Seunghyun Cho

High-rate deposition of plasma polymerized thin films using PECVD method and characterization of their optical properties

Abstract Plasma polymerized organic thin films were deposited at temperature in the range of room temperature to 693 K by plasma enhanced chemical vapor deposition method using the thiophene (C4H4S) precursor. Radio frequency (RF) with 13.56 MHz was applied and the RF power was changed in the range from 30 to 100 W with a gas ratio of Ar:H2=1:1. The as-grown organic thin films were basically characterized with ellipsometry, UV–Vis spectroscopy, and photoluminescence (PL) measurements. In order to compare the difference of optical properties of the plasma polymerized organic thin films, the effects of the RF power and deposition temperature on their structural properties were mainly studied in this work. UV–Vis spectra showed an energy band gap shift from 3.78 to 4.02 eV with increasing RF power and quite high optical transmittance up to 95%. During CVD, moreover, the plasma diagnostics were in situ carried out by using optical emission spectroscopy that showed a strong dependency of intensity on RF powers. To check a possibility of optical device application, PL measurements were also carried out. From the PL data, we could obtain the maximum PL emission intensity at approximately 550 nm wavelength from a plasma polymerized organic thin film grown at room temperature and RF power of 70 W with gas ratio of Ar:H2=1:1. The maximum growth rate is obtained to be 115 nm/min.

Security Enhancement of User Authentication Scheme Using IVEF in Vessel Traffic Service System

Vessel Traffic System (VTS) is an important marine traffic monitoring system which is designed to improve the safety and efficiency of navigation and the protection of the marine environment. And the demand of Inter-VTS networking has been increased for realization of e-Navigation as shore side collaboration for maritime safety. And IVEF (Inter-VTS Data Exchange Format) for Inter-VTS network has become a hot research topic of VTS system. Currently, the IVEF developed by the International Association of Lighthouse Authorities (IALA) does not include any highly trusted certification technology for the connectors. However, the vessel traffic information requires high security since it is highly protected by the countries. Therefore, this study suggests the certification system to increase the security of the VTS systems using the main certification server and IVEF.

PET Fabric/Poly(3,4-ethylenedioxythiophene) Composite as Polymer Electrode in Redox Supercapacitor

Poly(ethylene terephthalate) (PET) fabric/poly(3,4-ethylenedioxythiophene) (PEDOT) composite with stable and high electrochemical activity was fabricated by chemical and electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) on a PET fabric in sequence. Effects of polymerization conditions on the following characteristics of the composite were studied: electrical conductivity and surface morphology. The electrochemical properties were also investigated by cyclic voltammetry and cyclic charge/discharge experiments. The specific volume resistivity, electrical conductivity and specific discharge capacitance of the composite were 0.034 Ω-cm and 25 S/cm, and 54.5 F/g, respectively.

Pet Fabric/Poly(3,4-Ethylenedioxythiophene) Composite with High Electrical Conductivity for EMI Shielding

Highly electrically conducting fabrics were prepared by chemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on a PET fabric. Monomer solution was prepared by dissolving EDOT and poly(vinyl pyrrolidone) (PVP) as a binder in 1-butanol. The oxidant solution was prepared by dissolving ferric p-toluene sulfonate (FTS) in 1-butanol. The mixture of the monomer and oxidant solutions was applied to PET fabric and polymerization was carried out under various conditions. We studied the effect of the chemical polymerization conditions on the properties of resulting composites such as electrical conductivity and surface morphology, environmental stability, electromagnetic interference shielding effectiveness (EMI SE). The specific volume resistivity, specific surface resistivity and EMI SE of the resulting composite were extremely low as 0.15 Ω · cm, 10 Ω/□ and quite high as 18 dB, respectively.

Synthesis and Thermal Properties of Liquid Crystalline Thermoset containing Rigid-Rod Epoxy:

4,4′-diglycidyloxy-α-methylstilbene (DOMS) and a novel liquid crystalline thermoset, D2A1 which is obtained from the reaction between DOMS and aniline were synthesized. The thermosets have been characterized with cross-polarized optical microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and other techniques. D2A1 was smectic at room temperature and turned to nematic at 85°C upon heating, then turned isotropic at 135°C. Activation energies for decomposition (E d) using TGA were calculated according to the technique of Flynn-Wall to determine E d as a function of conversion α by a weight loss process.

Synthesis of Polythiophenes with Electron-Donating Side-Chain and their Application to Organic Thin-Film Transistors

Thiophene-based π-conjugated polymers have been widely used in p-channel OTFTs due to their high charge carrier mobility. SPQT-12 which has dodecylsulfanyl side-chain was synthesized by Stille polymerization. The polymer was characterized by 1H NMR, GPC, UV-Vis spectroscopy, and cyclic voltammetry. Molecular weight (Mn) of SPQT-12 was 10,000 (PDI = 1.7), and SPQT-12 were readily soluble in common organic solvents. In the film state, SPQT-12 showed absorption with λmax at 553 nm and optical band gap of 1.87 eV. A mobility of 1.0 × 10−3 cm2/Vs, an on/off ratio of 5.8 × 103 and threshold voltage of −11 V have been obtained with OTFTs using SPQT-12.

Synthesis of Polystyrene Nanoparticles with Monodisperse Size Distribution and Positive Surface Charge Using Metal Stearates

Polystyrene (PS) nanospheres with a monodisperse size distribution, positive surface charge and high molecular weight were successfully synthesized using various types of metal stearates in an aqueous NaOH medium. The diameter of the PS nanospheres was controlled from 80 to 450 nm by changing the type of metal stearate. It was also found that controlling the NaOH concentration in solution was important for producing monodisperse PS nanoparticles. The nanospheres prepared with zinc stearate possessed a positive surface charge of 60 to 80 mV, confirming that PS particles were functionalized with metal stearates. It is believed that the metal stearates provide PS particles with not only colloidal stability but also a positive surface charge.

Thermally stable photoreactive polymers as a color filter resist bearing acrylate and cinnamate double bonds

Photoreactive polymers as a color filter resist containing both photoreactive acrylate and cinnamate double bonds were synthesized usin two step reactions. The chemical structures of the synthesized polymers were confirmed by1H-NMR and FT-IR spectroscopy. The photoreactive polymers were quite soluble in most common organic solvents and produced excellent quality thin films by spin-coating. The photocuring kinetics of the acrylate and cinnamate double bonds were examined by FT-IR and UV-Vis spectroscopy, which confirmed the excellent photoreactivity of both the acrylate and cinnamate double bonds in the polymers. Upon UV irradiation, photocuring was almost completed within approximately 5 min, irrespective of the type of the prepolymers. The polymers also exhibited superior thermal stability, showing little change in transmittance in the visible region even after heating to 250 °C for one hour. Photolithographic micropatterns could be obtained with a resolution of a few microns.

Feasibility Study of Development of Plastic Optical Fiber Temperature Sensor Using Thermosensitive Clouding Material

In this paper, we describe the feasibility of developing a new plastic optical fiber temperature sensor using a thermosensitive clouding material (TSCM) that changes its light transmittance with temperature. The temperature change in the TSCM gives rise to change in the turbidity of the TSCM, and the transmittance of the TSCM is altered according to the turbidity change. Light with a selected wavelength is transmitted to the TSCM, and the optical power of the reflected light from a reflector is measured using a Y-coupler made of plastic optical fibers.

Feasibility Study on the Development of Fiber-Optic pH Sensor for Endoscope

The general method to find a H. pylori in the stomach is the rapid urease test but it is only used to decide the infection with H. pylori. In this study, it is tried to develope fiber-optic pH sensor which can be used with gastroscop to quantify H. pylori. To measure the degree of infection with H. pylori, the color change of phenol red according to the degree of pH is measured by optical fibers with different light sources and the optimum distance from a sample to the end of sensor tip is decided by measuring the maximum reflectivity from a sample. Also the sensitivity study is carried out to decide the optimum light source which has sensitive change of reflectivity to the change of pH. It is expected that the fiber-optic pH sensor which measures the degree of infection with H. pylori exactly can be developed.