Ion beam induced amorphization in α quartz

The amorphization of α quartz induced by light and medium mass ion bombardment has been investigated by means of Rutherford backscattering spectrometry in channeling geometry, resonant nuclear reaction analysis and mechanical surface profiling. The single crystalline samples were irradiated at 77 K with H+, N+, Ne+ and Na+ ions at energies of 10–100 keV and fluences up to 5×1016 ions/cm2. Disordering of α quartz by ion bombardment was found to occur by three-dimensional nucleation and growth of defect agglomerates and, possibly, small, spatially separated amorphous zones in the still crystalline surrounding. The nucleation rate scales with the energy density FD in elastic collisions. Above a critical energy density EC=1.92(7)eV/at deposited by nuclear collisions (corresponding to a displacement rate of 0.04 dpa) a coherent amorphous layer forms at the depth of maximum energy deposition, which then grows towards the surface and into larger depths during continued ion bombardment. Mechanical surface profiling reveals large compressive stresses (∼1.5 GPa), built up at low fluences, which are released at higher fluences after the amorphous layer extends to the surface. The stress release is accompanied by a significant reduction of the atomic density by about 19%.