Nucleation and growth of the amorphous phase in Na-irradiated quartz

alpha-quartz was irradiated with 50 keV Na+ ions at fluences between 5.10(12)/cm(2) and 5.10(16)/cm(2) and a temperature of 77 K. The induced damage and the related density alterations were monitored by means of Rutherford backscattering spectrometry in channelling geometry and by mechanical surface profiling, respectively. The depth distribution of the implanted Na was determined employing resonant nuclear reactions analysis. Since the ion range distribution agrees well with TRIM95-simulations, the latter code was also used to estimate the energy density F-D deposited in primary and secondary elastic collisions. The damage accumulation is subdivided into two fluence regimes. In the ''nucleation regime'', a Gaussian-like damage profile was found, which increases in height with increasing fluence phi. The relationship between the apparent damage and the deposited energy density was found to be highly non-linear, chi(phi, z) proportional to (phi.F-D)(3.2). At the critical fluence phi(c) = 4.9(3).10(13)/cm(2) a coherent buried amorphous layer has formed at the depth of maximum energy deposition. This amorphous layer then grows towards the surface and into larger depths. The damage accumulation in this ''growth regime'' (phi>phi(c)) can still be described by a power law, the exponent, however has changed to m = 0.1(1).