Self assembly of inorganic nanocrystals in 3D supra crystals: Intrinsic properties

Abstract

Here we describe how arrangements of nanocrystals can self-organize in 3D arrays called supra crystals. The 3D arrays can fall into the familiar categories of face centered cubic (fcc), hexagonal compact packing (hcp) crystals, and body centered (bcc) crystals. Intrinsic collective properties of these 3D arrangements are different from the properties of individual nanoparticles and from particles in bulk. We demonstrate by two various processes and with two types of nanocrystals (silver and cobalt) that when nanocrystals are self ordered in 3D superlattices, they exhibit a coherent breathing mode vibration of the supra crystal, analogous to a breathing mode vibration of atoms in a nanocrystal. Comparison between the approaches to saturation of the magnetic curve for supra crystals and disordered aggregates produced from the same batch of nanocrystals is similar to that observed with films or nanoparticles either highly crystallized or amorphous.