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Electrochemically metal-doped reduced graphene oxide films:Properties and applications

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Journal of Materials Science & Technology 2020年第5期40卷 72-80页

作者： Myung-Sic Chae Tae Ho Lee kyung rock son Tae Hoon Park Kyo Seon Hwang Tae Geun Kim School of Electrical Engineering Korea UniversityAnam-ro 145Seongbuk-guSeoul 02841South Korea Department of Clinical Pharmacology and Therapeutics College of MedicineKyung Hee UniversitySeoul 02447South Korea

The fine control of doping levels in graphene materials such as reduced graphene oxide(RGO)is important to properly manipulate their ambipolar transport characteristics for various device ***,conventional doping methods involve complex chemical reactions,large-scale doping processes,and poor ***,a simple and controllable electrochemical doping treatment(EDT),performed via the conductive channels created at the RGO surface by the application of an electric field,is introduced to tailor the electrical properties of RGO films.X-ray photoelectron spectroscopy and Raman spectroscopy measurements are performed to detect the presence of Ni atoms in RGO films after the EDT(EDT-RGO).Then,EDT-RGO field-effect transistors(FETs)are fabricated with different doping areas(0 to 100%fractional area)on the RGO active channel to investigate the effect and selective-area doping capability of the *** to p-type doping compensation by the intercalated Ni atoms,the electron mobility of the EDT-RGO FET decreases from 1.40 to 0.12 cm2 V-1s-1 compared with that of the undoped RGO-FET,leading to the conversion from ambipolar to unipolar p-type transfer characteristics.

关键词： Reduced graphene oxide Electrochemical doping treatment Electrical breakdown process Field-effect transistor

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter:A Universal Approach Toward High-Performance Blue TADF Top Emission OLED

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Nano-Micro Letters 2022年第4期14卷 75-89页

作者： Il Gyu Jang Vignesh Murugadoss Tae Hoon Park kyung rock son Ho Jin Lee WanQi Ren Min Ji Yu Tae Geun Kim School of Electrical Engineering Korea UniversityAnam-ro 145Seongbuk-guSeoul 02841Republic of Korea

A novel device structure for thermally activated delayed fluorescence(TADF)top emission organic light-emitting diodes(TEOLEDs)that improves the viewing angle characteristics and reduces the efficiency roll-off is ***,we describe the design and fabrication of a cavity-suppressing electrode(CSE),Ag(12 nm)/WO_(3)(65 nm)/Ag(12 nm)that can be used as a transparent *** the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency(EQE)and improved angular dependency than the device fabricated using the microcavity-based Ag electrode,it suffers from low color purity and severe efficiency *** drawbacks can be reduced by using an optimized multi-quantum well emissive layer(MQW EML).The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE(18.05%),high color purity(full width at half maximum~59 nm),reduced efficiency roll-off(~46%at 1000 cd m^(−2)),and low angular *** improvements can be attributed to the synergistic effect of the CSE and MQW *** optimized transparent CSE improves charge injection and light outcoupling with low angular dependence,and the MQW EML effectively confines charges and excitons,thereby improving the color purity and EQE *** proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

关键词： Cavity suppression Multi-quantum well Viewing angle Efficiency roll-off Top emission OLED

Manipulation of blue TADF top-emission OLEDs by the first-order optical cavity design:toward a highly pure blue emission and balanced charge transport

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Photonics Research 2021年第8期9卷 1502-1512页

作者： WANQI REN kyung rock son TAE HOON PARK VIGNESH MURUGADOSS TAE GEUN KIM School of Electrical Engineering Korea UniversitySeoul 02841Republic of Korea

The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity ***,a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only *** addition,by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers,light extraction is increased by nearly 2 times compared to the device without a capping ***,the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum,higher maximum current efficiency,and external quantum efficiency compared to the device before *** approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.

关键词： OLEDs tuning charge

Enhanced light emission from AlGaN/GaN multiple quantum wells using the localized surface plasmon effect by aluminum nanoring patterns

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Photonics Research 2018年第1期9卷 30-36页

作者： kyung rock son BYEONG RYONG LEE MIN HO JANG HYUN CHUL PARK YONG HOON CHO TAE GEUN KIM School of Electrical Engineering Korea University Anam-ro 145 Seongbuk-gu Seoul 02841 South Korea Department of Physics and KI for the NanoCentury Korea Advanced Institute of Science and Technology Daejeon 305-701 South Korea

We investigate the localized surface plasmon(LSP) effect by Al nanorings on the AlGaN/GaN multiple quantum well(MQW) structure emitting at 365 nm. For this experiment, first, the size of Al nanorings is optimized to maximize the energy transfer(or coupling) between the LSP and MQW using the silica nanospheres. Then, the Al nanorings with an outer diameter of 385 nm, which exhibit a strong absorption peak in the near-ultraviolet region, are applied to the top surface of the AlGaN/GaN MQW. The photoluminescence(PL) intensity of the MQW structure with Al nanorings increased by 227% at 365 nm compared to that without Al *** improvement is mainly attributed to an enhanced radiative recombination rate in the MQWs through the energy-matched LSPs by the temperature-dependent PL and time-resolved PL analyses. The radiative lifetime was about two times shorter than that of the structure without Al nanorings at room temperature. In addition, the measured PL efficiency at room temperature of the structure with Al nanorings was 33%, while that of the structure without Al nanorings was 19%, implying that LSP-QW coupling together with the nanoring array pattern itself played important roles in the enhancement.

关键词：等离子体通讯技术能量转移量子

Is effect of transcranial direct current stimulation on visuomotor coordination dependent on task difficulty?

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Neural Regeneration Research 2015年第3期10卷 463-466页

作者： Yong Hyun Kwon kyung Woo Kang Sung Min son Na kyung Lee Department of Physical Therapy Yeungnam University College Department of Physical Therapy College of Rehabilitation ScienceDaegu University Department of Physical Therapy College of Health Science Cheongju University

Transcranial direct current stimulation （tDCS）, an emerging technique for non-invasive brain stimulation, is increasingly used to induce changes in cortical excitability and modulate motor behavior, especially for upper limbs. The purpose of this study was to investigate the effects of tDCS of the primary motor cortex on visuomotor coordination based on three levels of task difficulty in healthy subjects. Thirty-eight healthy participants underwent real tDCS or sham tDCS. Using a single-blind, sham-controlled crossover design, tDCS was applied to the primary motor cortex. For real tDCS conditions, tDCS intensity was 1 mA while stimulation was applied for 15 minutes. For the sham tDCS, electrodes were placed in the same position, but the stimu- lator was turned off after 5 seconds. Visuomotor tracking task, consisting of three levels （levels 1, 2, 3） of difficulty with higher level indicating greater difficulty, was performed before and after tDCS application. At level 2, real tDCS of the primary motor cortex improved the accurate index compared to the sham tDCS. However, at levels 1 and 3, the accurate index was not significantly increased after real tDCS compared to the sham tDCS. These findings suggest that tasks of mod- erate difficulty may improve visuomotor coordination in healthy subjects when tDCS is applied compared with easier or more difficult tasks.

关键词： neural regeneration transcranial direct current stimulation visuomotor coordination task difficulty primary motor area motor learning neural regeneration

Does hemispheric lateralization influence therapeutic effects of transcranial direct current stimulation?

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Neural Regeneration Research 2016年第1期11卷 126-129页

作者： Yong Hyun Kwon kyung Woo Kang Na kyung Lee Sung Min son Department of Physical Therapy Yeungnam University College Department of Physical Therapy College of Rehabilitation Science Daegu University Department of Physical Therapy College of Health Science Cheongju University

This study investigated the effect of transcranial direct current stimulation（t DCS） polarity depending on lateralized function of task property in normal individuals performing visuomotor and simple repetitive tasks. Thirty healthy participants with no neurological disorders were recruited to participate in this study. Participants were randomly allocated into active or control condition. For the active condition, t DCS intensity was 2 m A with stimulation applied for 15 minutes to the right hemisphere（t DCS condition）. For the sham control, electrodes were placed in the same position, but the stimulator was turned off after 30 seconds（sham condition）. The tapping and tracking task tests were performed before and after for both conditions. Univariate analysis revealed significant difference only in the tracking task. For direct comparison of both tasks within each group, the tracking task had significantly higher Z score than the tapping task in the t DCS group（P 〈 0.05）. Thus, our study indicates that stimulation of the right hemisphere using t DCS can effectively improve visuomotor（tracking） task over simple repetitive（tapping） task.

关键词： nerve regeneration transcranial direct current stimulation visuomotor task tracking task task property hemispheric lateralization neural regeneration

Exercise-induced muscle fatigue in the unaffected knee joint and its influence on postural control and lower limb kinematics in stroke patients

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Neural Regeneration Research 2017年第5期12卷 765-769页

作者： Sun Wook Park Sung Min son Na kyung Lee Department of Physical Therapy Faculty of Health Science Eulji University Department of Physical Therapy College of Health Science Cheongju University Department of Physical Therapy College of Rehabilitation Science Daegu University

This study aimed to investigate the effects of exercise-induced muscle fatigue in the unaffected knee joint on postural control and kinematic changes in stroke patients. Forty participants（20 stroke patients, 20 age-matched healthy participants） were recruited. To induce fatigue, maximum voluntary isometric contractions were performed in the unaffected knee joint in a Leg Extension Rehab exercise machine using the pneumatic resistance. We measured static and dynamic balance and lower-limb kinematics during gait. Changes in postural control parameters anteroposterior sway speed and total center of pressure distance differed significantly between the stroke and control groups. In addition, changes in gait kinematic parameters knee and ankle angles of initial contact differed significantly between stroke（paretic and non-paretic） and control groups. Muscle fatigue in the unaffected knee and ankle impaired postural control and debilitates kinematic movement of ipsilateral and contralateral lower limbs, and may place the fatigued stroke patients at greater risk for falls.

关键词： nerve regeneration knee muscle fatigue stroke postural control gait kinemetics neural regeneration

Detecting cell-secreted growth factors in microfluidic devices using bead-based biosensors

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Microsystems & Nanoengineering 2017年第1期3卷 242-250页

作者： kyung Jin son Pantea Gheibi Gulnaz Stybayeva Ali Rahimian Alexander Revzin Department of Biomedical Engineering University of CaliforniaDavisCalifornia 95616USA Department of Physiology and Biomedical Engineering Mayo ClinicRochesterMinnesota 55905USA

Microfluidic systems provide an interesting alternative to standard macroscale cell cultures due to the decrease in the number of cells and reagents as well as the improved physiology of cells confined to small ***,the tools available for cell-secreted molecules inside microfluidic devices remain *** this paper,we describe an integrated microsystem composed of a microfluidic device and a fluorescent microbead-based assay for the detection of the hepatocyte growth factor(HGF)and the transforming growth factor(TGF)-β1 secreted by primary *** microfluidic system is designed to separate a cell culture chamber from sensing chambers using a permeable hydrogel ***-secreted HGF and TGF-β1 diffuse through the hydrogel barrier into adjacent sensing channels and are detected using fluorescent microbead-based *** specificity of sensing microbeads is defined by the choice of antibodies;therefore,our microfluidic culture system and sensing microbeads may be applied to a variety of cells and cell-secreted factors.

关键词： biosensors growth factors microbead microchamber primary hepatocytes

Effect of Doubling the Ensemble Size on the Performance of Ensemble Prediction in the Warm Season Using MOGREPS Implemented at the KMA

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Advances in Atmospheric Sciences 2013年第5期30卷 1287-1302页

作者： Jun kyung KAY Hyun Mee KIM Young-Youn PARK Joohyung son Department of Atmospheric Sciences Yonsei University Korea Meteorological Administration

Using the Met Office Global and Regional Ensemble Prediction System （MOGREPS） implemented at the Korea Meteorological Administration （KMA）, the effect of doubling the ensemble size on the performance of ensemble prediction in the warm season was evaluated. Because a finite ensemble size causes sampling error in the full forecast probability distribution function （PDF）, ensemble size is closely related to the efficiency of the ensemble prediction system. Prediction capability according to doubling the ensemble size was evaluated by increasing the number of ensembles from 24 to 48 in MOGREPS implemented at the KMA. The initial analysis perturbations generated by the Ensemble Transform Kalman Filter （ETKF） were integrated for 10 days from 22 May to 23 June 2009. Several statistical verification scores were used to measure the accuracy, reliability, and resolution of ensemble probabilistic forecasts for 24 and 48 ensemble member forecasts. Even though the results were not significant, the accuracy of ensemble prediction improved slightly as ensemble size increased, especially for longer forecast times in the Northern Hemisphere. While increasing the number of ensemble members resulted in a slight improvement in resolution as forecast time increased, inconsistent results were obtained for the scores assessing the reliability of ensemble prediction. The overall performance of ensemble prediction in terms of accuracy, resolution, and reliability increased slightly with ensemble size, especially for longer forecast times.

关键词： ensemble prediction ensemble size ensemble transform Kalman filter