By using the spin-dependent recombination effect, a comparative study was made of paramagnetic surface recombination centers in crystalline and porous material. It was found that the electron paramagnetic resonance spectra of surface centers, which were detected by microwave photoconductivity, were the same in crystals and in as-prepared layers of porous material. A difference between the spectra of crystalline and porous material was found only after heat treatment.

R.Laiho, L.S.Vlasenko, M.P.Vlasenko: Materials Science Forum, 1995, 196-201, 517-22