A new X-ray topographic defect contrast on swept quartz crystals

X-ray topographic studies are made on vacuum-swept α-quartz crystals. A strong defect contrast is observed on X-ray topographs near the anode side of the crystal. This contrast disappears when the crystals are subjected to prolonged X-ray irradiation. The presence of this unusual contrast is attributed to lattice strains due to the collection of space charges near the anode side during vacuum sweeping. The negative space charge so formed is compensated by forming Al-OH and Al-hole centres during irradiation.