Colloidal inorganic nanocrystals have some remarkable features. They exhibit size-dependent optical properties and can form crystal structures which have a different phase from the bulk material. These characteristics make them appealing as biological labels or as components of light emitting diodes and devices but the potential applications are affected by the reproducibility of the features throughout an entire batch of nanocrystals. Synthesis can often result in inconsistent sizes, shapes, or other properties, generally caused by a number of variables such as heating, cooling, side reactions, and impurities in the mix. Therefore, the synthetic route used should not only provide reproducibility, but it must also be tunable to the application for which the nanocrystals are intended.
The new automated system from Berkeley consists of a robotic platform which mimics synthetic procedures by using robotics to dispense liquids; it has inlets for gases and a low thermal mass reactor array for high-temperature reactions. Yet, it also has the added advantage of being able to fabricate nanocrystals while maintaining precise control over the conditions used during the procedure.
A variety of nanocrystals with diverse properties, such as optimum photoluminescence efficiency in CdTe crystals, have been fabricated using the robotic platform. CdSe nanocrystals have also been produced with a size distribution that has just 0.2 % coefficient of variation across a multiple array of eight parallel reactors, over separate runs.
Delia Milliron of the Lawrence Berkeley National Laboratory explains the impact of an automated system such as this one. “This capability has allowed us to optimize synthetic conditions to achieve properties of interest for various applications. For example, narrow size distribution for assembly of superlattice films or high luminescence efficiency for solar collectors and bio-imaging.”
Previous attempts at producing a reactor capable of achieving such reproducibility and throughput have been restricted to a limited set of reagents and reaction conditions. Significantly, this new platform is capable of carrying out independent reactions in an array.
“The materials synthesized so far include semiconductors and rare earth doped phosphors,” Milliron tells Materials Today. “We are currently working on optimizing the synthesis of increasingly complex nanocrystals with this powerful new tool.”