• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.297.2-297.2
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• 2013

Scavenging electricity from wasteful energy resources is currently an important issue and piezoelectric nanogenerators (NGs) based on zinc oxide (ZnO) are promising energy harvesters that can be adapted to various portable, wearable, self-powered electronic devices. Although ZnO has several advantages for NGs, the piezoelectric semiconductor material ZnO generate an intrinsic piezoelectric potential of a few volts as a result of its mechanical deformation. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. Oxygen vacancies (Vo) that work as donors exist in ZnO thin film and usually screen some parts of the piezoelectric potential. Consequently, the ZnO NGs' piezoelectric power cannot reach to its theoretical value, and thus decreasing the effect from Vo is essential. In the present study, c-axis oriented insulator-like sputtered ZnO thin films were grown in various temperatures to fabricate an optimized nanogenerator (NGs). The purity and crystalinity of ZnO were investigated with photoluminescence (PL). Moreover, by introducing a p-type polymer usually used in organic solar cell, it was discussed how piezoelectric passivation effect works in ZnO thin films having different types of defects. Prepared ZnO thin films have both Zn vacancies (accepter like) and oxygen vacancies (donor like). It generates output voltage 20 time lager than n-type dominant semiconducting ZnO thin film without p-type polymer conjugating. The enhancement is due to the internal accepter like point defects, zinc vacancies (VZn). When the more VZn concentration increases, the more chances to prevent piezoelectric potential screening effects are occurred, consequently, the output voltage is enhanced. Moreover, by passivating remained effective oxygen vacancies by p-type polymers, we demonstrated further power enhancement.

• Korean Journal of Materials Research
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• v.34 no.2
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• pp.111-115
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• 2024

Silicon carbide (SiC) has emerged as a promising material for next-generation power semiconductor materials, due to its high thermal conductivity and high critical electric field (~3 MV/cm) with a wide bandgap of 3.3 eV. This permits SiC devices to operate at lower on-resistance and higher breakdown voltage. However, to improve device performance, advanced research is still needed to reduce point defects in the SiC epitaxial layer. This work investigated the electrical characteristics and defect properties using DLTS analysis. Four deep level defects generated by the implantation process and during epitaxial layer growth were detected. Trap parameters such as energy level, capture-cross section, trap density were obtained from an Arrhenius plot. To investigate the impact of defects on the device, a 2D TCAD simulation was conducted using the same device structure, and the extracted defect parameters were added to confirm electrical characteristics. The degradation of device performance such as an increase in on-resistance by adding trap parameters was confirmed.

• Journal of Sensor Science and Technology
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• v.23 no.1
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• pp.51-57
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• 2014

The evaporating materials for $MgGa_2Se_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $MgGa_2Se_4$ compounded polycrystal powder was deposited on thoroughly etched semi-insulated GaAs(100) substrate by the hot wall epitaxy (HWE) method system. The source and substrate temperatures of optimized growth conditions, were $610^{\circ}C$ and $400^{\circ}C$, respectively.The source and substrate temperatures were $610^{\circ}C$ and $400^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the $MgGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=2.34\;eV-(8.81{\times}10^{-4}\;eV/K)T^2/(T+251\;K)$. After the as-grown $MgGa_2Se_4$ single crystal thin films was annealed in Mg-, Se-, and Ga-atmospheres, the origin of point defects of $MgGa_2Se_4$ single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of $V_{Mg}$, $V_{Se}$ obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Se-atmosphere converted $MgGa_2Se_4$ single crystal thin films to an optical n-type. Also, we confirmed that Ga in $MgGa_2Se_4$/GaAs did not form the native defects because Ga in $MgGa_2Se_4$ single crystal thin films existed in the form of stable bonds.

• Archives of Reconstructive Microsurgery
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• v.18 no.2
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• pp.62-66
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• 2009

Purpose: Despite the free tissue transfer using microsurgical technique being the current trend of soft tissue reconstruction of the hand, the pedicled groin flap has the advantage to provide coverage for the mangled hand without necessitating the use of a damaged arterial system and also providing the benefit of saving the arterial system for later free tissue transfer. This report presents the author's experience using pedicled groin flap in four cases of mangled hands with massive bone and soft tissue defects requiring later thumb reconstruction with the free wrap around flap. Materials and methods: The patients' age ranged from 30 to 51 years; three patients were male and one was female. The causes of mangled hand included two machinery crush injuries, one laboratory explosion and one motor vehicle accident. While evaluating the post-operative results, factors like flap survival, complications, stability in opposition, pinch power and 2 point discrimination were taken into account. Results: All massive soft tissue defects of the hands were completely covered with pedicled groin flap successfully. The reconstructed thumb using free wrap around flap did not have any limitation in opposition. There was no occurrence of post-operative infection and all the flaps survived completely. The average pinch power was 70% of the contralateral intact thumb and average 2 point discrimination was 10 mm. Conclusion: The pedicled groin flap for the reconstruction of the massive soft tissue defects of the hand with subsequent reconstruction of the thumb with a wrap around flap is a very useful procedure. The combined use of pedicled groin flap and wrap around flap allows adequate coverage of sizable soft tissue defects and functional thumb opposition in cases of reconstruction of the mangled hands.

• Archives of Plastic Surgery
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• v.36 no.5
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• pp.605-610
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• 2009

Purpose: Substantial tissue necrosis after snake bites requiring coverage with flap surgery is extremely rare. In this article, we report 7 cases of soft tissue defects in the upper and the lower extremities caused by snake bites, which needed to be covered with flaps. Among the vast mass of publications on snake bites there has been no report that focuses on flap coverage of soft tissue defects due to snake bite sequelae. Methods: Seven cases of soft tissue defects with tendon, ligament, or bone exposure after snake bites were included. All patients were males without comorbidities, the average age was 35 years. All of them required coverage with a flap. In 6 cases, the defect was localized on the upper extremity, in one case the lesion was on the lower extremity. Local flaps were used in 6 cases, one case was covered with a free flap. The surgical procedures included one kite flap, one cross finger flap and digital nerve reconstruction with a sural nerve graft, one reverse proximal phalanx island flap, one groin flap, one adipofascial flap, one neurovascular island flap, and one anterolateral thigh free flap. The average interval from injury to flap surgery was 23.7 days. Results: All flaps survived without complication. All patients regained a good range of motion in the affected extremity. Donor site morbidities were not observed. The case with digital nerve reconstruction recovered a static two point discrimination of 7 mm. The patient with foot reconstruction can wear normal shoes without a debulking procedure. Conclusion: The majority of soft tissue affection after snake bites can be treated conservatively. Some severe cases, however, may require the coverage with flap surgery after radical debridement, especially, if there is exposure of tendon, bone or neurovascular structures. There is no doubt that definite coverage should be performed as soon as possible. But we also want to point out that this principle must not lead to a premature coverage. If the surgeon is not certain that the wound is free of necrotic tissue or remnants of venom, it is better to take enough time to get a proper wound before flap surgery in order to obtain a good functional and cosmetic result.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.117-126
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• 2005

A stoichiometric mixture of evaporating materials for $AgGaS_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $AgGaS_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $590^{\circ}C\;and\;440^{\circ}C$, respectively The temperature dependence of the energy band gap of the $AgGaS_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=2.7284 eV-(8.695{\times}10^{-4}eV/K)T^2/T(T+332K)$. After the as-grown $AgGaS_2$, single crystal thin films was annealed in Ag-, S-, and Ga-atmospheres, the origin of point defects of $AgGaS_2$ single crystal thin films has been investigated by the photoluminescence(PL) at 10K. The native defects of $V_{Ag},\;V_s,\;Ag_{int},\;and\;S_{int}$, obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Ag-atmosphere converted $AgGaS_2$ single crystal thin films to an optical n-type. Also, we confirmed that Ga in $AgGaS_2$ crystal thin films did not form the native defects because Ga in $AgGaS_2$ single crystal thin films existed in the form of stable bonds.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.426-432
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• 1999

A plus-point eddy current test(ECT) probe was developed to examine the defects on the welds of pumps, valves, and pipings which are the major components of the electric power plants, non-destructive evaluation (NDE) techniques for detecting and sizing the flaws were studied adapting this probe. Differential plus-point ECT probe is consists of two "I"-type coils crossed each other and has an advantage having a small influence on the sensitivity by lift-off variation to the conventional types of probe. The specimens with crack-like electro discharge machining(EDM) notches on the weld of type 304 stainless-steel were fabricated in order to evaluate the plus-point ECT probe response to the flaws. NDE techniques to detect and size the flaws and estimate the flaw type were established with this specimens.

• Journal of Navigation and Port Research
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• v.28 no.3
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• pp.233-238
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• 2004

Comer point is a very important information to a pattern recognition of image processing. And so, many researchers develope various detecting comer point algoritms. But, there are some problems to get comer points by 8 directional chain code when the degree of edge line is not integer multiplication of 45 degree. So, we propose a new algorithm which is combined with morphology and human visual conception for optimal comer points without the above defects. We get a good simulation result by this proposed algorithm Ana so, we think this algorithm is very useful to FA(factory automation} and ship's radar system to know some coastal area from its image.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.4
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• pp.393-403
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• 1997

In this paper, we proposed an optimal identification method of identifying the membership func¬tions and the fuzzy rules for the stabilization controller of the nonlinear system by RVEGA( Real Variable Elitist Genetic Algo rithm l. Although fuzzy logic controllers have been successfully applied to industrial plants, most of them have been relied heavily on expert's empirical knowl¬edge. So it is very difficult to determine the linguistic state space partitions and parameters of the membership functions and to extract the control rules. Most of conventional approaches have the drastic defects of trapping to a local minima. However, the proposed RVEGA which is similiar to the processes of natural evolution can optimize simulta¬neously the fuzzy rules and the parameters of membership functions. The validity of the RVEGA - based fuzzy controller was proved through applications to the stabi¬lization problems of an inverted pendulum system with highly nonlinear dynamics. The proposed RVEGA - based fuzzy controller has a swing -. up control mode(swing - up controller) and a stabi¬lization one(stabilization controller), moves a pendulum in an initial stable equilibrium point and a cart in an arbitrary position, to an unstable equilibrium point and a center of the rail. The stabi¬lization controller is composed of a hierarchical fuzzy inference structure; that is, the lower level inference for the virtual equilibrium point and the higher level one for position control of the cart according to the firstly inferred virtual equilibrium point. The experimental apparatus was imple¬mented by a DT -- 2801 board with AID, D/A converters and a PC - 586 microprocessor.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.10
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• pp.427-437
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• 1986

Identification of the plants is not easy task especially in the fields of process control. From this point of view, Kitamori developed a method of control system design based on partial knowledge about controlled processes. However, it is difficult to control the oscillatory plant by kitamori's method. In this paper, we develope a method of partial model matching control system design, which have desirable pole-placements in order to improve the above defects. Design examples are given to illustrate the effectiveness of the method.