Megaelectronvolt ion irradiation effects in amorphous carbon: the roles of the C-H and C-C bonds

Abstract

The electronic excitation of the target atoms by megaelectronvolt ion bombardment is responsible for the initiation of a number of damage processes. In the work described here we discuss secondary-electron emission, loss of bound hydrogen, and graphite formation in amorphous carbon films under irradiation by heavy ions. A mechanism that appears to underlie these effects is that of C-H and C-C bond breaking by the secondary electrons that are generated along the track of the incident ion and which allow the transport of the ion's lost energy to regions away from track. Model calculations based on this mechanism are in agreement with the observations. The production by such ion bombardment of small graphite crystals in the poorly conducting amorphous carbon matrix allows the conductivity of the material to be changed continuously over a range of four orders of magnitude. This phenomenon and its possible applications are discussed.

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