Seung Min Jin

Low-lying electronically excited states of C60 and C70 and measurement of their picosecond transient absorption in solution

Abstract Low-lying electronically excited states of C60 and C70 were identified in picosecond transient absorption measurements extending in wavelength down to 1000 nm. Spectral features in the near-infrared region were found to be significantly different from the results of previous studies. The lifetimes for S1 states of C60 and C70 were determined to be 1.3±0.2 ns and 0.7±0.05 ns, respectively. A simple energy diagram for electronic states of C60 and C70 is presented.

Single-molecule and single-particle-based correlation studies between localized surface plasmons of dimeric nanostructures with ~1 nm gap and surface-enhanced Raman scattering.

Understanding the detailed electromagnetic field distribution inside a plasmonically coupled nanostructure, especially for structures with ~ 1 nm plasmonic gap, is the fundamental basis for the control and use of the strong optical properties of plasmonic nanostructures. Using a multistep AFM tip-matching strategy that enables us to gain the optical spectra with the optimal signal-to-noise ratio as well as high reliability in correlation measurement between localized surface plasmon (LSP) and surface-enhanced Raman scattering (SERS), the coupled longitudinal dipolar and high-order multipolar LSPs were detected within a dimeric structure, where a single Raman dye is located via a single-DNA hybridization between two differently sized Au-Ag core-shell particles. On the basis of the characterization of each LSP component, the distinct phase differences, attributed to different quantities of the excited quadrupolar LSPs, between the transverse and longitudinal regimes were observed for the first time. By assessing the relative ratio of dipolar and quadrupolar LSPs, we found that these LSPs of the dimer with ~ 1 nm gap were simultaneously excited, and large longitudinal bonding dipolar LSP/longitudinal bonding quadrupolar LSP value is required to generate high SERS signal intensity. Interestingly, a minor population of the examined dimers exhibited strong SERS intensities along not only the dimer axis but also the direction that arises from the interaction between the coupled transverse dipolar and longitudinal bonding quadrupolar LSPs. Overall, our high-precision correlation measurement strategy with a plasmonic heterodimer with ~ 1 nm gap allows for the observation of the characteristic spectral features with the optimal signal-to-noise ratio and the subpopulation of plasmonic dimers with a distinct SERS behavior, hidden by a majority of dimer population, and the method and results can be useful in understanding the whole distribution of SERS enhancement factor values and designing plasmonic nanoantenna structures.

Detection of Biomolecular Binding Through Enhancement of Localized Surface Plasmon Resonance (LSPR) by Gold Nanoparticles.

To amplify the difference in localized surface plasmon resonance (LSPR) spectra of gold nano-islands due to intermolecular binding events, gold nanoparticles were used. LSPR-based optical biosensors consisting of gold nano-islands were readily made on glass substrates using evaporation and heat treatment. Streptavidin (STA) and biotinylated bovine serum albumin (Bio-BSA) were chosen as the model receptor and the model analyte, respectively, to demonstrate the effectiveness of this detection method. Using this model system, we were able to enhance the sensitivity in monitoring the binding of Bio-BSA to gold nano-island surfaces functionalized with STA through the addition of gold nanoparticle-STA conjugates. In addition, SU-8 well chips with gold nano-island surfaces were fabricated through a conventional UV patterning method and were then utilized for image detection using the attenuated total reflection mode. These results suggest that the gold nano-island well chip may have the potential to be used for multiple and simultaneous detection of various bio-substances.

Temperature-dependent photoluminescence study of C60 and C70

Abstract The photoluminescence (PL) spectra of C60 and C70 in toluene, as films on silicon and as KBr pellet, were obtained as a function of temperature. Different emission profiles are observed between the fullerenes in solution and in the solid form. The PL spectra of the C60 solids are similar regardless of their substrates, while those of C70 show different emission profiles between the films on silicon and the pellet, which is believed to be due to the substrate-dependent stacking disorder resulting from the nonspherical shape of the molecule. The changes in emission intensity and profile upon temperature are observed in the PL spectra of solid C60 and C70, suggesting the strong influence of rotational diffusion. The vibrational mode progressions are identified from the low-temperature photoluminescence spectra of C60 and C70.

High-precision measurement-based correlation studies among atomic force microscopy, Rayleigh scattering, and surface-enhanced Raman scattering at the single-molecule level.

We investigated the correlations among the structure, Rayleigh scattering, and single-molecule surface-enhanced Raman scattering (SERS) of DNA-tethered Au-Ag core-shell nanoparticles, especially in dimer and trimer forms. For the optimal correlation measurements, accurate information on the position of the nanoparticle is crucial for locating the nanoparticle at the center of the excitation source for the optical measurements. To achieve this, we developed a multistep correlation strategy that enables us to unambiguously correlate the AFM images with optical images within a few nanometers. We also newly defined the correlation accuracy in this paper as a useful concept for the correlation measurements. With this reliable correlation accuracy, we performed various statistical analyses to thoroughly elucidate the relationships between particle structure, Rayleigh scattering and SERS in terms of the incident polarization and scattering intensity ratio.

Silencing of Metallic Single-Walled Carbon Nanotubes via Spontaneous Hydrosilylation†

Noncovalent approaches havebeen considered appropriate to softly modify the surfaceproperties of carbon nanotubes sufficient for chemical andbiological applications. However, the importance of thedevelopment of covalent bond-forming chemical reactionshas recently been refocused on, since the strategically drivencovalent bonds are known to promptly alter the electricalproperties of carbon nanotubes to secure a high population ofsemiconducting carbon nanotubes from mixtures.

Combined micro-Raman/UV-visible/fluorescence spectrometer for high-throughput analysis of microsamples.

Combined micro-Raman/UV-visible (vis)/fluorescence spectroscopy system, which can evaluate an integrated array of more than 10,000 microsamples with a minimuma size of 5 microm within a few hours, has been developed for the first time. The array of microsamples is positioned on a computer-controlled XY translation microstage with a spatial resolution of 1 mum so that the spectra can be mapped with micron precision. Micro-Raman spectrometers have a high spectral resolution of about 2 cm(-1) over the wave number range of 150-3900 cm(-1), while UV-vis and fluorescence spectrometers have high spectral resolutions of 0.4 and 0.1 nm over the wavelength range of 190-900 nm, respectively. In particular, the signal-to-noise ratio of the micro-Raman spectroscopy has been improved by using a holographic Raman grating and a liquid-nitrogen-cooled charge-coupled device detector. The performance of the combined spectroscopy system has been demonstrated by the high-throughput screening of a combinatorial ferroelectric (i.e., BaTi(x)Zr(1-x)O(3)) library. This system makes possible the structure analysis of various materials including ferroelectrics, catalysts, phosphors, polymers, alloys, and so on for the development of novel materials and the ultrasensitive detection of trace amounts of pharmaceuticals and diagnostic agents.

Correlation studies between localized surface plasmons and surface-enhanced Raman scattering of Gold-Silver NanoDumbbells (GSNDs) at the single-particle and single-molecule level

Investigating the characteristics of the electromagnetic field generated inside plasmonically coupled metallic nanostructures with a small nanogap <1 nm is significantly important for the rational deign of plasmonic nanostructures with enormously enhanced electric field. Especially, plasmonic dimeric nanostructures have been heavily studied, mainly because of relatively easier structural reproducibility among the coupled multimeric nanostructures. However, controlling the geometrical structure with ~sub nm accuracy and the corresponding change in the magnitude of the electric field in a single dimeric nanostructure is still highly challenging, such that it is difficult to obtain reliable and reproducible surface-enhanced Raman scattering (SERS) signal essentially originating from the enhanced electric field inside the nanogap. This is indeed a critical issue because the SERS enhancement factors (EFs) exhibit a broad distribution (>106) with a long population tail even within a single SERS hot-spot, which could be largely attributable to subtle change in the plasmonic nanostructures and the random orientation and position of an analyte molecule within the plasmonic hot spot. Therefore, it is of paramount importance to systematically investigate a relationship between the geometry of nanostructure and the optical signals at the singlemolecule and single-particle levels.

Photodissociation Dynamics of Acetone in the Gas Phase and in Solution Studied by Transient Absorption and Femtosecond Stimulated Raman Spectroscopy

Photodissociation dynamics of acetone was investigated for the first time in the gas phase and also in solution by transient absorption and femtosecond stimulated Raman spectrscopy. In the gas phase, a Rydberg state with a decay time of 350 fs, which in solution decays at ∼100 fs. In solution. we also found evidence for solvated electron generation. Vibrational information about the photodissociation dynamics was investigated in the gas phase by femtosecond stimulated Raman spectroscopy. Vibrational peaks for the nR state were observed at 1835 cm−1 C = O stretching and at 3100 cm−1 for C−H stretching.