Formation of the ST12 phase in nanocrystalline Ge at ambient pressure

Abstract

Amorphous nanophase germanium can crystallize into a high-energy tetragonal phase (Ge-III/ST12) upon thermal annealing, particularly when prepared by the naphthalide-mediated reduction of GeCl₄ and subsequent treatment with t-BuMgCl. The formation of ST12-Ge is typically associated with high pressure, yet the nucleation and coalescence of this phase can be observed by in situ transmission electron microscopy at low pressure and at temperatures well below 200 °C, and can persist at temperatures of up to 500 °C. The low coalescence temperature of nanophase ST12-Ge suggests its compatibility with applications in direct-print electronics.