbon ion beam from a pure carbon discharge in fullerene vapor. With ion energies fixed near 300 eV, substrate temperature and beam neutralization were the main process parameters controlling film properties. a-C stress and density increased with decreasing deposition temperature, ranging to greater than 3 GPa and 2.9 g/cm3, respectively. Room temperature conductivity ranged from 10 to 10−11(Ω cm)−1, with cool substrates and a well neutralized ion beam producing the most insulating films. a-C conductivity increased irreversibly after imposition of electric fields exceeding 108 V/m through the film planes. The high conductivities of films deposited without a beam neutralizer are attributed to phase changes resulting from dielectric breakdown driven by electric fields induced by surface charging. Conductivity data obtained for films deposited at different temperatures are discussed in the context of activated conduction, variable range hopping, and multiphonon assisted hopping transport processes.