Self assemblies of nanocrystals: preparation, collective properties and uses

Self-organization of nanocrystals depends on the type of nanomaterial and the coating. With silver nanocrystals, the self-organization is partially perturbed by the latter. With cobalt nanocrystals, the size distribution and thus the self-organization is controlled by the amount of reducing agent added during the chemical reaction and not by the micellar solution. It is possible to make "supra" crystals of cobalt nanoparticles in a face centered cubic (fcc) structure. By applying, during the evaporation process, an external magnetic field to ferrite nanocrystals dispersed in solution, nanocrystal organizations markedly change with their coating. Hence tubes are obtained with nanocrystals coated with citrate ions whereas thick films are produced when the coating is replaced by dodecanoic acid. Collective magnetic properties due to the organization in tubes are observed with a behavior similar to that observed with nanowires. The use of nanocrystals as a mask to produce various patterns on silicon is described.