PHONON-SCATTERING IN LIGHTLY NEUTRON-IRRADIATED DIAMOND

We report measurements on the thermal conductivity of diamond irradiated with fast neutrons. Low levels of irradiation ( < 10(19) neutrons cm-2) create vacancies and small regions of disordered carbon, whereas heavy doses ( > 10(20) neutrons cm-2) initiate vitrification. In this sense diamond is similar to the well-studied case of irradiated quartz. Our results in the low-dose regime are consistent with additional phonon scattering in the irradiated material by the extended regions of disordered carbon. The size and concentration of these regions are derived from the thermal-conductivity data correlate with those determined from the infrared spectra as well as with those estimated from a radiation-damage model. A comparison is made between the thermal conductivity of the irradiated material and that of synthetic vapor-deposited diamond films.