Zee Hwan Kim

The initial observations of surface-enhanced Raman scattering (SERS) from individual molecules (single-molecule SERS, SMSERS) have triggered ever more detailed mechanistic studies on the SERS process. The studies not only reveal the existence of extremely enhanced and confined fields at the gaps of Ag or Au nanoparticles but also reveal that the spatial, spectral, and temporal behaviors of the SMSERS signal critically depend on many factors, including plasmon resonances of nanostructures, diffus

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTVibrational Control in the Reaction of Methane with Atomic ChlorineZee Hwan Kim, Hans A. Bechtel, and Richard N. ZareView Author Information Department of Chemistry, Stanford University Stanford, California 94305-5080 Cite this: J. Am. Chem. Soc. 2001, 123, 50, 12714–12715Publication Date (Web):November 20, 2001Publication History Received27 September 2001Published online20 November 2001Published inissue 19 December 2001https://pubs.acs.org/doi/1

A beam containing methane and molecular chlorine is expanded into a vacuum where the methane is excited with two quanta of C–H stretching (one quantum each in two of the four C–H bonds). The reaction is initiated by fast Cl atoms generated by photolysis of Cl2 at 355 nm, and the resulting CH3 and HCl products are detected in a state-specific manner using resonance-enhanced multiphoton ionization. Speed-dependent spatial anisotropies (βprod) of HCl and CH3 products allow identification of three m

Carbonyl sulfide (OCS) was photolyzed with linearly polarized 223 nm light and the sulfur-atom photofragment S(1D2) was probed by (2 + 1) resonance enhanced multiphoton ionization (REMPI) using alternatively left and right circularly polarized light. The measured orientation of the angular momentum was found to depend strongly on the speed of the sulfur atom photofragment: fast S atoms show a large orientation, whereas slow S atoms show little or no orientation. Orientation results from quantum

An apertureless near-field scanning optical microscope (ANSOM) that utilizes the enhanced field around a gold nanosphere, which is attached to the end of an atomic force microscope (AFM) tip, is used to image the local dielectric constant of the patterned metallic surfaces and local electric field around plasmonic nanosphere samples. A colloidal gold nanosphere (approximately 50 nm diameter) is linked to the extremity of the conventional etched-silicon probe. The scattering of laser radiation (6

Enhanced near-field distributions around a single gold nanosphere are imaged using scattering-type apertureless near field scanning optical microscopy (ANSOM) at a wavelength of 632.8 nm. For the first time, polarization-selected ANSOM images are obtained that show both the transverse (perpendicular to the tip axis) and the longitudinal (parallel to the tip axis) vector components of the near-field in a phase sensitive manner. A model calculation using a Green's dyadic propagator method successf

We demonstrate the synthesis and application of defect-engineered MoS₂ bilayers with enhanced reactivity and stability for high-performance hydrogen evolution reaction.

A beam containing CH(4), Cl(2), and He is expanded into a vacuum chamber where CH(4) is prepared via infrared excitation in a combination band consisting of one quantum of excitation each in the bending and torsional modes (nu(2)+nu(4)). The reaction is initiated by fast Cl atoms generated by photolysis of Cl(2) at 355 nm, and the resulting CH(3) and HCl products are detected in a state-specific manner using resonance-enhanced multiphoton ionization (REMPI). By comparing the relative amplitudes

A 4:1 mixture of CH4 and BrCl diluted in He are coexpanded into a vacuum chamber and the reaction of methane with atomic chlorine is initiated by photolysis of BrCl. Near 420 nm, the resulting mixture of ground- and excited-state chlorine atoms have spatial anisotropies of βphot=−0.7 for the Cl(2P3/2)+Br channel and βphot=+1.8 for the Cl*(2P1/2)+Br channel. The speed-dependent spatial anisotropy βrxn(ν) of the CH3(ν=0) reaction product is detected by 2+1 resonance-enhanced multiphoton ionization

Scattering-type apertureless near-field microscopy (ANSOM) provides high-resolution dielectric maps of indium gallium nitride (InGaN) semiconductor nanoparticles at visible (633 nm) wavelengths. A specific size-dependent contrast reversal is observed in the ANSOM images of InGaN nanoparticles grown on a layer of gallium nitride (GaN). Model calculations demonstrate that the observed contrast reversal is the result of the competition between the tip-particle versus tip-substrate dipolar coupling.

Molecular chlorine (Cl2) was photodissociated in the wavelength range 270–400 nm with linearly polarized light, and the orientation of the excited-state chlorine atom Cl*(2P1/2) was measured by 2+1 resonance enhanced multiphoton ionization (REMPI) using circularly polarized light. The degree of orientation of the Cl* photofragment is found to oscillate as a function of photolysis wavelength. The oscillation is a result of quantum mechanical coherence arising from electronic states of different s

Nanometer-scale chemical imaging of epitaxially grown gallium nitride (GaN) and indium nitride (InN) islands is performed using scattering-type apertureless near-field scanning optical microscopy (ANSOM). The scattering of 633 nm laser radiation is modulated by an oscillating metallic probe, and the scattered radiation is detected by homodyne amplification, followed by high-harmonic demodulation, yielding optical near-field scattering maps with a spatial resolution better than 30 nm. The image c

The local temperatures of a metal nanostructure and its adsorbate carry essential information about the energy dissipation dynamics, calling for nanoscale thermometry techniques. Here we present a surface-enhanced Raman scattering (SERS) thermometry method providing an accurate local temperature of the adsorbates: we use the ratios of anti-Stokes (aS) and Stokes (S) SERS vibrational peaks at the limit of zero (0) probe laser intensity, extrapolated from the spectra acquired with varying laser in

In various efforts to assure safety and serviceability of a bridge structure throughout its lifetime, it is essential to accurately estimate the traffic load effects. Although traffic loads involve large uncertainties and can vary significantly with site-specific traffic environments, bridge design codes and maintenance strategies do not utilize a probabilistic model that can reflect the actual environments and uncertainties of the target bridge. Rapid developments of weigh-in-motion (WIM) techn