ION-BEAM DAMAGE TO QUARTZ CRYSTALS

Heavy-ion damage was produced in α-quartz (single-crystal SiO2) by bombarding with 4'He+ to Bi+ in the energy range of 15-200 keV, at both 300 K and ≤ 50 K. The samples were analysed in situ with Rutherford backscattering/channeling. using 1-2 MeV 4He+ ions; data were obtained from both the oxygen and silicon peaks, so that damage stoichiometry could be calculated. At low ion fluences (∼ 1010 - 10101 ions/mm2) the apparent damage level increases linearly with fluence. but at rates of about 3-19 times greater than predicted by the modified Kinchin-Pease equation [1]. At higher fluences (∼ 1011 - 1012 ions/mm2) the rate of damage increases with fluence for elastic energy deposition rates of less than ∼ 0.08 eV/atom, but remains constant for greater elastic energy deposition rates. At even higher ion fluences saturation of the damage occurs. It has been observed that the analysis beam creates damage at a rate dependent on the level of damage already present in the crystal: furthermore, the damage created hy the analysis ions appears to be predominantly due to the inelastically deposited energy. Strain effects seem to greatly exaggerate the level of damage indicated by simple channeling calculations [2]. A rough model is proposed to explain both the high rates of damage production and the nonstoichiometry of the damage. © 1990.