LETTERS

Self-assembly1–4 of components larger than molecules intoordered arrays is an efficient way of preparing microstructuredmaterials with interesting mechanical5,6 and optical7,8 properties. Although crystallization of identical particles9,10 or particles of differ-ent sizes11 or shapes12 can be readily achieved,the repertoire of methods to assemble binary lattices of particles of the same sizes but with different properties is very limited13,14.This paper describes electrostatic self-assembly15–17 of two types of macroscopic components of identical dimensions using interactions that are generated by contact electrification18–20.The systems we have examined comprise two kinds of objects (usually spheres) made of different polymeric materials that charge with opposite electrical polarities when agitated on flat,metallic surfaces. The interplay of repulsive interactions between like-charged objects and attractive interactions between unlike-charged ones results in the self-assembly of these objects into highly ordered,closed arrays. Remarkably,some of the assemblies that form are not electroneutral— that is, they possess a net charge. We suggest that the stability of thes