Nanostructured Materials: Self Assembly of Nanoparticles into Superlattices
Nanocrystals of different size and functionality (e.g. noble metals, semiconductors, oxides, magnetic alloys) can be induced to self-assemble into ordered binary superlattices (also known as opals or colloidal crystals) retaining the size-tunable properties of their constituents. The ability to tune interparticle separation and to build arrays based on a variety of constituents lends itself very well to the concepts of rational design of complex catalytic nanostructures.
Studying the formation mechanism for ordered multi-component nanoparticle superlattices not only provides opportunities to probe the unique physics of self-assembly in the nanometer scale, but also can potentially be utilized as a “bottom-up” design tool to build “metamaterials” of novel physical properties distinct from their individual components.
The self-assembly of multi-component nanoparticles can involve a complex balance between different driving forces such as entropy, Coulomb interaction from particle charges, London-van der Waals forces, and is a major part of our investigation. It has been suggested that a wide range of synergistic properties, especially optoelectronic, may emerge as a consequence of neighbor-neighbor interactions and it is therefore highly desirable to invent new methods to probe potential effects. An example might be size tunable energy transfer between semiconducing and metal nanoparticles within a superlattice.
Semiconducting Nanoparticle Superlattices. Top: Structure Direction in self-assembly: theoretical space-filling curves of close packed spheres following the raios AB5, AB13 and AB2. Bottom: TEM images of the corresponding binary superlattices.