292 



THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



Single crystal graphite has a specific resistance of about 3.9 X 10~^ ohm- 

 cm parallel to its base plane^^, with a positive temperature coefficient^^ -^^ 

 of 0.009 deg C~^, values confirmed by measurements made in the present 

 study. Along the c-axis of the crystal, however, the specific resistance has 

 been reported to range from 0.01 ohm-cm^^ to 1 or 2 ohm-cm^^, a value more 

 than ten thousand times greater than that in the base plane. Measurements 

 made in the present study show the specific resistance along the c-axis to 



1 2 4 6 8 10 20 40 60 100 200 400 1000 4000 10,000 40,000 100,000 



FILM RESISTANCE IN OHMS 



Fig. 12 — Relationship between the thickness of a pyrolytic carbon film and its film re- 

 sistance. 



be approximately 0.01 ohm-cm, with a negative temperature coefficient of 

 about 0.04 deg C-^ 



In view of the pronounced anisotropy in the specific resistance of crystal 

 graphite, the relationship shown in Fig. 13 between the specific resistance of 

 the carbon film and the degree to which its crystals are preferentially ori- 

 ented with their base planes parallel to the direction of current flow is to 

 be expected. Even in the most highly oriented specimens, however, the 

 specific resistance is greater than 1 X 10~' ohm-cm, and this fact emphasizes 



