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 ofGe halides, and thermal decomposition of organogermane precursors. Here we describe an alternative "heat-up" method for the synthesis of size- and shape-tunableGe 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 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystallineGe form. By varying the concentration ofGeI ₄, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cubeshaped 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.