Characterisation of imperfections in single crystals of high purity synthetic quartz
The work described in this thesis is a study of imperfections in high purity, low dislocation content synthetic quartz single crystals which are grown on a commercial scale by the General Electric Company. Hydrogen and metal ion impurities in quartz were studied using low temperature transmission Fourier Transform Infrared Spectroscopy, (FTIR). Incorporation of impurities in quartz was investigated using crystals which were doped with Al, Fe, Cr, Co, Ti, P, Cu and K. Orientation of hydroxyl impurities was determined using polarised infrared spectroscopy. Deuterated quartz crystals were grown and studied as analogues to high purity crystals. X-ray diffraction topography was used to evaluate crystal quality and to perform a study of quartz which had been treated by electrodiffusion, or sweeping. Crystal lattice strain and sweeping damage was studied using double crystal topography at the Synchrotron Radiation Source, (SRS), at the Daresbury Laboratory. Metal ion impurities were sh own to incorporate interstitially into quartz crystals. The only exceptions were aluminium and iron, which incorporated substitutionally. All the impurities studied introduced hydrogen impurities such as hydroxyl ions and water molecules into quartz. A relationship between impurity concentration and hydrogen content was clearly indicated. The 3200 cm-1 broad absorption band characteristic of impure and fast grown synthetic quartz was strongly implicated as being due to interstitially incorporated water molecules. The major hydrogen impurities in quartz were sodium hydroxide molecules which were preferentially aligned along the X, Y and Z growth axes. Hydroxyl ions were not incorporated directly from the growth solution. Sweeping was shown to induce the formation of a negative space charge in treated quartz which gave rise to inhomogeneous lattice strain. The strain was gradually relieved upon prolonged exposure to x-rays. A mechanism for the production and relief of lattice strain has been proposed. Sweeping produced surface damage on mechanically polished crystals but not on those treated by chemical polishing using hydrofluoric acid. No further detrimental effects of sweeping were observed. Double crystal topographic studies revealed two possible bulk defects in Quartz. The first of these was a previously unreported planar defect parallel to the X-Y plane of quartz. The second was possibly a planar defect associated with the cellular growth cells in the (00.1) growth sector of quartz. The validity of these observations was put in doubt by the possibility of defect projection from the silicon monochromator which had been used in double crystal studies.