• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.314-314
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• 2012

The dilute magnetic semiconductors (DMS) have been developed to multi-functional electro-magnetic devices. Specially, the Si based DMS formed by ion implantation have strong advantages to improve magnetic properties because of the controllable effects of carrier concentration on ferromagnetism. In this study, we investigated the deep level states of Fe- and Co-ions implanted Si wafer during rapid thermal annealing (RTA) process. The p-type Si (100) wafers with hole concentration of $1{\times}10^{16}cm^{-3}$ were uniformly implanted by Fe and Co ions at a dose of $1{\times}10^{16}cm^{-2}$ with an energy of 60 keV. After RTA process at temperature ranges of $500{\sim}900^{\circ}C$ for 5 min in nitrogen ambient, the Au electrodes with thickness of 100 nm were deposited to fabricate a Schottky contact by thermal evaporator. The surface morphology, the crystal structure, and the defect state for Fe- and Co- ion implanted p-type Si wafers were investigated by an atomic force microscopy, a x-ray diffraction, and a deep level transient spectroscopy, respectively. Finally, we will discuss the physical relationship between the electrical properties and the variation of defect states for Fe- and Co-ions implanted Si wafer after RTA.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.480-480
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• 2011

양극산화(anodization)는 금속을 전기화학적으로 산화시켜 금속산화물로 만드는 기술로서 최근 다양한 크기의 나노 구조를 제조하는 기술로 각광받고 있으며, 이러한 기술에 의하여 얻어지는 anodic aluminum oxide(AAO)는 magnetic data storage, optoelectronic device, sensor에 적용될 수 있는 nano device 뿐만 아니라 nanostructure를 제조하기 위한 template 및 mask로써 최근 광범위 하게 연구되고 있다. 또한, AAO는 Al2O3의 단단한 구조를 가진 무기재료이므로 solid mask로써 다른 porous materials 보다 뛰어난 특성을 갖고 있다. 또한 electron-beam lithography 및 block co-polymer 에 의한 patterning 과 비교하여 매우 경제적이며, 재현성이 우수할 뿐만 아니라 대면적에서 나노 구조의 크기 및 형상제어가 비교적 쉽기 때문에 널리 사용되고 있다. 그러나, AAO 형성 시 생기게 되는 반구형 모양의 barrier layer는 물질(substance)과 기판과의 direct physical and electrical contact을 방해하기 때문에 해결해야 할 가장 큰 문제점 중 하나로 알려져 있다. 따라서 본 연구에서는 실리콘 기판위의 형성된 AAO의 barrier layer를 Cl/BCl3 gas mixture에서 Neutral Beam Etching (NBE)과 Ion Beam Etching (IBE) 로 각각 식각한 후 그 결과와 비교하였다. NBE와 IBE 모두 Cl2/BCl3 gas mixture에서 BCl3 gas의 첨가량이 60% 일 경우 etch rate이 가장 높게 나타났고, optical emission spectroscopy (OES)로 Cl2/BCl3 플라즈마 내의 Cl radical density와 X-ray photoelectron spectroscopy (XPS)로 AAO 표면 위를 관찰한 결과 휘발성 BOxCly의 형성이 AAO 식각에 크게 관여함을 확인 할 수 있었다. 또한, NBE와 IBE 실험한 다양한 Cl2/BCl3 gas mixture ratio 에서 AAO가 식각이 되지만, 이온빔의 경우 나노사이즈의 AAO pore의 charging에 의해 pore 아래쪽의 위치한 barrier layer를 어떤 식각조건에서도 제거하지 못하였다. 하지만, NBE에서는 BCl3-rich Cl2/BCl3 gas mixture인 식각조건에서 AAO pore에 휘발성 BOxCly를 형성하면서 barrier layer를 제거할 수 있었다.

• Analytical Science and Technology
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• v.12 no.3
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• pp.218-223
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• 1999

A single use, screen-printed sensor for the measurement of liquid phase ethanol was developed and its electrochemical performance was investigated. Disposable type edthanol sensor was fabricated by serially screen printing the carbon paste, silverd pasted and insulator inlon a polyester substrate to pattern working and reference electrode sites and electrical contact. Alcohol dehydrogenase(ADH) or alcohol oxidase(AOD) together with appropriate electron transfer mediators was immobilized on the working electrode. To improve the sensitivity and reproducibility of carbon paste electrode, some pretreatment procedures were applied and their resultant electrochemical performance was examined. The disposable type electrochemical ethanol sensor developed in this study conveniently determines the ethanol in liquid samples such as blood and in fermentation process.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.21-25
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• 2014

In order to develop 2nd generation (2G) high-temperature superconducting (HTS) wires as commercial products, it is necessary to perform a high speed investigation of their superconducting performance. Room-temperature and non-contact optical scanning tools are necessary to verify the microstructure of the superconducting materials, the current flow below the critical temperature, and the critical current density. In this paper, we report our results of an inspection of the electrical transport properties of coated conductors. The samples that we used in our study were highly qualified rare-earth based coated conductors produced via co-evaporation, and $SmBa_2Cu_3O_{7-y}$ (SmBCO) was the superconducting materials used in our studies. A film grown on IBAD-MgO templates shows larger than 400 A/cm at 77 K and a self-field. The local transport properties of the films were investigated by room-temperature imaging by thermal heating. The room-temperature images show structural inhomogeneities on the surface of the films. Bolometric response imaging via low-temperature bolometric microscopy was used to construct the local current mapping at the surface. These results indicate that the non-uniform regions on the surface disturb the current flow, and laser scanning images at room-temperature and at a low-temperature suggest a correlation between the structural properties and transport properties. Thus this method can be effective to evaluate the quality of the coated conductors.

• Polymer(Korea)
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• v.37 no.2
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• pp.184-195
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• 2013

Acrylic pressure sensitive adhesive (PSA) tapes were used for the automotive, the electrical and the electronic industries and the display module junction. In this study, the manufacture of high-strength structural tape used 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AAC), and UV irradiation for photo-polymerization, and the semi-structural properties of acrylic PSA tape with the AAC content and inorganic filler $SiO_2$ content were investigated. The initial adhesion strength was lowered by the rigidity of molecule chains due to the use of AAC, and the adhesion strength increased with increasing wetting time. The wetability, contact angle, and SEM images of PSA tapes with various contents of AAC were determined. Without filler, the peel strength and dynamic shear strength of PSA tape showed inverse correlation but the peel strength and dynamic shear strength increased with increasing filler content. From these correlations the PSA tapes could be optimized for the applications requiring high performance.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.447-453
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• 2013

Since PSDs(Platform Screen Doors) are set up at many subway stations, their design related to safety has become gradually important. In particular, the interference check with a running railway vehicle is the most important of performance indices because the collision between PSDs and vehicles can be dangerous for passengers in the car and on platforms. When the train comes into a station with a curvature, the passenger car has a large translational and rotational motion and the displacement is enough for coming in contact with PSD. The performance is affected by many design parameters such as rail design parameters and vehicle velocity. This study proposes dynamic analysis models for railway vehicles and rails. Some parameters were also considered in the models to determine their influence on the performance.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.663-669
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• 2009

In the electrical railway, the increase of tensions in an overhead contact lines is essential to speed-up of train, because current collection quality largely depends on the ratio of a wave propagation speed to a train speed. For Kyungbu high-speed line, a pulley-type tensioning device is required to have a tension variation of maximum 3%. Therefore we developed a pulley-type tensioning device in order to meet tension variation requirement of the high-speed tensioning device. To verify the performance of the developed device, a performance test, overload test and failure test were carried out according to the factory test procedure of the Kyung-Bu High-speed line. Furthermore, we also performed reliability performance through not only a fatigue test in a factory, but also on-line verification test in Chungbuk line for over 1 year. These tests verified that the tensioning device had applicability to a main line.

• Korean Journal of Materials Research
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• v.19 no.8
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• pp.452-456
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• 2009

In high-efficiency Cu(In,Ga)$Se_2$ solar cells, Na is doped into a Cu(In,Ga)$Se_2$ light-absorbing layer from sodalime-glass substrate through Mo back-contact layer, resulting in an increase of device performance. However, this supply of sodium is limited when the process temperature is too low or when a substrate does not supply Na. This limitation can be overcome by supplying Na through external doping. For Na doping, an NaF interlayer was deposited on Mo/glass substrate. A Cu(In,Ga)$Se_2$ absorber layer was deposited on the NaF interlayer by a three-stage co-evaporation process As the thickness of NaF interlayer increased, smaller grain sizes were obtained. The resistivity of the NaF-doped CIGS film was of the order of $10^3{\Omega}{\cdot}cm$ indicating that doping was not very effective. However, highest conversion efficiency of 14.2% was obtained when the NaF thickness was 25 nm, suggesting that Na doping using an NaF interlayer is one of the possible methods for external doping.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.2
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• pp.75-82
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• 2017

In this paper, we consider social network analysis that focuses on community detection. Social networks embed community structure characteristics, i.e., a society can be partitioned into many social groups of individuals, with dense intra-group connections and much sparser inter-group connections. Exploring the community structure allows predicting as well as understanding individual's behaviors and interactions between people. In this paper, based on the interaction information extracted from a real-life Bluetooth contacts, we aim to reveal the social groups in a society of mobile carriers. Focusing on estimating the closeness of relationships between network entities through different similarity measurement methods, we introduce the clustering scheme to determine the underlying social structure. To evaluate our community detection method, we present the evaluation mechanism based on the basic properties of friendship.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.5 s.347
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• pp.25-33
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• 2006

We have extracted the material parameters such as absorption coefficients of GaN, $Al_{0.2}Ga_{0.8}N$, and Schottky contact metal Ni of Schottky Diode UV-A and B detectors using a transfer matrix method (TMM). The ratios of the absorbed light to the total incident amount at the depletion regions of GaN and $Al_{0.2}Ga_{0.8}N$ have been calculated in order to obtain the spectral responsivity. Absorption coefficients of the materials have been obtained by fitting the simulated data with measured data. The depletion layer thickness has been obtanied by capacitance-voltage measurement. The results pave the way for the optimum design of UV Schottky detectors. Since the absorption coefficient of the Ni electrode is very high, its thickness is a major factor that determines the responsivity. It is possible to attain improved UV detectors using thinnest possible Ni electrodes and wide depletion regions of GaN and $Al_{0.2}Ga_{0.8}N$.