Radiation Damage of Diamond by 20-keV Carbon Ions

Radiation damage in diamond due to bombardment by 20-keV ${\mathrm{C}}^{+}$ ions is observed from measurements of the optical reflection and transmission coefficients at wavelengths of 450, 500, 550, 600, and $650 m_{\mu }$. These measurements are analyzed to obtain the depth, refractive index, and absorption coefficient of the bombarded layer. The damage is found to be specimen-dependent with a typical increase in refractive index of 0.10 and an absorption coefficient of 0.065 per vacuum wavelength, for a bombardment of 9.4×${10}^{14}$ ions/${\mathrm{cm}}^2$. For a given specimen, the damage shows an initial saturation at 1.5×${10}^{14}$ ions/${\mathrm{cm}}^2$ with a subsequent slower increase in damage. The depth of the bombardment layer in all specimens is found to be about 0.056 μ for the 20-keV ${\mathrm{C}}^{+}$ ions. The damage is stable at room temperature and anneals gradually as the temperature is increased until complete annealing is obtained at 756°C. Analysis of the isochronal annealing curve shows that the activation-energy-of-motion spectrum for the bombardment-induced imperfections contains two major peaks which are calculated to be at 1.0 and 2.7 eV using a frequency factor of ${10}^{12}$.