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 10(2) S cm(-1) to a value of about 10(4) 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. (C) 1997 American Institute of Physics.