ELECTRON-IRRADIATION DAMAGE IN QUARTZ, SIO2

Crystallographically orientated samples of synthetic optical-grade col ourless quartz with high chemical purity and low dislocation density t ogether with synthetic,oem-grade amethyst with high Fe-concentration a nd ca. 250 H/10(6) Si (''dry'') or 600 H/10(6) Si (''wet'') and with v ery high dislocation densities were irradiated using TEM. Samples of c uts perpendicular ([c]-cuts) and parallel ([X]-cuts) to the c-axis, th at were as-grown or pretreated for 5 days at 820 K on air or under p(H 2O) = 10(8) Pa were prepared. Characterization methods used include AA S, FTIR, Raman-spectroscopy, X-ray-topography, REM, TEM in SAED and br ight-field mode and polarized light microscopy. Radiolysis was carried out in TEM from 10 to 300 K with 100 kV and from 70-850 K (low-high-t ransition temperature of quartz) with 200 kV. Irradiation damage was i nvestigated by decay of Kikuchi-lines or of Bragg-reflections in SAED and in bright-field mode by development of strain contrast centres and of noncrystalline volume areas. Special preparates where the irradiat ion damage was of microscopic dimensions were investigated using Raman -spectroscopy. Radiolysis of quartz is able to proceed at 10 K with me asurable velocity. The required electron dose for a standardized irrad iation damage decreases with increasing temperature. At ca. 500 K it g oes through a minimum and then increases steadily up to ca. 700 K. Fro m there the increase is steep until ca. 820 K where it culminates shar ply, showing strong fluctuations until 850 K. The [X]-cuts in the as-g rown state show significantly higher irradiation damage sensitivity th an [E1]-cuts. Dry or hydrothermal preheating increases the overall sen sitivity of irradiation damage and levels out the orientation differen ces. The high Fe-concentrations in amethyst in comparison with very pu re quartz have no detectable influence on the damage sensitivity. This is also true for different water concentrations independently from th e ratio of silanole-group to molecular water. Sample thinning by ion e tching with different gun currents produces differences in irradiation sensitivity. Thinning by crushing produces samples with sensitivities comparable with ion-etching at low gun current.