Neutron is a very powerful tool to investigate structure and dynamics of materials covering a wide range of length and time scales. In the neutron scattering and nanoscale materials laboratory, we develop new functional nanomaterials mainly using molecular self-assembly methods and utilize neutron and x-ray scattering techniques to understand the underlying mechanism of the self-assembling behavior. Recently, synthesis of single, binary or multi-component nanoparticle superlattices has attracted great attentions for a broad spectrum of potential applications as well as its own scientific merit. The nanoparticles superlattice is a nanoscale counterpart of atomic crystal in which atoms are arranged periodically. As the atomic crystals provide an extremely wide spectrum of properties depending on the type of atoms in the crystal and their crystalline symmetry, the nanoparticle superlattices can exhibit new emerging properties through collective coupling between nanoparticles. Since the nanoparticle superlattice can provide properties not available in nature, it is called metamaterial. Currently, our research efforts have been focused on synthesis of metallic, semiconducting and magnetic nanoparticles of a wide range of shape and size, and use those as building blocks to design and fabricate nanoparticle superlattices of different symmetries and length scale, resulting in exciting progress. We apply the superlattices for various applications including high sensitivity molecular sensing, green catalyst and also use them as test beds for fundamental understanding of various nanoscale phenomena including plasmonic coupling. Combined with nanoporous silica materials, we also use nanoparticles for efficient recovery of radioactive elements.