Effects of temperature on electron paramagnetic resonance of dangling oxygen bonds in amorphous silicon dioxide

The properties of electron paramagnetic resonance (EPR) signal of oxygen dangling bonds in amorphous SiO2 ("non-bridging oxygen hole centers", NBOHC) in excimer laser-irradiated amorphous SiO2 were studied in the temperature range 20K to 295K. NBOHCs strongly affect optical and chemical properties of amorphous SiO2 -based (nano) structures and their surfaces. The behaviour of their EPR signal is complicated due to a nearly degenerate electronic ground state. It was found that EPR signal has a non-Curie (similar to 1/T) T-dependence down to 40K, indicating that EPR-based concentration estimates routinely obtained at T=77K underestimate the center concentrations at least by a factor of 1.7. The estimates of NBOHC concentration, based on EPR, are typically similar to 10 times lower than those derived from optical spectroscopy, evidently due to incomplete accounting for temperature, microwave saturation and due to degenerate ground state coupled to disorder effects. The EPR signal of NBOHCs shows a strong microwave saturation at T<40K which allows for a high-sensitivity detection by 2nd-harmonic EPR registration techniques. Using it, the low intensity low-field wing of the EPR signal was shown to extend to g values as large as g=2.4.