Domain and Dendrite Pattern Formation in PbSe Nanocrystal Monolayers

PbSe nanocrystal monolayers are deposited on ethylene glycol substrates as a function of nanocrystal surface concentration. Two different structural domains were encountered: low density (LD) domains composed of a close packing of nonattached crystals and high density (HD) domains made up of strings of oriented attached nanocrystals. For the lowest surface concentrations only LD layers form; at higher concentrations HD domains develop in the LD phase. Interestingly, at even higher concentrations LD seaweed type dendrites develop by diffusion transport in an extended and rapidly formed HD layer, densely populated with nonattached nanocrystals. The driving force for this remarkable dendrite growth is the rearrangement of the HD layers by mutual alignment, expelling nonbonded nanocrystals from these layers.