Medium-range order structures with 15-atoms cluster as building units in germanium nanoparticle film

The nucleation and growth dynamics of medium-range order (MRO) in germanium nanoparticle (Ge NP) films were studied using a combined approach of plasma-enhanced chemical vapor deposition (PECVD) and molecular dynamics (MD) simulations. Columnar-structured Ge NP films synthesized under optimized PECVD conditions displayed circular contrast features in high-resolution transmission electron microscopy, indicative of MRO formation. MD simulations of amorphous Ge (a-Ge), quenched at a rate of 4×10 9 K/s, revealed seven distinct atomic configurations of Ge 15 clusters, among which the type-I cluster acts as the primary fundamental building block for Ge 15 cluster-stacking columns (Ge 15 -CSCs). The simulations further showed that multi-axis Ge 15 -CSCs develop during structural evolution, with pentagonal dodecahedral Ge 20 cluster forming dynamically at the intersections of growing columns. Although Ge 15 clusters serve as essential nucleation sites for fivefold twin structures, Ge 20 cluster are not strictly required; instead, they act as kinetic facilitators that template the multi-axial assembly of Ge 15 clusters, thereby broadening the crystallographic routes available for fivefold twin nucleation.