Structural defects in chromium-ion-implanted vitreous silica

Abstract

Structural defects and their concentrations have been determined in high-purity vitreous silica implanted with 0.5\ifmmode\times\else\texttimes\fi{}${10}^{16}$ to 6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ Cr ions/${\mathrm{cm}}^{2}$. Electron paramagnetic resonance (EPR) and optical-absorption spectra have been measured at 9.7 GHz and from 5 to 8 eV, respectively. A band with a peak around 7.5 eV increases with increasing dose and is attributed to a Si-Si bond similar to that in a ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$ molecule. This band has been called the Si-Si homobond. The concentrations of the homobonds and implanted Cr ions are of the same order of magnitude in the implanted layers at each dose level. A component of the EPR spectra is attributed to an E'-type paramagnetic state in which one of the Si bonds is to another Si, i.e., the Si-Si homobond. Another paramagnetic defect is the peroxy radical. The concentration of the E'-type center is high near the surface and decreases monotonically with depth. On the other hand, beginning at the surface the concentration of the peroxy radical increases to a maximum near the peak of the Cr-ion distribution and then decreases at greater depths. These complementary profiles suggest that oxygens are displaced in the direction of the ion beams and that these two defects are a paramagnetic Frenkel pair.