An investigation was made of the electron paramagnetic resonance of centers which were produced in porous material by heat treatment in vacuum. Annealing at temperatures ranging from 400 to 600C, under vacua of up to 5 x 10-5Torr, increased the electron paramagnetic resonance line intensity of Pb centers in a manner which depended upon the annealing time. This could be explained in terms of H de-passivation of the Pb centers. An isotropic line, with g = 2.0055 (which was usually attributed to disordered Si dangling bonds), appeared after vacuum annealing for some minutes. However, its intensity decreased after longer heat treatments. At room temperature, this decrease was exponential; with a time constant of a few minutes (depending upon the level of the vacuum). Heat treatment of the porous material in a vacuum led to amplification of the Pb electron paramagnetic resonance spectrum after exposing the samples to air at room temperature.

R.Laiho, L.S.Vlasenko: Journal of Applied Physics, 1995, 78[4], 2857-9