Mu Sang Lee

Electrical and Optical Properties of Conducting Poly(3-hexylthiophene)/Multi-walled Carbon Nanotube System

Polymer multi-wall carbon nanotube (MWNT) composites were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use in solar cell applications. Multi-walled carbon nanotube (MWNT) poly(3-hexylthiophene) nanocomposites were synthesized by in situ polymerization of monomers in the presence of different amounts of MWNTs. A process is reported to efficiently disperse multi-walled carbon nanotube (MWNT) bundles in a semiconducting polymer matrix. A uniform dispersion of the nanotubes in the polymer matrix was obtained. Characterization of the nanocomposites and the effects of MWNT concentration and dispersion on the structural, optical and electrical properties were discussed. FTIR and Raman spectroscopic investigations of nanocomposites indicate that the polymer is wrapped on the nanotubes, taking up a rigid orientation through π-π stacking. The Hall voltage measurement is followed to monitor carrier concentrations and mobilities, instead of the device fabrication and hole mobility measurements.

Surface-enhanced Raman spectroscopy of Omethoate adsorbed on silver surface

We have investigated surface-enhanced Raman spectroscopy (SERS) spectrum of Omethoate (O,O-dimethyl-S-methylcarbamoylmethylthiophosphate). It is found significant signals in the ordinary Raman spectrum for solid-state Omethoate as well as strong vibrational signals absorbed on the silver sol surface which is prepared by γ-irradiation technique at a very low concentration. Effects of pH and anions (Cl-, Br-, I-) on the adsorption orientation are investigated as well. Two different adsorption mechanisms are deduced, depending on the experimental conditions. The sulfur atom or the sulfur and two oxygen atoms are adsorbed onto the silver sol surface. Among halide ions, Br- and I- are more strongly adsorbed onto the silver sol surface. As a result, the adsorption of Omethoate is less effective due to their steric hindrance.

THE INFLUENCE OF SUBSTRATE TEMPERATURE ON THE ELECTRICAL PROPERTIES OF ZnO FILMS PREPARED BY THE RF MAGNETRON SPUTTERING TECHNIQUE

ZnO thin films were grown by the RF magnetron sputtering technique at different substrate temperatures, from RT to 300°C. The crystallite size was calculated from XRD and the grain size was measured from AFM for different substrate temperatures. The influence of the substrate temperature on the electrical properties of the films was investigated through the Hall effect, and conductivity studies were performed under UV light illumination. The conductivity and the carrier mobility of the films were found to increase with increasing substrate temperature, which can be due to the grain-boundary-dominated conduction mechanism. The thermal activation energy and photosensitivity of the films were calculated, and the results are presented in this paper.

Preparation of Conducting Polyaniline/TiO 2 Composite Nanorods by the Radiolysis Polymerization Method

Conducting polyaniline-titanium dioxide composite nanorods were synthesized by gamma radiation-induced oxidative polymerization method in the presence of TiO2 nanoparticles and an oxidant. The structural, morphological, conducting and optical properties of the nanorods were studied using SEM, TEM, UV-vis absorption, X-ray photoelectron spectra, Fourier transform infrared spectra and X-ray diffraction. The formation of nanorods can be explained by the anisotropic growth rate. The formation of PAni-TiO2 composites were the result of free aniline cation-radicals and adsorbed aniline cation-radicals on the surface of TiO2 nanoparticles grow together with the aid of high energy gamma irradiation. Electrical properties were checked by standard four-point probes method and found 0.28 S/cm for bulk PAni and 0.15 S/cm for PAni-TiO2 composite nanorods. The PAni-TiO2 composite nanorods showed improved thermogravimetric stability compared to PAni homopolymers. Finally, the composite nanorods synthesized by the radiolysis polymerization method might be used potentially in industrial basis like charge storage and materials of solar cells for its excellent photovoltaic and absorption properties.

Conducting polyaniline-rutile TiO2 nanocomposites for the development of high-k dielectric materials

ABSTRACT Inorganic dielectrics encapsulated in an organic matrix are showing excellent promise as novel dielectric materials. In this work, firstly highly organized crystalline nanoparticles of rutile TiO2 were synthesized by acid hydrolysis of titanium isopropoxide at room temperature. Then we developed a novel dielectric material consisting of highly organized rutile TiO2/polyaniline (PAni) nanocomposites by in-situ chemical oxidative polymerization. The structural, morphological, conducting, and dielectric properties of the rutile TiO2/PAni nanoparticles have been evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission emission microscopy (HR-TEM), four-point probe technique, CV (Capacitance versus Voltage), and Impedance analyzer. The nanocomposites show 70 times higher permittivity compared to rutile nanoparticles and much higher compared to anatase/PAni (ES) nanocomposites at 10 MHz. Large interfacial polarizations, nanostructure, and dopant levels are the key factors for the large dielectric constant of the nanocomposites. The rutile/PAni (ES) nanocomposites might see potential uses in super-capacitors, gate dielectric in transistors, and capacitive-type gas sensors.