Soon-Wook Jeong

Enhancement of hole injection using ozone treated Ag nanodots dispersed on indium tin oxide anode for organic light emitting diodes

The authors report the enhancement of hole injection using an indium tin oxide (ITO) anode covered with ultraviolet (UV) ozone-treated Ag nanodots for fac tris (2-phenylpyridine) iridium Ir(ppy)3-doped phosphorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy and UV-visible spectrometer analysis exhibit that UV-ozone treatment of the Ag nanodots dispersed on the ITO anode leads to formation of Ag2O nanodots with high work function and high transparency. Phosphorescent OLEDs fabricated on the Ag2O nanodot-dispersed ITO anode showed a lower turn-on voltage and higher luminescence than those of OLEDs prepared with a commercial ITO anode. It was thought that, as Ag nanodots changed to Ag2O nanodots by UV-ozone treatment, the decrease of the energy barrier height led to the enhancement of hole injection in the phosphorescent OLEDs.

Characteristics of Flexible ITO Electrodes Grown by Continuous Facing Target Roll-to-Roll Sputtering for Flexible Organic Solar Cells

The preparation and characteristics of flexible indium tin oxide (ITO) electrodes grown on polyethylene terephthalate (PET) substrates are described for use in flexible organic solar cells and prepared using a specially designed facing target roll-to-roll sputtering (FTRS) system. Due to the effective confinement of the high-density plasma between two facing ITO targets, we can deposit the ITO electrode continuously on the PET substrate at a substrate temperature below 50°C without the need of a substrate cooling system, which is used in conventional roll-to-roll sputtering systems. In spite of a low substrate temperature, the FTRS-grown flexible ITO electrode showed a sheet resistance of 42.2 Ω/square, a resistivity of 8.44 × 10 -4 Ω cm, and a transmittance of 85.41% in the 500-550 nm wavelength range with superior flexibility. Furthermore, the flexible organic solar cell fabricated on the FTRS-grown flexible ITO electrode at optimized conditions exhibited a power-conversion efficiency of 2.43%, which is similar to an organic solar cell fabricated on a reference dc sputter-grown ITO electrode. This indicates that the FTRS technique is a promising continuous-sputtering process for preparing flexible ITO electrodes and can substitute for conventional roll-to-roll sputtering systems for mass production of flexible solar cells.

Finite Element Analysis of Diaphragm-type Air Springs with Fiber-reinforced Rubber Composites

This paper is concerned with deformation analysis of diaphragm-type air springs, especially an air bag which consists of nylon fiber-reinforced rubber, composite rubber linings and steel wire bead parts. The analysis has been carried out with a finite element code developed to consider the orthotropic properties of fiber-reinforced rubber lamina, geometric nonlinearity by large deformation, and contact between an air bag and a bead ring. Five different models have been considered in the design optimization procedure in order to investigate the effect of design variables with the variation of the cord angle of an air bag. The analysis provides the hoop and the longitudinal strain distributions in an air bag as well as the variation of the outer diameter, the fold height and the vertical force with respect to the internal pressure.

Room Temperature Fabrication of Organic Flexible Displays using Amorphous IZO Anode Film

We report on the fabrication of organic-based flexible displays using an amorphous IZO anode grown at room temperature. The IZO anode films were grown by a conventional DC reactive sputtering on the polycarbonate (PC) substrate at room temperature using a synthesized IZO target in a ambient. Both x-ray diffraction (XRD) and high resolution electron microscope (HREM) examination results show that the IZO anode film grown at room temperature Is complete amorphous structure due to low substrate temperature. A sheet resistance of , average transmittance above 90 % in visible range, and root mean spare roughness of were obtained even in the IZO anode film grown on PC substrate at room temperature. It is shown that the doped flexible organic light emitting diode (OLED) fabricated on the IZO anode exhibit comparable current-voltage-luminance characteristics as well as external quantum efficiency and power efficiency to OLED fabricated on conventional ITO/Glass substrate. These findings indicate that the IZO anode film grown on PC substrate is a promising anode materials for the fabrication of organic based flexible displays.

Mechanical properties of stainless steel composites with titanium carbonitride consolidated by spark plasma sintering

In this paper, stainless steel–titanium carbonitride-based composites were fabricated and analyzed to utilize for bipolar plate in fuel cells. In order to study the size effect of titanium carbonitride on the mechanical and corrosion resistance properties of the composites, micro and nanosize titanium carbonitride powders were used. Stainless steel–carbonitride composites were prepared by spark plasma sintering and subsequently annealed at different temperatures up to 1100℃ to improve the morphological and mechanical properties. Various properties of the obtained samples were compared before and after annealing. It was shown that after heat treatment, the mechanical properties of the stainless steel–carbonitride composites improved due to the diffusion of titanium carbonitride particles into stainless steel. Addition of microsized titanium carbonitride powders was found to be effective to improve the mechanical properties, such as microhardness and compressive strength, of the composite. However, addition of nanosized titanium carbonitride powders led to an increase of corrosion resistivity of the composite. Physical properties, such as thermal and chemical stability of the obtained composite samples were investigated by microhardness tester, potentiostat, field emission-scanning electron microscope, EDX and X-ray diffraction.

Synthesis, Characterization and Functionalization of the Coated Iron Oxide Nanostructures

The iron oxides nanoparticles and iron oxide with other compounds are of importance in fields including biomedicine, clinical and bio-sensing applications, corrosion resistance, and magnetic properties of materials, catalyst, and geochemical processes etc. In this work we describe the preparation and investigation of the properties of coated magnetic nanoparticles consisting of the iron oxide core and organic modification of the residue. These fine iron oxide nanoparticles were prepared in air environment by the co-precipitation method using of Fe 2+ : Fe 3+ where chemical pre- cipitation was achieved by adding ammonia aqueous solution with vigorous stirring. During the synthesis of nanoparti- cles with a narrow size distribution, the techniques of separation and powdering of nanoparticles into rather monodisperse fractions are observed. This is done using controlled precipitation of particles from surfactant stabilized solutions in the form organic components. It is desirable to maintain the particle size within pH range, temperature, solution ratio wherein the particle growth is held at a minimum. The iron oxide nanoparticles can be well dispersed in an aqueous solution were prepared by the mentioned co-precipitation method. Besides the iron oxide nanowires were prepared by using similar method. These iron oxide nanoparticles and nanowires have controlled average size and the obtained products were investigated by X-ray diffraction, FESEM and other methods.

Comparison Characteristic of Large Area Graphene Films Grown by Chemical Vapor Deposition with Nano-Graphite Structures

an attractive material for a wide variety of applications in nano-electronic. Various techniques have been developed to produce graphene to realize its potential applications. Chemical vapor deposition (CVD) of graphene films on Cu substrate is a primary technique for high quality graphene synthesis. In this work we demonstrate the growth of large area graphene layers by chemical vapor deposition (CVD) on copper substrates. Graphene growth was achieved by the flow of methane and hydrogen gasses over a copper thin film acting as catalyst at ambient pressure. Optimal growth conditions were found by varying the different parameters. A transfer process was carried out through treatment with a nickel etchant solution to isolate the graphene with using polymer bond for placement on an oxidized silicon substrate. Transfer methods are essential for effective optical contrast and SEM microscopy measurements. Characterization was performed with optical microscopy, Raman spectroscopy, XRD, SEM and other to determine the quality of layers.

Morphology Control of ZnO Nanorods on ITO Substrates in Solution Processes

We report growth of vertically well-aligned zinc oxide (ZnO) nanorods on indium-tin oxide (ITO)/glass substrates using a simple aqueous solution method at low temperature via control of the ZnO seed layer morphology. ZnO nanoparticles acting as seeds are pre-coated on ITO-coated glass substrates. by spin coating to control distribution and density of the ZnO seed nanoparticles. ZnO nanorods were synthesized on the seed-coated substrates in a dipping process into a main growth solution. It was found that the alignment of ZnO nanorods can be effectively manipulated by the spin-coating speed of the seed layer. A grazing incidence X-ray diffraction pattern shows that the ZnO seed layer prepared using the higher spin-coating speed is of uniform seed distribution and a flat surface, resulting in the vertical growth of ZnO nanorods aligned toward the [0001] direction in the main growth process.

Growth of ZnO Nanostructures on Various Substrates by Simple Aqueous Solution Method

Growth of well-aligned ZnO nanostructures on various substrates such as GaN, ITO/glass, and sapphire was realized via a simple aqueous solution method at low temperature of . Morphology of ZnO nanostructures grown on various substrates as function of substrate was studied. It was found that ZnO nanostructures is a strong function of substrate. It was clearly observed that the morphology of ZnO nanostructures could be varied by change of substrate. Morphology, crystallinity, and crystal characteristics were carried out by FE-SEM, synchrotron x-ray scattering measurements, and high-resolution electron microscopy, respectively.

Characteristics of Fluorescent Organic Light Emitting Diodes using Amorphous IZO Anode Film

We reported on characteristics of the fluorescent OLED fabricated on commercial ITO/glass and BCS grown IZO/glass substrate, respectively. The amorphous IZO anode film grown by box cathode sputtering(BCS) exhibited similar electrical and optical characteristics to commercial ITO anode even though it was deposited at room temperature. In addition, the amorphous IZO anode showed higher workfunction (5.2 eV) than that of the commercial ITO anode (5.0 eV) after ozone treatment for 10 min. Furthermore, fluorescent OLED fabricated on amorphous IZO anode film showed improved current-voltage-luminance characteristics, external quantum efficiency and power efficiency en contrast with fluorescent OLED fabricated on commercial ITO anode film. It was thought that smooth surface and high workfunction of amorphous IZO anode lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers.