Solution synthesis of germanium nanocrystals: Success and open challenges

We present a two-step synthesis route that yields nanometer-size crystalline germanium in the form of a black powder. It relies on high temperature decomposition of tetraethylgermane (TEG) in organic solvents. The presence of pure germanium with diamond structure is unambiguously attested by powder XRD measurements. Low-resolution TEM indicates that the particles are between similar to5 to 30 nm in size, depending on the synthesis conditions. The as-synthesized Ge powders can be stored in air for months and no oxidation occurs. The Ge powders are sparingly soluble in conventional solvents because Ge nanocrystals are likely embedded in a matrix composed mainly of C=C, C-C, and C-H bonds. The presence of residual organic byproducts impedes probing of the optical properties of the dots. Also, we discuss drawbacks and open challenges in high-temperature solution synthesis of Ge nanocrystals that could also be faced in the synthesis of Si nanocrystals. Overall, our results call for a cautious interpretation of reported optical properties of Ge and Si nanocrystals obtained by high-temperature solution methods.