Assembly of small building blocks such as atoms, molecules and nanoparticles into macroscopic structures—that is, 'bottom up' assembly—is a theme that runs through chemistry, biology and material science. Bacteria¹, macromolecules² and nanoparticles³ can self-assemble, generating ordered structures with a precision that challenges current lithographic techniques. The assembly of nanoparticles of two different materials into a binary nanoparticle superlattice (BNSL)^{3, 4, 5, 6, 7} can provide a general and inexpensive path to a large variety of materials (metamaterials) with precisely controlled chemical composition and tight placement of the components. Maximization of the nanoparticle packing density has been proposed as the driving force for BNSL formation^{3, 8, 9}, and only a few BNSL structures have been predicted to be thermodynamically stable. Recently, colloidal crystals with micrometre-scale lattice spacings have been grown from oppositely charged polymethyl methacrylate spheres^{10, 11}. Here we demonstrate formation of more than 15 different BNSL structures, using combinations of semiconducting, metallic and magnetic nanoparticle building blocks. At least ten of these colloidal crystalline structures have not been reported previously. We demonstrate that electrical charges on sterically stabilized nanoparticles determine BNSL stoichiometry; additional contributions from entropic, van der Waals, steric and dipolar forces stabilize the variety of BNSL structures.

1. IBM Research Division, T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, USA
2. Department of Applied Physics & Applied Mathematics, Columbia University, 200 SW Mudd Building, 500 West 120th Street, New York, New York 10027, USA
3. Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
4. †Present address: The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. *These authors contributed equally to this work

Correspondence to: Dmitri V. Talapin^1,4,5Christopher B. Murray¹ Correspondence and requests for materials should be addressed to D.V.T. (Email: dvtalapin@lbl.gov) or C.B.M. (Email: cbmurray@us.ibm.com).

Received 20 August 2005 | Accepted 2 November 2005

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