In situ SHG investigation on the gelation process of organic doped silica film

The gelation process of organic doped silica film fabricated by the sol-gel technique was investigated by in-situ second harmonic generation (SHG) mea surements. The SH signal came from the doped hemicyanine molecules which au tomatically oriented in the film at or near the film-substrate interface. W e found that film shrinkage during gelation resulted in disordering of the doped hemicyanine molecules, so the SH intensity decreased during annealing . Thus, the SHG measurement can be used as a semi-quantitative probe of the gelation process in that particular region, which was hard to detect using conventional methods. We found that the time for gelation depends sensitiv ely on the annealing temperatures. The activation energy of the gelling pro cess was obtained from the SHG relaxation measurement. In addition, aggrega ted hemicyanine molecules dissociated with increasing annealing temperature . (C) 1999 Elsevier Science B.V. All rights reserved.