Self-assembled heterostructures based on magnetic particles for photonic bandgap applications

We demonstrate self-assembly of magnetic particles floating on a liquid surface. The size of the particles can be in the millimeter to micron range. The in-plane ordering is due to magnetic repulsion between the particles in the confined region. The stability for mm-size particles is due to buoyancy forces and to the flat particle shape. 3D structures are prepared by a "layer-by-layer" technique. This allows the fabrication of 2D- and 3D-photonic bandgap (PBG) structures in the microwave range and hopefully in the infrared range. Computer simulations of the electromagnetic wave propagation at normal incidence for 3D structures containing up to six layers indicate existence of the stop-band. This is confirmed by preliminary microwave transmission experiments. The exact position of the stop band may be tuned by the external magnetic field through the change of the in-plane interparticle distance. We also report fabrication of functional microparticles such as polystyrene (PS) spheres containing magnetite and coated with gold nanoparticles. These microspheres will serve as building blocks for the tunable photonic crystals in the infrared.