Showing papers by "Jinsoo Joo published in 2012"

High-detectivity multilayer MoS(2) phototransistors with spectral response from ultraviolet to infrared.

Abstract: Phototransistors based on multilayer MoS(2) crystals are demonstrated with a wider spectral response and higher photoresponsivity than single-layer MoS(2) phototransistors. Multilayer MoS(2) phototransistors further exhibit high room temperature mobilities (>70 cm(2) V(-1) s(-1) ), near-ideal subthreshold swings (~70 mV decade(-1) ), low operating gate biases (<5 V), and negligible shifts in the threshold voltages during illumination.

Anisotropic optical absorption of organic rubrene single nanoplates and thin films studied by μ-mapping absorption spectroscopy

Abstract: Local absorption spectra and absorption coefficients were obtained from organic rubrene single nanoplates. Absorption along the b-axis was higher than along the a-axis for polarized illumination on an ab-faced single-crystal rubrene nanoplate, and the lowest crystal transition peak (∼530 nm) relatively increased in size with an increasing incidence angle due to the anisotropic absorption strength along the crystal axes. Rubrene thin films grown by organic molecular beam deposition displayed microscopically varying absorption spectra; the relative peak height of the M-polarized band and the overall absorption strength were strongest with polarized illumination along the c-axis.

Single nanoparticle of organic p-type and n-type hybrid materials: nanoscale phase separation and photovoltaic effect

Abstract: We fabricated hybrid nanoparticles (NPs) of p-type poly(3-hexylthiophene) (P3HT) and n-type fullerene derivative {[6,6]-phenyl C61-butyric acid methyl ester (PCBM)} materials through a mini-emulsion method. The nanoscale photoluminescence (PL) characteristics of the non-annealed and annealed hybrid single NPs with different concentrations of P3HT and PCBM were investigated using a laser confocal microscope (LCM) with high spatial resolution. The luminescence characteristics corresponding to the P3HT and PCBM materials were observed simultaneously in the LCM PL spectra for P3HT/PCBM hybrid NP after the annealing process. We propose that the annealing process for the hybrid NPs assisted the ordering of P3HT main chains and the formation of PCBM domains through the gathering of the molecules, indicating nanoscale phase separation. This was supported by UV-Vis absorption and Raman spectroscopy results. Conducting atomic force microscope experiments on an annealed hybrid single NP allowed for the measurement of the characteristic photoresponsive current–voltage curves, and monochromatic photovoltaic characteristics and the avalanche photodiode effect were observed in the low- and high-bias regions, respectively.

Electrospinning and optical characterization of organic rubrene nanofibers

Abstract: We report on the preparation of continuous organic rubrene nanofibers using the electrospinning method. We added the minimal amount of poly (ethylene oxide) in the electro-spinning solution to provide the viscosity required for electrospinning. Optical characteristics such as absorption, photoluminescence, and Raman spectra all confirmed the successful formation of rubrene nanofibers. Confocal Raman spectra obtained from single rubrene nanofibers showed co-existence of the amorphous and the crystal phase of the rubrene molecule. We also demonstrated that our rubrene nanofibers can be used as efficient optical waveguides. Our result suggests that abundant fluorescent, continuous nanofibers of small molecule materials can be successfully prepared using electrospinning.

Polarized photoluminescence characteristics of rubrene sheets with nanometer thickness

Abstract: We report on the temperature dependence of the polarized photoluminescence (PL) exhibited by crystalline organic rubrene sheets with a thickness of \ensuremath{\sim}60 nm. To probe the correlations between the electronic states and the molecular stacking of rubrene molecules, the polarized PL spectrum of a single rubrene sheet was analyzed as a function of temperature from 10 to 250 K. Drastic changes were observed in PL peak positions and intensities \ensuremath{\sim}100 and \ensuremath{\sim}170 K, which were likely related to variations in molecular ordering with temperature. The changes in the PL characteristics of the sheet \ensuremath{\sim}170 K are similar to those observed for rubrene bulk crystals, in terms of the enhancement of mobility and crystallinity. In addition, \ensuremath{\sim}100 K, the reversal of the relative ratio of PL intensities corresponding to two crystalline axes, $a$ and $b$, in the rubrene sheets suggested an anisotropic variation in the molecular ordering along these two crystalline axes.

Self-assembled monolayers made of 6-(5-((6-((5-hexylthiophen-2-yl)ethynyl)-9,10-bis(phenylethynyl)anthracen-2-yl)ethynyl)thiophen-2-yl)hexyl 3-(triethoxysilyl)propylcarbamate for ultrathin film transistors.

Abstract: A new functionalized triethoxysilane bearing an X-shaped, anthracene-based semiconducting molecule on one arm was designed and synthesized as a precursor for the preparation of a self-assembled monolayer (SAM) on a SiO2 substrate. 3-Isocyanatopropyl triethoxysilane was reacted with a monohydroxyl-terminated X-shaped, anthracene-based semiconducting molecule in the presence of tin catalyst. The 6-(5-((6-((5-hexylthiophen-2-yl)ethynyl)-9,10-bis(phenylethynyl)anthracen-2-yl)ethynyl)thiophen-2-yl)hexyl 3-(triethoxysilyl)propylcarbamate (BATHT-TEOS) was found to be stable and sufficiently reactive to form organic monolayers on hydroxylated SiO2 surfaces. The structures and properties of these SAMs were investigated using X-ray photoelectron spectroscopy, UV–vis absorption spectroscopy, photoluminescence (PL) spectroscopy, laser scanning confocal microscopy–PL spectrometry, and spectroscopic ellipsometry. In this work, BATHT-SAM was employed as an interfacial layer on SiO2 to fabricate ultrathin film transistor...

Photoluminescence and optical waveguiding characteristics of bisalkoxy tin(IV) porphyrin microcrystals

Abstract: Guide me: Laser confocal microscope photoluminescence (LCM-PL) and optical waveguiding characteristics for tin(IV) porphyrin-based microcrystalline rods and plates were investigated. The efficiency of optical waveguiding for the rods (0.04 μm(-1)) was five times better than for the plate, due to stronger π-π interaction and a short layer distance (3.035 vs. 3.328 A).

Plasmon‐enhanced Raman scattering of coaxial hybrid nanowires made with light‐emitting polymer and gold

Abstract: We report on the plasmon-enhanced Raman scattering of coaxial hybrid nanowires (NWs) made with light emitting poly(3-methylthiophene) (P3MT) and gold (Au) core or coating. Absorption spectra of coaxial hybrid NWs showed the absorption peaks because of localized surface plasmon (SP) excitation at ~ 567 and ~ 610 nm, in addition to the π–π* transition peaks of P3MT. Raman spectra of a single strand of coaxial hybrid NW and plain P3MT NW was obtained by using three different wavelengths of laser excitation of 514, 633, and 785 nm. We found that Raman intensities of hybrid coaxial NWs were enhanced by 4 to 15 times over those of plain P3MT NWs with the Raman excitation wavelengths close to the observed SP energies of coaxial NWs. We attributed the observed enhancement of the Raman signal to the resonance of the incident laser with the matching SP energies, rather than the possible doping level change, in hybrid coaxial NWs. Copyright © 2012 John Wiley & Sons, Ltd.