Crystal Growth in Amorphous Selenium Thin Films-Reviewed and Revisited: Direct Comparison of Microscopic and Calorimetric Measurements

Abstract

A newly developed unique combination of direct microscopic and calorimetric measurements was used to study the crystal growth in amorphous selenium (a-Se) thin films (500 nm) deposited on Kapton tape and aluminum foil. The crystal growth rates (u(r)) microscopically determined in the 65-110 degrees C temperature range were similar to those for bulk selenium glass. The crystal growth kinetics was described in terms of the screw dislocation model with implemented temperature dependences of the growth activation energy E-G and Ediger's decoupling parameter xi. Extensive analysis of the literature data on the crystal growth rates in thin selenium films revealed the dominant effect of the number and distribution of the dangling bonds of the [Se](n) chains adjacent to the film/substrate interface. The seemingly scattered u(r)-T literature data were found to be consistent when the influences of impurities, substrate quality, illumination, and deposition conditions were accounted for. The macroscopic manifestation of the crystal growth in selenium thin films was observed by means of differential scanning calorimetry (DSC)-the corresponding activation energies were similar to the E-G values determined by optical microscopy; the Avrami equation with the implemented u(r) - T dependence was able to accurately describe the macroscopic DSC data. Additional DSC measurements for the selenium thin film scraped off the white glass substrate have shown that the above-T-g annealing of such a material suppresses the crystallization, which can be interpreted as the evidence of the dominant growth from the mechanically activated crystallization centers.