Kyeong Woo Choi

Enhancement of Donor–Acceptor Polymer Bulk Heterojunction Solar Cell Power Conversion Efficiencies by Addition of Au Nanoparticles

This research was supported by Future-based Technology Development Program (Nano Fields, 2010-0029321) and the WCU (World Class University) program (R32-2008-000-10142-0) through the NRF of Korea funded by the MEST. J. H. Park acknowledges the support from NRF of Korea funded by the MEST (NRF-2009- C1AAA001-2009-0094157, 2011-0006268). Research at UCSB was supported by the US Army General Technical Services (LLC/GTS-S- 09-1-196) and by the Department of Energy (BES-DOE- ER46535).

Au@Pd core–shell nanocubes with finely-controlled sizes

We report a facile method for the synthesis of highly uniform Au@Pd core–shell nanocubes with finely- and well-controlled sizes by seed-mediated growth. Using single-crystal seeds of Au spheres with a uniform size, we could reproducibly obtain Au@Pd core–shell nanocubes with a narrow size distribution ( 98%). Moreover, the size of the Au@Pd core–shell nanocubes could be finely and readily tuned in a controllable fashion from 11.4 to 41.1 nm in edge length by varying the concentration of Na2PdCl4, the amount of seeds, or both. We have also investigated the localized surface plasmon resonance properties of Au@Pd core–shell nanocubes as a function of Pd shell thickness.

Au@Pd nanostructures with tunable morphologies and sizes and their enhanced electrocatalytic activity

We report a facile method for the synthesis of Au@Pd nanostructures with controlled sizes and morphologies from flower-like to cuboctahedral shape by seed-mediated growth using Au nanospheres as seeds and cetylpyridinium chloride (CPC) as a surfactant. The use of CPC as a surfactant and its molar ratio with respect to Na2PdCl4 were critical factors to generate the Au@Pd nanostructures with flower-like morphology. In addition, the morphology of Au@Pd nanostructures could be easily controlled by changing the concentration of CPC in the reaction solution, where controlled reduction kinetics according to the concentration of CPC brought variety to the morphology of the Pd shell and eventually the Au@Pd nanostructures. The size of Au@Pd nanostructures could be also readily tuned in a controllable fashion by varying the concentration of Na2PdCl4. We also investigated the morphology-dependent electrocatalytic activities of Au@Pd nanostructures toward ethanol electrooxidation as a probe reaction. Thanks to their larger electroactive surface area and higher density of electroactive sites, the flower-like Au@Pd nanostructures exhibited 2.2 times enhanced electrocatalytic activity per Pd unit mass than cuboctahedral Au@Pd nanostructures.

Robust synthesis of gold rhombic dodecahedra with well-controlled sizes and their optical properties

Through the seed-mediated growth method in N,N-dimethylformamide (DMF)–water medium using trisodium citrate and poly(vinyl pyrrolidone) (PVP) as stabilizer, Au rhombic dodecahedra with a narrow size distribution ( 90%) could be reproducibly synthesized thanks to the robust formation of rhombic dodecahedra by DMF–water medium and surface stabilization by trisodium citrate. Moreover, the edge lengths of these Au rhombic dodecahedra could be readily controlled from 19 to 67 nm by varying the amount of seeds, concentration of HAuCl4, or both, and thus the localized surface plasmon resonance peak positions of the Au rhombic dodecahedra could be continuously tuned from 532 to 655 nm.

Size-controlled gold nano-tetradecapods with tunable optical and electromagnetic properties

The synthesis of novel branched Au nanocrystals with a well-defined and size-controllable dualistic structure, Au nano-tetradecapods, is presented. Using seed mediated growth and kinetically controlled reaction conditions, Au nano-tetradecapods with fourteen branches grown preferentially on the vertices of an Au rhombic dodecahedral core are obtained. The size of the branches is easily and readily controlled by simply varying the volume of HAuCl4 solution added or the reaction temperature, or both. The localized surface plasmon resonance peak of the Au nano-tetradecapods can be finely manipulated over a broad range of visible light through the selective tuning of their branch sizes. The enhanced and tunable electromagnetic properties of the Au nano-tetradecapods are numerically analyzed using the finite-difference time-domain method and they are experimentally applied as effective surface enhanced Raman scattering substrates as well. In addition, it is found that the branch/core size ratio derived from the dualistic structure is a critical parameter for determining and controlling the properties of Au nano-tetradecapods.