Electron paramagnetic resonance spectroscopy of titanium-ion-implanted silica

Abstract

Silica substrates were implanted with titanium ions, in the +1 charge state, to nominal doses of 1×1016, 3×1016, and 6×1016 ions/cm2 at an energy of 160 keV and a current of 2.5 μA/cm2. The implanted ion depth profiles were measured by backscattering techniques. Components in the vacuum ultraviolet absorption and electron paramagnetic resonance (EPR) spectra are attributed to a fraction of the implanted titanium in the Ti3+ state. The intensity of the Ti3+ EPR component has a Boltzmann temperature dependence between 490 and 5 K. The fraction of implanted titanium ions producing this EPR component ranges from 10% for doses of 6×1016 and 3×1016 ions/cm2 to 38% for a dose of 1×1016 ions/cm2. Based on the relative intensities of the Ti3+ charge transfer band resolved in optical absorption measurements, the fraction of Ti ions in the 3+ state is larger than the fraction estimated from the EPR spectral component. The Ti3+ ions not contributing to the EPR spectra are assumed to be antiferromagnetically (or speromagnetically) coupled. The linewidth of the EPR component decreases with increasing implantation dose. The value for the exchange integral for the paramagnetic fraction of implanted titanium ions is approximately (1.3±0.4)×10−6 eV. The fraction of Ti3+ ions antiferromagnetically coupled increases with increasing ion concentration. Thus a smaller fraction of Ti3+ ions are detected by EPR as the implantation dose is increased. A greater fraction of the titanium ions are incorporated in the SiO2 glass substrate in the Ti3+ state by ion implantation than are introduced in the 3+ state by other techniques such as fusion, reduction of Ti4+, and flame hydrolysis.