The formation of paramagnetic centers in aged porous samples was studied by using electron paramagnetic resonance techniques. Samples which had been oxidized by aging in air at room temperature contained Pb as the predominant defect. These were formed at the interfaces between Si nano-crystallites and the amorphous oxide layer in which the nano-crystallites were embedded and which formed during aging. No other paramagnetic centers (such as the E center that was characteristic of thin dioxide layers on Si) were observed. This was attributed to the H passivation of E centers in O-rich porous structures, and to the instability of the E center when near to the interface. The Pb center was stable after  irradiation.

B.Pivac, B.Rakvin, L.Pavesi: Applied Physics Letters, 1994, 65[25], 3260-2