Design and synthesis of nanomaterials for surface-enhanced Raman scattering, fuel cell technology, and photonics

In the first part of my dissertation, I developed two approaches for selectively probing the SERS activities of individual hot spots, i.e., experimentally detect the SERS signals only for the molecules that are trapped within the hot-spot region in individual Ag nanoparticle dimers. Then, I performed a systematic investigation on the SERS activity of individual dimers composed of two closed spaced Ag nanoparticles. By utilizing Ag nanoparticles displaying a variety of well-defined shapes, sizes and orientations to construct the dimers, I were able to precisely correlate the detected SERS signals to the specific geometry of individual hot spots.;In the second part of this dissertation, I performed a systematic investigation on the galvanic replacement reaction between PtCl62- and Pd nanocrystals with well-defined shapes including octahedra, nanocubes, and nanorods. The resultant hollow Pd-Pt bimetallic nanostructures were employed as electrocatalysts for the oxygen reduction reaction (ORR). Our results demonstrated that the nanostructures derived from Pd octahedra displayed the highest ORR activity, being 1.7 times more active based on equivalent Pt mass than the commercial Pt/C. I also conducted a mechanistic study on the galvanic replacement reaction between AuCl4- and Pd nanorods. Differently from the Pd-Pt system, a new type of hybrid nanostructure in the tadpole shape consisting of a Au head and a Pd tail was obtained due to a localized galvanic replacement mechanism. As an extension of my work to develop new electrocatalysts for the ORR, a templateengaged reaction was utilized for the synthesis of RuSe2+delta nanotubes. The RuSe2+delta nanotubes were active towards the ORR and displayed no loss in activity in the presence of methanol, as opposed to commercial Pt/C.;Finally, the template-engaged reaction was applied to the synthesis of Se MSe (M = Zn, Cd or Pb) colloidal spheres having similar sizes but different compositions. They were utilized as building blocks to obtain 3D photonic crystals via self-assembly. Moreover, superparagametic properties could be obtained via the incorporation of Fe3O4 nanoparticles into the a-Se cores. Taken together, this represents a versatile approach to the synthesis of magnetoactive spheres with similar dimensions but a variety of compositions and properties.