Yong Woo Kim

Behavior characteristics of nano-stage according to hinge structure.

Nano-stages are used in many ultra-precision systems, such as scanning probe microscope (SPM), optical fiber aligners, ultra-precision cutting, measuring and optical systems. Generally, ultra-precision machining and measuring are achieved using a nano-scale motion stage actuated using Piezo-electric actuators (PZT), and the importance of and demands for the motion stage increase with the need to improve system performance and accuracy. However, it is difficult to find solutions because the performance and characteristics of nano-scale motion stages are determined by various factors, such as the hinge structure, actuator, and method of system control. This paper focuses on improving of leafspring and planar joint hinges, and suggests a composite joint hinge stage.

Development of a high-efficiency laminated dye-sensitized solar cell with a condenser lens.

Dye-sensitized solar cells have slightly lower photoelectric efficiency than silicon solar cells. Researchers have investigated various ways to address this problem. In this paper, we found that the optimized separation between the condenser lens and the cells was 8 mm. The cell efficiency increased from 2.5% to 8.3% compared to two isolated cells without a lens. If the efficiency of the basic cell can be increased sufficiently, it should be possible to commercialize the product.

Surface patterning for brittle amorphous material using nanoindenter-based mechanochemical nanofabrication

This paper demonstrates a micro/nanoscale surface patterning technology for brittle material using mechanical and chemical processes. Fused silica was scratched with a Berkovich tip under various normal loads from several mN to several tens of mN with various tip rotations. The scratched substrate was then chemically etched in hydrofluoric solution to evaluate the chemical properties of the different deformed layers produced under various mechanical scratching conditions. Our results showed that either protruding or depressed patterns could be generated on the scratched surface after chemical etching by controlling the tip rotation, the normal load and the etching condition. In addition, the mask effect of amorphous material after mechanical scratching was controlled by conventional mechanical machining conditions such as contact area, chip formation, plastic flow and material removal.

Evaluation of characteristics for dye-sensitized solar cell with reflector applied

Dye-sensitized solar cells have slightly lower photoelectric efficiency than silicon solar cells. Researchers have investigated various ways to address this problem. This study improved the efficiency of a dye-sensitized solar cell by re-driving it with a reflector, reusing discarded light after it was absorbed. The reflector increased efficiency by about 50%, by increasing the size of the pattern shape and increasing the distance of the reflector.

A Study on the Lubrication Characteristics of the Hydro-Static Journal Bearing for a Crank Shaft Pin Turner by Applying Dimple

1 부산대학교 나노융합기술학과 (Department of Nanofusion Technology, Pusan National Univ.)2 부산대학교 나노메카트로닉스공학과 (Department of Nanomechatronics Engineering, Pusan National Univ.) 3 삼성테크윈㈜ (Samsung Techwin)4 부산대학교 설계기반미래성형기술센터 (Center of Innovative Technology on Advanced Forming, Pusan National Univ.) Corresponding author: dwoolee@pusan.ac.kr, Tel: +82-51-510-3129

Development of Dye-Sensitized Solar Cell for High Conversion Efficiency

The Solar cell energy is presently promising because of oil inflation, fuel exhaustion, global warming, and space development. Many advanced countries rapidly develop the solar cell energy under a nation enterprise. Particularly, dye-sensitized solar cell (DSC), the 3rd generation solar cell, has low-cost of manufactures about 1/3~1/5 times compared with the silicon solar cell, which encourages the research globally. Dye-sensitized Solar Cell (DSC) is evaluated to be low-cost technology as the manufacturing DSC is more inexpensive 5 times than producing Silicon Solar Cell. Currently, the best conversion efficiency is 11%, the tile-shaped modules are being produced in STI, Austria. Moreover the efficiency to increase over 15% and the process of fabricating DSC for commercialization are attempted to be highly researched. Recently, production of nano-particles becomes available due to development of nanotechnologies. Since they have broad contact area comparing to the existing compound materials being generally used and increased mechanical, thermal and electrical characteristics, etc., they are attracting public attention as a new material to implement various functions. Especially, nano-tube has more excellent mechanical and electrical characteristics than normal particle type materials. And it is known that the smaller its diameter, i.e. aspect ratio, is, the better its characteristics are. Accordingly a lot of researches related to nano-compound materials have been being progressed nationally and internationally (Gojny et al., 2003; Jijima, 1991; Chang et al., 2001). It is new methods to improve light conversion efficiency using several approaches such as nanocrystalline CNT/TiO2 hybrid material, reflect mirror with micro pyramid structure, and concentrating light with Fresnel lens. Figure.1 shows the operational principle and structure of dye sensitized cell. If visible rays are absorbed by n-type nano particles TiO2 that dye molecules are chemically absorbed on the surface, the dye molecules generate electron-hole pairs, and the electron were injected into the conduction band of semiconductor’s oxides. These electrons that are injected into the semiconductor’s oxide electrode generate current through each nano particles’ interfaces. The holes that are made from dye molecules are deoxidized by receiving electrons, thus causing the dye-sensitized cells begin to work (Zhang et al., 2010).

A Study of Photocatalyst of the TiO2 Thin Film with Acid Dispersed CNT for Dye-Sensitized Solar Cell

M-CNTs (Multiwall Carbon Nano Tubes) can be used as an electrode, transferring electrons and heat very easily. This property helps transfer electrons created in TiO2 layer of DSSC (Dye-sensitized Solar Cell). CNTs layer with TiO2 utilized for the photocatalyst is expected to contribute to improve the efficiency of the solar cell. The Photocatalyst of TiO2 thin film was manufactured from titanium isopropoxide, ethanol, and HCl by a sol-gel process. To determine the property of TiO2 thin film with CNT, we performed to mix acid dispersed CNT in TiO2 Sol-gel and make coating membranes using sol-gel with different densities of CNT. It was found that the crystal structure changed from the anatase phase to the rutile phase having higher efficiency by XRD measure after treatment of high temperature sintering. To demonstrate the property of each sample, the transmittance of the TiO2 thin film was measured by a spectrometer and dispersion of CNT of the thin film was measured by SEM. In conclusion, the capacitance as the parameter which can affect performance of DSSC was investigated.

Characteristics of machined surface controlled by cutting tools and conditions in machining of brittle material

Abstract One of the ultra-precision machining methods was adapted for brittle material as well as soft material by using multi-arrayed diamond tips and high speed spindle. Conventional machining method is too hard to control surface roughness and surface texture against brittle material because the particles of grinding tools are irregular size and material can be fragile. Therefore, we were able to design tool paths and machine controlled pattern on surface by multi-arrayed diamond tips with uniform size made in MEMS fabrication and high speed spindle, and the maximum speed was about 3 × 10 5 r/min. We defined several parameters that can affect the machining surface. Those were multi-array of diamond tips ( n × n ), speed of air spindle and feeding rate. The surface roughness and surface texture can be controlled by those parameters for micro machining.

Fabrication of Micro Tetrahedron Patterns Using Ultra-Precision Shaping System

Recently, ultra-precision machining of components and dies for information and communication industries, such as fresnel mirrors, diffraction lens, and die for super high intensity reflective sheet is one of the major target. To machine three-dimensional micro patterns, such as super high-intensity reflective sheets, ultra-precision and mirror surface fabrication processes are required. It has been reported, however, that continuous cutting, such as turning or shaping, is more suitable to ultra-precision machining. Many researchers have studied the manufacturing process of reflective sheet dies to obtain high form accuracy and surface quality. In this paper, ultra-precision shaping system was developed to fabricate micro patterns mechanically. In order to estimate performance of the shaping system, micro V-shaped grooves and tetrahedron pattern arrays for a super high intensity reflective sheet was applied. Also, a new measuring technology to inspect form and machining errors of a machined tetrahedron patterns was proposed. The results show that shaping system has a positioning accuracy of x, y, z axis with 100, 10, 10nm resolution, respectively. Micro V-shaped grooves could be machined at various depths and micro tetrahedron patterns with a good quality were obtained as well.