It is well known that by fabricating novel materials in a nano-structured form many of their properties can be enhanced. The present project is to infiltrate porous synthetic opals, which are periodic arrays of monodispersed silica spheres of diameters in the range 100-500nm, with thermoelectrically active materials. The aim of this approach is to decrease the overall thermal conductivity of such nanocomposites, and obtain enhanced thermoelectric properties. Due to 3-d regularity of the balls packing, the whole array of silica spheres acts as a 3-d optical grating; this type of gratings has recently begun to be called photonic crystals. The infiltration can be carried out such that the silica balls themselves are filled with the desired materials, or the tetrahedral or octahedral voids in these structures. Subsequent dissolving of the silica leaves various fascinating templates for creation of complicated matrices of opal replicas, made of various materials interesting for thermoelectricity. The infiltration itself can be achieved by pulsed laser deposition on to the opal or by chemical techniques. Various forms of these self-assembling systems along with their transport properties like thermoelectric power, electrical conductivity, magnetoresistance and optical properties are being studied. The nanostructures involved are investigated using atomic force microscopy.
We are currently developing a unique technique to measure thermopower at a high precision using a closed cycle refrigerator system. Specifically bismuth base alloys, and manganites are being investigated.