Radiation Damage of Diamond by 20-keV Carbon Ions

Radiation damage in diamond due to bombardment by 20-keV C⁺ ions is observed from measurements of the optical reflection and transmission coefficients at wavelengths of 450, 500, 550, 600, and 650 m_μ. 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×{}10¹⁴ ions/cm². For a given specimen, the damage shows an initial saturation at 1.5×{}10¹⁴ ions/cm² 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 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 10¹².