Defect Structure of Crystalline Quartz. II. Variation of Displacement Threshold Energy with Crystal Growth Rate
An optical-absorption maximum (C band) is produced at about 220 mμ in crystalline quartz by electron bombardment at 77°K. The band is produced by the displacement of lattice atoms and not by ionization. Previously it was shown that the production rate of the band for constant integrated electron flux increases greatly with increased growth rate. In the present experiment, the threshold energy for the displacement which leads to C-band absorption was measured in synthetic crystalline quartz grown at 0.45 and 1.91 mm/day. Interpretations of the data lead to the conclusion that C-band absorption is caused by displacement of oxygen atoms and that the threshold energy for this displacement is a function of growth rate varying from 15+/-5 eV for fast-growth (1.91 mm/day) material to 50+/-5 eV for quartz grown at a slower rate (0.45 mm/day).