Beyond the Surface:\nInterconnection of Viscosity,\nCrystal Growth, and Diffusion in Ge<sub>25</sub>Se<sub>75</sub> Glass-Former

The knowledge of viscosity behavior, crystal growth phenomenon,\nand diffusion is important in producing, processing, and practical\napplications of amorphous solids prepared in different forms (bulk\nglasses and thin films). This work uses microscopy to study volume\ncrystal growth in Ge<sub>25</sub>Se<sub>75</sub> bulk glasses and\nthermally evaporated thin films. The collected growth data measured\nover a wide temperature range show a significant increase in crystal\ngrowth rates in thin films. The crystal growth is analyzed using near-surface\nviscosities obtained in bulks and thin films using nanoindentation\nand melt viscosities measured by a pressure-assisted melt filling\ntechnique. The crystal growth analysis provides information on the\nsize of the structural units incorporated into the growing crystals,\nessential for estimating the diffusion coefficients and explaining\nthe difference in crystal growth rates in bulk and thin films. The\ncrystal growth analysis also reveals the decoupling between diffusion\nand viscous flow described by the Stokes–Einstein–Eyring\nrelation. Moreover, to the authors’ best knowledge, the manuscript\nprovides the first evaluation estimation of the effective self-diffusion\ncoefficient directly from growth data in chalcogenide glass-formers.\nThe present data show a similar relation between diffusion coefficients\n(<i>D</i>) and crystal growth rates (<i>u</i>): <i>u</i> ≈ <i>D</i><sup>0.87</sup>, which is found\nin several molecular glasses.