서울대 차세대융합기술연구원

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Publications

Conferences

Spatiotemporal features of nucleic acid hydration and their changes during denat...

IRMMW-THz 2015 - 40th International Conference on Infrared, Millimeter, and Terahertz Waves

Son H., Jeong J., Kim S., Park J., Jang J., Eom K., Park I., Park G.-S.

Abstract
Dynamics and structure of water network around nucleic acid have been subjects of intensive studies due to their contributions to biological process. Here, we identified spatiotemporal features of DNA hydration through examining fully-hydrated DNA solutions by THz spectroscopy. The results suggest the presence of weakly bound water beyond tight-binding hydration layer with the timescale of 11.6ps and the thickness of 7.6Å. Also, we will present changes in the hydration water during DNA denaturation at the conference. © 2015 IEEE.
Correlation between salt-induced change in lipid hydration water and inter-space...

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

Choi D.-H., Son H., Jang J.-M., Jeong J.-Y., Eom K.-H., Jin K.S., Park J., Park G.-S.

Abstract
Salt-induced change in water dynamics inside multi-lamellar vesicles (MLV) is experimentally studied with terahertz (THz) time-domain spectroscopy (TDS). The dielectric constants of lipids dispersed in NaCl solutions with different salt concentrations are measured. We find that the water molecules with fast relaxation time (∼100 fs) significantly increase with NaCl concentrations. Furthermore, by combining the THz TDS results with small-angle X-ray scattering (SAXS), we find a strong correlation between multi-lamellar spacing and the fast water fraction. This suggests that long-range hydration might be critical in membrane-membrane communications. © 2016 IEEE.
Dependence of water relaxation dynamics on lipid structure

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

Eom K., Jang J., Jeong J.-Y., Yang Y., Choi D.-H., Son H., Park I.-K., Kim S., Park G.-S.

Abstract
The water relaxation dynamics is measured for DMPC vesicle solution and LMPC micelle solution from the dielectric spectroscopy. Both lipid have a same headgroup, which is interacting parts with the surrounding water molecules, but the change of the water relaxation time with increasing lipid concentration shows opposite trend. The result suggests that one needs to consider the lipid structure in water when the hydration property is determined. © 2016 IEEE.
Precise determination of optical parameter of highly absorptive liquid in THz re...

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

Son H., Choi D.-H., Jeong J.-Y., Jang J.-M., Park G.-S.

Abstract
A new approach for precise complex optical parameter of highly absorptive liquid is proposed for transmission THz time-domain spectroscopy. Due to the nature of liquid, indirect measurement of sample thickness increases inaccuracy in optical parameter. Here, we reduced uncertainty in optical parameter through an algorithm optimizing sample thickness by Kramers-Kronig relations. Less than 2% error in absorption coefficient of water at 1THz is achieved in proof-of-concept experiment. This analysis technique can be of use in studies of water-based liquid such as biomolecular solution. © 2016 IEEE.
High-Q electronic fano resonances in metallic subwavelength slits

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

Kim S., Baek I.-K., Bhattacharya R., Hong D., Matlabjon S., Park G.-S.

Abstract
We have experimentally investigated electronical excitation of Fano resonances in subwavelength slits. These resonances can provide strong concentration of electromagnetic waves under subwavelength conditions in microwave and terahertz regime as analogous to plasmonic Fano resonances in optics regime. It is observed that the quality factors of the resonances become exceedingly high by introducing the structural asymmetry. High-Q subwavelength slits which also show Rayleigh-like scattering, can be employed in various electro-optical devices of microwave, terahertz and infrared region. © 2017 IEEE.
Is fast relaxation water really a free water?

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

Jeong J.-Y., Jang J., Patra A., Eom K., Park I., Yang Y., Kim S., Di Tommaso D., Park G.-S.

Abstract
The origin of fast relaxation water in the terahertz frequency range have been elusive for years. In this contribution we have experimentally investigated the change in dynamical structure of water in salt solution using broadband dielectric relaxation spectroscopy (DRS) in the GHz to THz region to study the fast water. Numerical simulations have been conducted to quantify the dynamical properties in the hydration shell of the ions, including rotational and translational residence times. As the amount of the fast water increases with salt solution concentration, the fraction of water molecules with zero or one hydrogen-bond (HB) is also increased. We can conclude that the fast water is composed of the free water and one hydrogen-bonded water. © 2017 IEEE.
Improved field emission from tungsten doped reduced graphene oxide

IVEC 2017 - 18th International Vacuum Electronics Conference

Bhattacharya R., Baek I.-K., Barik R.K., Kim S., Hong D., Kwon O., Sattorov M.A., Park G.-S.

Abstract
The emission capability of as prepared reduced graphene oxide (rGO) and tungsten doped reduced graphene oxide (W-rGO) film field emitter (FE) cathodes are investigated experimentally. It is observed that W-rGO films showed a highest emission current density of ∼ 800 A/cm2 at an applied DC electric field of 6.6 V/μm, which is far superior than the current density of ∼ 390 A/cm2 from an as prepared rGO film. Short stability test also showed that emission current is much more stable than the rGO films. These excellent improvements can be attributed to the doping of tungsten into the rGO film, which helped to repair the broken bonds thus lowering the turn on field. Also, tungsten gives the film an excellent mechanical stability and higher thermal load handling capability, which is very important to achieve a stable, high performance operation and long life. © 2017 IEEE.
Study on the beam-wave interaction in sine waveguide

2018 IEEE International Vacuum Electronics Conference, IVEC 2018

Lei X., Li Q., Wu G., Ding C., Wei Y., Yin H., Guo G., Wang W., Park G.

Abstract
A theoretical model for analyzing beam-wave interaction in sine waveguide (SWG) is proposed. The 'hot' dispersion equation of the beam with arbitrary thickness is obtained by regarding the electron beam as a moving plasma dielectric. Moreover, the formula of gain growth rate is carried out. © 2018 IEEE.
Hydrothermally prepared reduced graphene oxide free standing film as high curren...

2019 International Vacuum Electronics Conference, IVEC 2019

Hong D., Kim S., Hossain M.M., Min S.-H., Sattorov M., Park G.-S.

Abstract
Uniform, highly conductive, thin film field emitters are in immense need for future development of high power compact terahertz(THz) vacuum electronic devices(VED). Reduced graphene oxide(rGO) based free standing film as high current sheet beam cathode is fabricated by hydrothermal method. This hydrothermal method facilitates highly conductive, thin, compact film. We achieved to get few micrometers to sub-micrometer thick film which is much thinner than conventional vacuum filtered film resulting in higher field enhancement factor, current density, and current. This approach can successfully establish a fabrication method for uniform, thin high current field emitter for high power THz VEDs. © 2019 IEEE.
Enhanced radiation using Cerenkov effect in Fano metamerical

2019 International Vacuum Electronics Conference, IVEC 2019

Kim S., Hong D., Sattorov M., Hossain M.M., Min S.-H., Park G.-S.

Abstract
The Fano metamaterial provides a way of trapping and releasing electromagnetic waves in microwave and terahertz regime. We show that, by utilizing the electromagnetic properties, the efficiency of radiation power from the Cerenkov effect in our recently proposed metallic metamaterial is much larger than the one from the ordinary Cerenkov and Smith-Purcell effects. The optimization of the efficiency was numerically conducted by manipulating the quality(Q) factor of the trapped Cerenkov light. The proposed metamaterial is suitable for developing compact and highly efficient free electron lasers. © 2019 IEEE.

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