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 °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 ξ. 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.

Indomethacin: The Interplay between Structural Relaxation, Viscous Flow and Crystal Growth

“…However, a certain u kin -η decoupling was still identified in the fragile glasses at high viscosities (low temperatures nearing T g ). An alternative revision of the u kin -η decoupling was provided by Schmeltzer et al [ 76 ], who introduced a decoupling temperature T d , below which the decoupling between the diffusion and viscosity occurs, with the decoupling exponent being temperature dependent (a qualitatively similar finding was recently obtained for amorphous selenium [ 77 ]). An interesting alternative to the above-mentioned standard models for crystal growth is the approach of Martin et al [ 78 ], who introduced the “transition zone theory” based on the cooperating ensemble of structural entities driving the mechanistic formation of the crystalline phase.…”

Crystal Growth in Se–Te Chalcogenides: Overview of the Growth/Relaxation/Viscosity Interplay for Bulk Glasses and Thin Films

“…In addition to the macroscopic crystal growth explored by DSC, optical transmission microscopy was used to investigate the microscopic aspect of the crystal growth (utilizing the newly developed methodology of paired microscopy-DSC experiments introduced in ref ). The example of the typical micrographs is shown in Figure A–C; all observed Se–Te crystals exhibited similar morphology (round cylindritessee Supplemental online material for schematic representation of the cylindrites formation) and were randomly distributed throughout the films.…”

“…Similarly inconsistent behavior (although quantitatively different) is exhibited by the E values corresponding to the DSC crystallization in Se−Te powders, where the deviations are caused by the not always standardized influence of the mechanically induced defects. This might theoretically suggest that much closer attention needs to be paid to the quality of the microscopic observations of crystal growth in bulk chalcogenide materials, where no exact methodology (such as 32 for chalcogenide thin films) was developed. In particular, the improvements should be considered with regard to the following: pre-experiment annealing at T g to standardize the level of thermally induced stress, careful, and unified approach to the processing of the bulk glass (grinding and polishing can induce defects�that can both catalyze and hinder crystal growth�deep within the bulk sample 69 ), detailed recognition of different types of crystal growth (especially the non-homogeneous modes) in order to avoid mismatch, pairing the microscopic growth studies in bulk sample with identification of the ideal nucleation conditions (or negating this need by implementing parallel measurements if different-sized crystallites).…”

“…Similar state of affairs exists also for the Se–Te chalcogenide glasses, where the high-quality microscopic studies are very scarce − but inconsistent, and do not provide a complex perspective of the interconnection between the macro- and microscopic data. Acquirement of such overall view was enabled only recently, through a break-through advancement in direct combined observation of the calorimetric signal and microscopic insight under exactly similar conditions. The effectivity of the combined procedure also allows for processing large enough data sets to explore the influences of composition, synthesis, and measurement conditions on the crystal growth kinetics.…”

“…The general outcomes of the studies, − with regard to the crystal growth in thin Se–Te films, were the sometimes significantly faster growth in the films (compared to the bulk material), and disunity of the explanations thereof. It was shown in ref that in case of the Se thin film it is the physico-chemical quality of the substrate that is absolutely crucial for the rates of the nucleation and growth phenomena. In compliance with this new approach, the goal of the present paper is to provide an overview of the crystal growth behavior in the Se–Te chalcogenide thin films and bulk glasses.…”