Solid Phase Epitaxial Regrowth of alkali ion irradiated a-quartz

Abstract

The chemically guided epitaxy (SPEG) of the amorphized layer in synthetic a-quartz induced by 175-keV Rb or 50-keV Na ion implantations was investigated as a function of the thermal annealing in air or 18O2 atmosphere, the implanted alkali ion fluence, and the 18O2 oxygen pressure.Rutherford backscattering spectroscopy in channeling geometry (RBS-C) was used to determine the depth distribution of the damage and Rb concentration. The out-diffusion of the implanted Na and the 18O -16O exchange between the sample and the annealing gas were investigated by means of the Time-of-Flight Elastic Recoil Detection Analysis (TOF-ERDA).In the case of Rb implantation at a typical fluence of 2.5x1016 ions/cm2, complete epitaxial recrystallization was observed at very similar temperatures in air (1170 K) and 18O2 gas (1130 K). The regrowth process in air follows a two-step epitaxy (Arrhenius-type) with activation energies of EL = 0.6(2) eV and EH = 2.7(4) eV above and below an annealing temperature of 1070 K, respectively.The recrystallization rate was found to increase with increasing ion fluence and temperature, but to hardly depend little on the 18O2 pressure. Epitaxy occurred only above the critical temperature and alkali ion fluence.A strong correlation between the planar progression of the amorphous/crystalline interface, alkali ion out-diffusion, and 18O -16O exchange between the SiO2 matrix and the annealing gas was found. These results were explained with the help of the concept of the SiO2 network topology.The Atomic Force Microscope (AFM) images gave a clear view of the recrystallized structures and confirmed the fundamental influence of the temperature, ion fluence, and oxygen supply on the morphology of the recovered layer.The cathodoluminescence (CL) measurements were performed to identify different defect centers in the SiO2 matrix after Rb irradiation and their evolution during thermal annealing in air as well as in 18O2.