Sohyun Park

Pohang University of Science and Technology, Andong, North Gyeongsang, South Korea

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Publications (4)29.36 Total impact

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    ABSTRACT: Free induction decay of the coherent electronic transition and coherent phonon oscillations of the radial breathing mode in single-walled carbon nanotubes are simultaneously observed via direct resonant excitation of the lowest E(11) optical transition in the near-infrared region from 0.939 to 1.1 eV. We show that coherent electronic oscillations corresponding to the detuning of the probe energy from resonance can be exploited for the chirality assignment of carbon nanotubes, together with the robust assignment of the coherent lattice vibrations resonantly excited by femtosecond pulses. Excitation spectra show a large number of pronounced peaks that map out chirality distributions in great detail.
    Nano Letters 02/2012; 12(2):769-73. · 13.03 Impact Factor
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    Sohyun Park, June-Sik Park, Taiha Joo
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    ABSTRACT: We report a third-order nonlinear time-domain method, coherence period (τ) resolved transient grating (TRTG), that gives accurate solvation dynamics free from population relaxation in a short data acquisition time. The validity of TRTG is established by theory and experiment. The TRTG signal is shown to follow the transition frequency correlation function by an analytic expression based on the response function theory for delta function pulses and by model numerical calculations including finite pulse durations. TRTG is demonstrated for two cyanine dyes IR144 and IR125 in methanol by using a diffractive-optics based four wave mixing apparatus. Solvation dynamics in methanol obtained from the TRTG are consistent with those reported previously confirming the validity of TRTG.
    The Journal of Physical Chemistry A 02/2011; 115(16):3973-9. · 2.77 Impact Factor
  • Sohyun Park, Taiha Joo
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    ABSTRACT: We report a three-pulse photon echo peak shift (3PEPS) apparatus adopting a diffractive beam splitter to generate triplets of femtosecond pulses with tilted wave front, which enhances the overlap over the entire aperture in a noncollinear geometry while preserving femtosecond pulse duration. The apparatus provides highly reproducible 3PEPS data including the long time peak shift, a critical parameter to recognize the spectral inhomogeneity in condensed phases. To demonstrate the high performance of our setup and to examine the inhomogeneous line broadening in liquids, we measured 3PEPS of a carbocyanine dye IR125 in several solvents. The solvation dynamics becomes slower for IR125 compared to the typical values reported previously probably due to the multipolar nature of the excitation in this large and flexible probe molecule. More importantly, inhomogeneity was observed unambiguously in all solvents, and it is excitation energy dependent. It was speculated that slow dielectric relaxation and conformational heterogeneity may be responsible for the inhomogeneity.
    The Journal of Chemical Physics 10/2009; 131(16):164508. · 3.12 Impact Factor
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    ABSTRACT: Poly(3-hexylthiophene) (P3HT) hybrids with single-walled carbon nanotubes (SWNTs) were prepared using a series of SWNTs with various defect contents on their surfaces. The hybrids were synthesized by exploiting the π–π interaction between P3HT and the SWNTs, resulting in efficient dispersion of the carbon nanotubes in the P3HT solution. UV-visible and photoluminescence (PL) spectra showed that the carbon nanotubes quench the PL of P3HT in the hybrids, indicating that electron transfer occurs from photo-excited P3HT to the SWNTs. This electron transfer from P3HT to carbon nanotubes was disrupted by the presence of defects on the SWNT surfaces. However, the PL lifetime of P3HT in the hybrids was found to be the same as that of pure P3HT in solution, indicating the formation of a ground-state non-fluorescent complex of P3HT/SWNTs.
    Advanced Functional Materials 07/2008; 18(18):2659 - 2665. · 10.44 Impact Factor