Raman and AFM mapping studies of photo-induced crystallization in a-Se films: substrate strain and thermal effects1

Photo-induced crystallization (PC) is studied in amorphous selenium (a-Se) films deposited on glass with and without intermediate layers of indium tin oxide or polymer material. The spatial profile of PC domains is examined by co-localized scanning atomic force microscopy and Raman mapping. We also explore the thermal behavior of the onset and growth of PC in the a-Se films by Raman spectroscopy measurements at temperatures spanning the glass transition (Tg ∼ 313 K). In many films the onset time for PC shows a surprising discontinuity near Tg. Inserting a thin polyimide layer between the a-Se film and the substrate inhibits PC. Our results indicate that adhesion to a rigid substrate is important for promoting PC in a-Se films. We find that the discontinuities in the PC onset times, the shape of the mapping profiles, and the effects of having a soft polymer interface layer can be understood by a model that takes account of the substrate shear strain and its relaxation near Tg.