Seong Gi Jo

Dual-mode waveguiding of Raman and luminescence signals in a crystalline organic microplate

We demonstrate dual-mode waveguiding of Raman and luminescence signals using π-conjugated organic 1,4-bis(3,5-bis(trifluoromethyl) cyanostyryl)-2,5-dibromobenzene (CN-TSDB) microplates with single-crystal structure. The output Raman and photoluminescence (PL) spectra through the CN-TSDB microplates were recorded as a function of propagation distance using a high-resolution laser confocal microscope (LCM). Under 633 nm Raman excitation, which is outside the optical absorption of the microplates, the characteristic Raman modes of C–Br, –CF3, and –CC– aromatic stretching were clearly observed at the output points. The decay characteristics of the LCM Raman intensities were comparable to those of LCM PL intensities. The intermolecular π–π interaction of CN-TSDB has been enhanced by the attractive interaction between the CN group and Br atoms, which induces efficient polariton propagation and plays an important role in dual-mode waveguiding.

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

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 Å).

Gate-field dependent photosensitivity of soluble 1,2,4,5-tetra(5′-hexyl-[2,2′]terthiophenyl-5-vinyl)-benzene based organic thin film transistors

The photoresponsive current-voltage characteristics of organic thin film transistors (OTFTs) have been studied as a function of gate-bias. For the active layer of the OTFTs, soluble 1,2,4,5-tetra(5′-hexyl-[2,2′]terthiophenyl-5-vinyl)-benzene materials have been used, and the thickness of the active layers varied. The photosensitivity of the OTFTs was controlled through both gate-bias (Vg) and incident light power. With increasing incident light power, the photosensitivity decreased during the source-drain current actively varied with Vg [i.e., at on-state with accumulated hole channel (Vg<Vonset)], while it increased for Vg≥Vonset (at off-state without accumulated hole channel). These variations are caused by two kinds of photocurrent mechanisms: one based on the photovoltaic effect for Vg<Vonset and another based on the photoconductive effect for Vg≥Vonset. The maximum photosensitivity of OTFTs was found to be approximately 40 times higher in the on-state than in the off-state due to the contribution of ...

Waveguiding characteristics of surface enhanced Raman scattering signals along crystalline organic semiconducting microrod

The waveguiding of surface enhanced Raman scattering (SERS) signals was demonstrated by using organic semiconducting microrods (MRs) hybridized with functionalized gold nanoparticles (Au-NPs). Organic semiconducting 1,4-bis(3,5-bis(trifluoromethyl) styryl)-2,5-dibromobenzene (TSDB) crystalline MRs were fabricated as active optical waveguiding system using a self-assembly method. The static SERS effect and the enhancement of photoluminescence were simultaneously observed for the TSDB MRs hybridized with Au-NPs. The waveguiding characteristics of the SERS signals through the hybrid MR of TSDB/Au-NPs were investigated using a high-resolution laser confocal microscope (LCM) system. The enhanced output Raman characteristic modes of TSDB molecules were clearly observed along the hybrid MR of TSDB/Au-NPs, which is attributed to stronger scattering of the light and the increased coupling efficiency of waveguiding due to the presence of Au-NPs. The waveguiding of the SERS signals exhibited different decay constants for the corresponding characteristic Raman modes, such as -C = C- aromatic, -CF3, and C-Br stretching modes. The observed waveguiding characteristics of various SERS modes enable multi-modal waveguiding with relatively narrow spectral resolution for nanophotonic information.

Optically active charge transfer in hybrids of Alq3 nanoparticles and MoS2 monolayer

Organic/inorganic hybrid structures have been widely studied because of their enhanced physical and chemical properties. Monolayers of transition metal dichalcogenides (1L-TMDs) and organic nanoparticles can provide a hybridization configuration between zero- and two-dimensional systems with the advantages of convenient preparation and strong interface interaction. Here, we present such a hybrid system made by dispersing π-conjugated organic (tris (8-hydroxyquinoline) aluminum(III)) (Alq3) nanoparticles (NPs) on 1L-MoS2. Hybrids of Alq3 NP/1L-MoS2 exhibited a two-fold increase in the photoluminescence of Alq3 NPs on 1L-MoS2 and the n-doping effect of 1L-MoS2, and these spectral and electronic modifications were attributed to the charge transfer between Alq3 NPs and 1L-MoS2. Our results suggested that a hybrid of organic NPs/1L-TMD can offer a convenient platform to study the interface interactions between organic and inorganic nano objects and to engineer optoelectronic devices with enhanced performance.

Sensitive optical bio-sensing of p-type WSe2 hybridized with fluorescent dye attached DNA by doping and de-doping effects

Layered transition metal dichalcogenides, such as MoS2, WSe2 and WS2, are exciting two-dimensional (2D) materials because they possess tunable optical and electrical properties that depend on the number of layers. In this study, the nanoscale photoluminescence (PL) characteristics of the p-type WSe2 monolayer, and WSe2 layers hybridized with the fluorescent dye Cy3 attached to probe-DNA (Cy3/p-DNA), have been investigated as a function of the concentration of Cy3/DNA by using high-resolution laser confocal microscopy. With increasing concentration of Cy3/p-DNA, the measured PL intensity decreases and its peak is red-shifted, suggesting that the WSe2 layer has been p-type doped with Cy3/p-DNA. Then, the PL intensity of the WSe2/Cy3/p-DNA hybrid system increases and the peak is blue-shifted through hybridization with relatively small amounts of target-DNA (t-DNA) (50-100 nM). This effect originates from charge and energy transfer from the Cy3/DNA to the WSe2. For t-DNA detection, our systems using p-type WSe2 have the merit in terms of the increase of PL intensity. The p-type WSe2 monolayers can be a promising nanoscale 2D material for sensitive optical bio-sensing based on the doping and de-doping responses to biomaterials.

Nanojunctions in conducting polypyrrole single nanowire made by focused electron beam: Charge transport characteristics

A focused electron (E)-beam with various doses was irradiated on the intended positions of conducting polypyrrole (PPy) single nanowire (NW) to fabricate nanojunctions. The current-voltage characteristics and their temperature dependence of the PPy single NW with nanojunctions were measured and analyzed. By increasing the E-beam dose and the number of nanojunctions, the current level of the single NW was dramatically decreased, and the conductance gap became more severe as the temperature decreased. The charge transport behavior varied from three-dimensional variable range hopping to fluctuation induced tunneling models, depending on the dose of focused E-beam. From micro-Raman spectra, the focused E-beam irradiation induced the de-doped states and conformational modification of polymer chains in the nanojunctions. The results suggest that the nanojunctions made by focused E-beam acted as a quasi-potential barrier for charge conduction in the conducting PPy single NW.

Simulation of magneto‐optic readout signal spectrum using digitized mark and beam patterns (abstract)

This paper describes a simple and convenient simulation method, which uses analytical models for mark and beam patterns. The readout signal of optical disk system is obtained by two‐dimensional convolution of Gaussian intensity beam pattern and elliptical mark pattern. Then, signal spectrum is obtained by executing a fast Fourier transform algorithm after adding quantitative MO noise sources within bandwidth. For simulation, the two‐dimensional distributions of mark reflectivity and beam intensity were digitized, which enabled us to use easily available algorithm routines in digital signal processing. The resolution of the beam and mark patterns can easily be adjusted by changing the number of bits representing the patterns. Also, various noise sources in the MO disk system can be selectively added using random function generator. Simulated signal spectra were compared with experimental results. The parameters used were as follows: laser beam width was 780 nm, NA was 0.55, signal frequency was 9.4 MHz, du...