Metallic conductivity of amorphous carbon films under high pressure

Amorphous carbon films are prepared by plasma-assisted chemical vapor deposition. Resistivity of the films is measured from 300 down to 8 K showing a negative temperature coefficient of resistivity. An increase of room temperature conductivity from 102 S cm−1 to a value of about 104 S cm−1 is found at a pressure of 2 GPa. At a fixed pressure of 0.5 GPa, the films show a positive temperature coefficient of conductivity in the range from 300 to 200 K, followed by a very weak dependence of temperature down to 15 K. At a pressure of 2 GPa a positive temperature coefficient of resistivity is observed in the range between 300 and 15 K. The metallic behavior of the carbon films under high pressure is explained using electronic structure.