• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.208-208
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• 2010

Zinc oxide (ZnO) is a functional material with interesting optical and electrical properties, a wide band gap (more than 3.3 eV), a high transmittance in the visible light region, piezoelectric properties, and a high n-type conductivity. This material has been investigated for use in many applications, such as transparent electrodes, blue light-emitting diodes, and ultra-violet detector. ZnO films grown under low oxygen pressure by thin film deposition methods show low resistivity and large free electron concentration. Therefore, reducing the background carrier concentration in ZnO films is one of the major challenges ahead of realizing high-performance ZnO-based optoelectronic devices. In this study, we deposited ZnO thin films on sapphire substrates by pulsed laser deposition (PLD) with employing an oxygen plasma source to decrease the background free-electron concentration and enhance the crystalline quality. Then, the substrate temperature was varied between 200 'C to 900 'C The vacuum chamber was initially evacuated to a pressure of $10^{-6}$ Torr, and then a pure $O_2$ gas was introduced into the chamber and the pressure during deposition was maintained at $10^{-2}$ Torr. Crystallinity and orientation of ZnO films were investigated by X-ray diffraction (XRD). The film surface was analyzed with atomic force microscope (AFM). And electrical properties were measured at room temperature by Hall measurement.

• Current Photovoltaic Research
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• v.2 no.2
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• pp.59-62
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• 2014

Minority carrier diffusion length is one of the most important parameters of solar cells, especially for short circuit current density (Jsc). In this report, we proposed the calculating method of the minority carrier diffusion length ($L_n$) in CIGS solar cells through biased quantum efficiency (QE). To verify this method's reliability, we chose two CIGS samples which have different grain size and calculated $L_n$ for each sample. First of all, we calculated out that $L_n$ was 56nm and 97nm for small and large grain sized-cell through this method, respectively. Second, we found out the large grain sized-cell has about 7 times lower defect density than the small grain sized-cell using drive level capacitance profiling (DLCP) method. Consequently, we confirmed that $L_n$ was mainly affected by the micro-structure and defect density of CIGS layer, and could explain the cause of Jsc difference between two samples having same band gap.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.384-389
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• 2009

ZnO, a wurtzite lattice structure, has attracted much attention as a promising material for light-emitting diodes (LEDs) due to highly efficient UV emission resulting from its large band gap of 3.37 eV, large exciton binding energy of 60 meV, and low power threshold for optical pumping at room temperature. For the realization of LEDs, both n-type ZnO and p-type ZnO are required. Now, n-type ZnO for practical applications is available; however, p-type ZnO still has many drawbacks. In this study, ZnO films were grown on glass substrates by using atomic layer deposition (ALD) and the ZnO films were irradiated by nitrogen ion beams (20 keV, $10^{13}{\sim}10^{15}ions/cm^2$). The effects of nitrogen-beam irradiation on the ZnO structure as well as the electrical property were investigated by using fieldemission scanning electron microscopy (FESEM) and Hall-effect measurement.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.105-105
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• 2011

ZnO is a promising material since it could be applied to many fields such as solar cells, laser diodes, thin films transistors and gas sensors. ZnO has a wide and direct band gap for about 3.37 eV at room temperature and a high exciton binding energy of 60 meV. In particular, ZnO features high sensitivity to toxic and combustible gas such as CO, NOX, so on. The development of gas sensors to monitor the toxic and combustible gases is imperative due to the concerns for enviromental pollution and the safety requirements for the industry. In this study, we investigated the effect of substrate temperature and post-annealing on structural and electrical properties of ZnO thin films. ZnO thin films were deposited by pulsed laser deposition (PLD) at various temperatures at from room temperature to $600^{\circ}C$. After that, post-annealing were performed at $600^{\circ}C$. To inspect the structural properties of the deposited ZnO thin films, X-ray diffraction (XRD) was carried out. For gas sensors, the morphology of the films is dominant factor since it is deeply related with the film surface area. Therefore, the atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) were used to observe the surface of the ZnO thin films. Furthermore, we analyzed the electrical properties by using a Hall measurement system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2770-2776
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• 2015

The development of efficient wearable antennas is required to implement short range body-centric wireless communication links for various internet of thing applications. We present simulation and measurement results of conductive-fiber-based wearable antennas which can comfortably fabricated directly on usual clothing materials. The proposed antenna is a form of a rectangular patch antenna designed by weaving conductive fibers on a felt substrate. A full-wave electromagnetic simulation tool is used to investigate the antenna performance such as antenna impedance, resonant frequency, and radiation efficiency. Parametric studies show that the radiation efficiency increases from 67.5% to 70.4% by widening the gap between conductive fibers from 0.25mm to 3mm. This implies a wearable antenna with good radiation efficiency can be designed despite of less portion of conductive fibers on the antenna. The simulation results are also verified by measured results with fabricated antennas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.10
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• pp.5115-5122
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• 2013

This paper has studied about the development and application of landslide collapse prediction real-time monitoring system based on USN to detect and measure the collapse of landslide. The rainfall measuring sensor, gap water pressure sensor, indicator displacement measuring sensor, index inclination sensor, water content sensor and image analysis sensor are selected and these are applied on the test bed. Each sensor's operation and performance for reliability verification is tested by the instrument which is installed in the field. As the result, u-IT based real-time landslide monitoring system which is developed by this research for landslide collapse detection could minimize life and property damages because it makes advance evacuation with collapse risk pre-estimate through real-time monitoring on roadside cut and bedrock slopes. This system is based on the results of this study demonstrate the effect escarpment plan are spread throughout.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.83-92
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• 2005

An electromagnetic acoustic transducer (EMAT) is a unique probe that does not require a couplant or gel and also can usually generate or detect an ultrasonic wave into specimens across a small gap. It, therefore can be applied in a noncontact mode with a high degree of reproducibility. Especially stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates. It is very important to evaluate the layup errors in prepreg laminates. A nondestructive technique can therefore serve as a useful measurement for detecting layup errors. This shear wave for detecting the presence of the errors is very sensitive. A decomposition model has been used in the interpretation and prediction of test results. Test results have been com pared with model data. It is found that the high probability shows between tests and the model utilized in characterizing cured layups of the laminates. Also a C-scan method was used for detecting layup of the laminates because of extracting fiber orientation information from the ultrasonic reflection caused by structural imperfections in the laminates. Therefore, it was found that interface C-scan images show the fiber orientation information by using two-dimensional fast Fourier transform (2-D FFT).

• The Journal of the Acoustical Society of Korea
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• v.24 no.4
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• pp.194-201
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• 2005

Since the necessity for the accurate measurement in the field of acoustics, vibration, and ultrasound was internationally increased, CCAUV (Consultative Committee for Acoustics , Ultrasound and Vibration) was created by the CIPM (International Committee for Weights and Measures) in 1998. One of the first activities of CCAUV is the key comparison on 1' standard microphones. The key comparison was done from April. 1999 to April. 2001 and 12 NMIs(National Metrology Institutes) including KRISS (Korea Research Institute of Standards and Science) were participated. The pilot laboratory was the National Physical Laboratory(NPL). The traveling standards were two LSIP(Laboratory Standard 1' Pressure Type) microphones specified in IEC 61094-1 and the calibration frequency ranges covers from 63Hz to 8kHz. In this paper, the analyzed results in the final report were summarized.

• Journal of Digital Convergence
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• v.11 no.3
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• pp.41-48
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• 2013

Emerging three-dimensional television (3DTV) as a new IT product shows a possibility that television is not for just watching broadcasting, but an attractive tool for applying it to our real life. Three dimensional television is generally more effective and attractive than two-dimensional television (2DTV). But it still needs continuous technological improvement to solve its inherent limitations until many customers decide to purchase 3DTVs without hesitation. Innovative products like 3DTV encounter a quality problem leading purchase decision by customers. Quality is regarded as one of the most important factors affecting customers to adopt and use the product. Furthermore, measuring quality effectively is considerable for the 3DTV research. In this paper, we suggest the Analytic Hierarchy Process(AHP) method for evaluating 3DTVs in a view of quality. We describe quality criteria affecting the 3DTV selection through a literature survey and develope an analytical method for measuring quality. We classify the quality of 3DTV into four types and suggest a concept of the quality ratio as a measurement criteria instead of the quality gap. Though a numerical example, we show how priorities of 3DTV with versatile manufacturers is computed.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.847-858
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• 2016

An overview is given on the work of the Laboratory of Nuclear Energy Systems at ETH, Zurich (ETHZ) and of the Laboratory of Thermal Hydraulics at Paul Scherrer Institute (PSI), Switzerland on tight-lattice bundles. Two-phase flow in subchannels of a tight triangular lattice was studied experimentally and by computational fluid dynamics simulations. Two adiabatic facilities were used: (1) a vertical channel modeling a pair of neighboring sub-channels; and (2) an arrangement of four subchannels with one subchannel in the center. The first geometry was equipped with two electrical film sensors placed on opposing rod surfaces forming the subchannel gap. They recorded 2D liquid film thickness distributions on a domain of $16{\times}64$ measuring points each, with a time resolution of 10 kHz. In the bubbly and slug flow regime, information on the bubble size, shape, and velocity and the residual liquid film thickness underneath the bubbles were obtained. The second channel was investigated using cold neutron tomography, which allowed the measurement of average liquid film profiles showing the effect of spacer grids with vanes. The results were reproduced by large eddy simulation + volume of fluid. In the outlook, a novel nonadiabatic subchannel experiment is introduced that can be driven to steady-state dryout. A refrigerant is heated by a heavy water circuit, which allows the application of cold neutron tomography.