Diameter-Controlled Germanium Nanowires with Lamellar Twinning and Polytypes

One-dimensional nanostructures with controllable morphologies and defects are appealing for use in nanowire devices. This paper details the influence of colloidal magnetite iron oxide nanoparticle seeds to regulate the radial dimension and twin boundary formation in Ge nanowires grown through a liquid-injection chemical vapor deposition process. Control over the mean nanowire diameter, even in the sub-10 nm regime, was achieved due to the minimal expansion and aggregation of iron oxide nanoparticles during the growth process. The uncommon occurrence of heterogeneously distributed multiple layer {111} twins, directed perpendicular to the nanowire growth axis, were also observed in ⟨111⟩-directed Ge nanowires, especially those synthesized from patterned hemispherical Fe₃O₄ nanodot catalysts. Consecutive twin planes along ⟨111⟩-oriented nanowires resulted in a local phase transformation from 3C diamond cubic to hexagonal 4H allotrope. Localized polytypic crystal phase heretostructures were formed along ⟨111⟩-oriented Ge nanowire using magnetite nanodot catalysts.