Metal nanocluster metamaterial fabricated by the colloidal self-assembly.

A new bottom-up approach for fabricating the optical metamaterial is reported. An array of metal nanoparticle clusters can provide both electric and magnetic activity in the optical frequency region through the excitation of the collective plasmon resonance. A two-dimensional square array of gold nanoparticle clusters (nanoclusters) was fabricated by using the template-directed colloidal self-assembly. The optical measurements showed strong extinction peaks in the near-infrared region owing to the electric resonance supported by the nanoclusters. The peak positions were in excellent agreement with the numerical simulations. The metal nanocluster metamaterial represents a promising new architecture for an optical metamaterial that can be fabricated by a scalable bottom-up fabrication technique.