Colloidal Synthesis of Air-Stable Crystalline Germanium Nanoparticles with Tunable Sizes and Shapes

Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative heat-up method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 degrees C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructures. The Ge nanoparticles, which are fully air stable for more than 6 months, were characterized by XRD, TEM, HRTEM, EDS, XPS, DRIFT, and UV-visible spectroscopy.