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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



carbon is produced, and Fig. 9 shows the hydrogen content of pyrolytic 

 carbon fihns produced from methane as a function of the deposition tem- 

 perature. 



While the atom planes within a crystal packet are parallel to each other 

 there is, in general, no regularity in the relative angular orientation of 

 adjacent packets, which are randomly oriented. However, under some cir- 

 cumstances, films can be produced in which the individual packets tend to 

 be oriented with their atom planes parallel to the substrate,^^ the degree 

 of orientation depending on film thickness and on the conditions of pyrolysis. 



900 925 



950 975 1000 1025 1050 1075 1100 1125 1150 1175 

 TEMPERATURE OF PYROLYSIS IN DEGREES CENTIGRADE 



1200 1225 



Fig. 9 — Dependence of the hydrogen content of pyrolytic carbon films on the temper- 

 ature of formation. 



Under these circumstances, when pyrolytic carbon is produced at constant 

 methane concentration, the degree of orientation at the surfaces of films 

 greater than 3 X 10~^ cm in thickness passes through a maximum value as 

 the pyrolyzing temperature increases. This maximum orientation occurs 

 at 1025 deg C, regardless of hydrocarbon concentration. For deposition at 

 constant temperature, the degree of orientation increases with the methane 

 concentration. 



Pyrolytic carbon can thus be pictured somewhat as in Fig. 10, which is 

 drawn approximately to scale and which shows the orientation of the crystal 

 axes within the packets and the orientation of the packets in the carbon 

 films. 



