Wei Hsuan Hung

Plasmon Resonant Enhancement of Carbon Monoxide Catalysis

Irradiating gold nanoparticles at their plasmon resonance frequency creates immense plasmonic charge and high temperatures, which can be used to drive catalytic reactions. By integrating strongly plasmonic nanoparticles with strongly catalytic metal oxides, significant enhancements in the catalytic activity can be achieved. Here, we study the plasmonically driven catalytic conversion of CO to CO(2) by irradiating Au nanoparticle/Fe(2)O(3) composites. The reaction rate of this composite greatly exceeds that of the Au nanoparticles or Fe(2)O(3) alone, indicating that this reaction is not driven solely by the thermal (plasmonic) heating of the gold nanoparticles but relies intimately on the interaction of these two materials. A comparison of the plasmonically driven catalytic reaction rate with that obtained under uniform heating shows an enhancement of at least 2 orders of magnitude.

A microscopic study of strongly plasmonic Au and Ag island thin films

Thin Au and Ag evaporated films (∼5u2009nm) are known to form island-like growth, which exhibit a strong plasmonic response under visible illumination. In this work, evaporated thin films are imaged with high resolution transmission electron microscopy, to reveal the structure of the semicontinuous metal island film with sub-nm resolution. The electric field distributions and the absorption spectra of these semicontinuous island film geometries are then simulated numerically using the finite difference time domain method and compared with the experimentally measured absorption spectra. We find surface enhanced Raman scattering (SERS) enhancement factors as high as 108 in the regions of small gaps (≤2u2009nm), which dominate the electromagnetic response of these films. The small gap enhancement is further substantiated by a statistical analysis of the electric field intensity as a function of the nanogap size. Areal SERS enhancement factors of 4.2u2009×u2009104 are obtained for these films. These plasmonic films can also ...

Laser directed growth of carbon-based nanostructures by plasmon resonant chemical vapor deposition.

We exploit the strong plasmon resonance of gold nanoparticles in the catalytic decomposition of CO to grow various forms of carbonaceous materials. Irradiating gold nanoparticles in a CO environment at their plasmon resonant frequency generates high temperatures and strong electric fields required to break the CO bond. By varying the laser power, exposure time, and gas flow rate, we deposit amorphous carbon, graphitic carbon, and carbon nanotubes. The formation of iron oxide nanocrystals catalyzes the growth of carbon nanotubes. Predefined microstructure geometries are patterned by moving the focused laser spot during the growth process, forming suspended single-walled carbon nanotube structures. Raman spectroscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy are used to characterize the resulting material. The localized nature of the plasmonic heating enables growth of these materials, while the underlying substrate remains at room temperature.

Optical manipulation of plasmonic nanoparticles, bubble formation and patterning of SERS aggregates

We present an optical method for patterning SERS (surface-enhanced Raman spectroscopy)--enhancing aggregates of gold nanoparticles, using a focused laser beam to optically trap the nanoparticles in suspension. At high laser powers, heat generated from the plasmonic excitation causes boiling of the aqueous suspension and the formation of gaseous bubbles of water vapor. By measuring the Raman peak of the hydroxyl bond of water, the temperature in the laser spot during the aggregation can be determined in situ. The hydrophilic nanoparticles are found to aggregate at the liquid-vapor interface. By allowing the suspension to dry, a ring of gold nanoparticles is deposited on the substrate, producing a highly SERS-active region. These aggregates are studied using optical microscopy, scanning electron microscopy and micro-Raman spectroscopy.

Synthesis of Strong Light Scattering Absorber of TiO2–CMK-3/Ag for Photocatalytic Water Splitting under Visible Light Irradiation

The enhanced water splitting photocurrent has been observed through plasmonic mesoporous composite electrode TiO2-CMK-3/Ag under visible light irradiation. Strong light absorption achieved from the integrations of ordered mesoporous carbon (CMK-3) and silver plasmonic nanoparticles (NPs) layer in the TiO2, which significantly increased the effective optical depth of TiO2-CMK-3/Ag photoelectrode. The carbon-based CMK-3 also increased the surface wetting behavior and conductivity of the photoelectrodes, which resulted in a higher ion exchange rate and faster electron transport. The synthesis of high crystalline TiO2-CMK-3/Ag composite photocatalyst was verified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pronounced enhancement of light absorption of TiO2-CMK-3/Ag photoelectrode was confirmed by UV/vis spectrophotometers. Two orders of magnitude of the enhanced water splitting photocurrent were obtained in the TiO2-CMK-3/Ag composite photoelectrode with respect to TiO2 only. Finally, spatially resolved mapping photocurrents were also demonstrated in this study.

Rapid prototyping of three-dimensional microstructures from multiwalled carbon nanotubes

The authors report a method for creating three-dimensional carbon nanotube structures, whereby a focused laser beam is used to selectively burn local regions of a dense forest of multiwalled carbon nanotubes. Raman spectroscopy and scanning electron microscopy are used to quantify the threshold for laser burnout and depth of burnout. The minimum power density for burning carbon nanotubes in air is found to be 244μW∕μm2. We create various three-dimensional patterns using this method, illustrating its potential use for the rapid prototyping of carbon nanotube microstructures. Undercut profiles, changes in nanotube density, and nanoparticle formation are observed after laser surface treatment and provide insight into the dynamic process of the burnout mechanism.

Study of the plasmon energy transfer processes in dye sensitized solar cells

We report plasmon enhanced absorption in dye sensitized solar cells (DSSC) over a broad wavelength range. 45% enhancement in the power conversion efficiency is observed with the inclusion of plasmonic gold nanoparticles (NPs). Photocurrent spectra show enhancement over the entire dye absorption range from 450 nm to 700 nm, as well as in the near infrared (NIR) region above 700 nm due to the strong plasmon-induced electric fields produced by the gold NPs. The plasmon-induced electric field distribution of the island-like gold film is also investigated using finite-difference-time-domain (FDTD) calculations. Furthermore, photoluminescence spectra are performed in order to rule out the mechanism of plasmon energy transfer through Forster resonance energy transfer.

Nano- and biomaterials for sustainable development

1Department of Chemical and Materials Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan 2Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824-1226, USA 3Department of Materials Science and Engineering, Feng Chia University, Taichung 40724, Taiwan 4Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China 5Amity Institute of Biotechnology, Amity University Haryana, Gurgaon 122413, India