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.