Nanoparticle ring formation in evaporating micron-size droplets

Self-assembly process of CoPt3 particles into a ring pattern (ring diameter ranging from 0.6 to 1.5 mum, particle diameter 6 nm) results from phase separation in the thin film of a binary mixture, giving rise to a bilayer structure and subsequent decomposition of the top layer into droplets. Evaporation of the droplet leads to a shrinking of its contact line, and the particles located at the contact line follow its motion and self-assemble along the line. (C) 2004 American Institute of Physics.