Amorphous Carbon Films: Conduction Across Metal/Carbon/Metal Sandwiches

Very thin films of evaporated carbon have been deposited on various metallic thin film and single-crystal substrates to form metal/carbon/metal sandwiches. Electrical conductivity measurements through the carbon, over a range of temperatures from room temperature to below 1°K, show that conduction is a process of complicated mechanisms dependent on the presence of both structural and impurity defects. At low temperatures, conductivity appears to be independent of temperature, and the carbon films may act as tunneling barriers of effective heights 30–100 meV. These heights can be engineered by suitable choices of evaporation and substrate conditions. Explanation of conduction in these films remains speculative.