Wednesday, November 28, 2012
MRS Fall Meeting 2012 (Boston, MA)
Fabrication of Structured Nanocomposite Materials for Three-Dimensional Metamaterial Applications We present a technique that combines top-down and bottom-up nanofabrication approaches to create a structured nanocomposite material. The structured nanocomposite material consists of three-dimensional (3D) silver nanostructures embedded inside a doped polymer matrix. The positioning of silver structures within the matrix is controlled via femtosecond laser irradiation. The key is to use a material combination that yields a stable background dielectric matrix while allowing nanostructure growth inside the laser irradiated volume. We prepare samples that contain Ag+ ions inside a transparent polymer matrix. Femtosecond laser pulses are focused inside the matrix, inducing multiphoton photoreduction reactions. These reactions are localized to the focal volume of the laser and lead to the nucleation and growth of silver nanoparticles. Since the silver growth process is limited to volumes irradiated by the laser pulses, we can precisely control the location of silver nanostructures inside the polymer matrix and create 3D patterns. The nonlinear nature of the absorption process allows us to modify the transparent material in three-dimensions and obtain resolutions higher than the linear diffraction limit of the laser. We show sub-300 nm resolution silver structures. We create, for example, 3D arrays of disconnected silver nanostructures that are not feasible using other techniques. Samples are characterized using scanning electron microscopy, transmission electron microscopy, as well as optical techniques. 3D nanofabrication techniques are increasingly important for nanophotonics and metamaterials. Many applications in these fields also require the precise integration of multiple materials, such as metals with dielectrics. The presented technique is well suited for nanophotonic and metamaterial applications and can produce structures not feasible using other methods. The technique can also be applied to alternative material combinations, including other metals or semiconductors.