Native Crystal Growth Revealed by a Joint Microscopy-Calorimetry Technique in (GeS2)0.1(Sb2S3)0.9 Thin Amorphous Films: A Critical Role of Internal Stress and Mechanical Defects

Abstract

A novel joint microscopy-calorimetry technique pioneered in the present thin film research was used to investigate the influence of the substrate type on the crystal growth in (GeS2)(0.1)(Sb2S3)(0.9) thin films crystallizing from the free surface. The explored temperature ranges were 205-285 and 210-350 degrees C for microscopy and calorimetry, respectively. Identical temperature dependences of the macroscopic and microscopic crystal growth rates, crystal growth activation energies (decreasing from 333 to 277 kJmol(-1)), and values of the Ediger's decoupling parameter (decreasing from 0.63 to 0.55) were obtained for as-deposited thin films on Kapton as well as white glass substrates, confirming the negligible influence of the substrate nature. However, both types of as-deposited films exhibited markedly accelerated crystal growth compared to the powdered thin film (scraped-off of the substrate), for which the formation rate of the crystalline phase was practically identical to the native behavior of bulk glass. This unambiguously confirms the marked influence of the crystal-growth-accelerating internal stresses being built up during the heating of the thin film firmly attached to the substrate, where each of the two materials has a different thermal expansion coefficient. The unmatched accuracy and resolution of the joint microscopy-calorimetry approach were demonstrated, with similar subtle intrinsic trends in the crystal growth behavior being recognized by both techniques. Future prospects of the simultaneous in situ polarization microscopy measurements of crystal growth in the as-deposited thin films were introduced and discussed.