Direct micro-imaging of point defects in bulk SiO2, applied to vacancy diffusion and clustering

Electron spin resonance microscopy (ESRM) was employed in the evaluation of diffusion characteristics of point defects (E' paramagnetic centers) in amorphous SiO2. Samples were subjected to inhomogeneous gamma-irradiation creating a heterogeneous distribution of E'-centers in SiO2 substrates. The samples were measured by ESRM after preparation and following several heat treatment cycles. These measurements revealed pronounced changes in the distribution of the E'-centers due to the heat treatments. The defects' reorganization did not obey simple diffusion laws and they exhibited an attraction towards areas with higher initial concentration. This behavior was simulated by an empirical model, resulting in the evaluation of the defects' diffusion constant, its activation energy, and their characteristic attractive potential. This is the first time that ESR imaging is employed to directly obtain such type of fundamental information regarding the diffusion behavior and interaction of point defects. Copyright (C) EPLA, 2010