Electrical Properties of Arc-Evaporated Carbon Films

Abstract

Uniform thin films of carbon in the thickness range 100 to 2300 A have been prepared by arc-evaporation in vacuum. Evaporation rates were about 50 A/sec. The electrical properties of these films suggest that unannealed arc-evaporated carbon had less long-range order and was, therefore, more truly amorphous in structure than any other form of carbon yet obtained. After the films had been heated to 1200°K, however, their properties were similar to ordinary fine-particle carbon blacks, apparently as a result of increased ordering. The electrical resistivity of unannealed films followed Ohm's law, was not photosensitive, and could be well represented in the temperature range 77°K to 300°K by the equation R=AT−b, where b=5. When the carbon films were heated above room temperature, the resistivity and the exponent b were both decreased substantially. After the films had been annealed at 1200°K, the resistivity was reduced by a factor exceeding 800, and could be best represented, in the temperature range 77°K to 1200°K, by the equation R=α—βT. The values of the resistivity, temperature coefficient of resistivity, and thermoelectric power of the annealed films were then more nearly in agreement with the corresponding values for ordinary fine-particle carbon blacks. Other properties and applications of the films are discussed.