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Kim, Soo Min,Jang, Jin Ho,Kim, Ki Kang,Park, Hyeon Ki,Bae, Jung Jun,Yu, Woo Jong,Lee, Il Ha,Kim, Gunn,Loc, Duong Dinh,Kim, Un Jeong,Lee, Eun-Hong,Shin, Hyeon-Jin,Choi, Jae-Young,Lee, Young Hee American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.1
<P>Various viologens have been used to control the doping of single-walled carbon nanotubes (SWCNTs) via direct redox reactions. A new method of extracting neutral viologen (V(0)) was introduced using a biphase of toluene and viologen-dissolved water. A reductant of sodium borohydride transferred positively charged viologen (V(2+)) into V(0), where the reduced V(0) was separated into toluene with high separation yield. This separated V(0) solution was dropped on carbon nanotube transistors to investigate the doping effect of CNTs. With a viologen concentration of 3 mM, all the p-type CNT transistors were converted to n-type with improved on/off ratios. This was achieved by donating electrons spontaneously to CNTs from neutral V(0), leaving energetically stable V(2+) on the nanotube surface again. The doped CNTs were stable in water due to the presence of hydrophobic V(0) at the outermost CNT transistors, which may act as a protecting layer to prevent further oxidation from water.</P>
Plasmon-Enhanced Ultraviolet Photoluminescence from Hybrid Structures of Graphene/ZnO Films
Hwang, Sung Won,Shin, Dong Hee,Kim, Chang Oh,Hong, Seung Hui,Kim, Min Choul,Kim, Jungkil,Lim, Keun Yong,Kim, Sung,Choi, Suk-Ho,Ahn, Kwang Jun,Kim, Gunn,Sim, Sung Hyun,Hong, Byung Hee American Physical Society 2010 Physical Review Letters Vol.105 No.12
<P>We report substantially enhanced photoluminescence (PL) from hybrid structures of graphene/ZnO films at a band gap energy of ZnO (??.3??eV/376??nm). Despite the well-known constant optical conductivity of graphene in the visible-frequency regime, its abnormally strong absorption in the violet-frequency region has recently been reported. In this Letter, we demonstrate that the resonant excitation of graphene plasmon is responsible for such absorption and eventually contributes to enhanced photoemission from structures of graphene/ZnO films when the corrugation of the ZnO surface modulates photons emitted from ZnO to fulfill the dispersion relation of graphene plasmon. These arguments are strongly supported by PL enhancements depending on the spacer thickness, measurement temperature, and annealing temperature, and the micro-PL mapping images obtained from separate graphene layers on ZnO films.</P>
van der Waals gap-inserted light-emitting p–n heterojunction of ZnO nanorods/graphene/p-GaN film
Sung Ho Moon,Junseok Jeong,Gwan Woo Kim,Dae Kwon Jin,Yong-Jin Kim,Jong Kyu Kim,Keun Soo Kim,Gunn Kim,Young Joon Hong 한국물리학회 2020 Current Applied Physics Vol.20 No.2
We report on the electroluminescent (EL) and electrical characteristics of graphene-inserted ZnO nanorods (NRs)/p-GaN heterojunction diode. In a comparative study, ZnO NRs/p-GaN and ZnO NRs/graphene/p-GaN heterojunctions exhibit white and yellow EL emissions, respectively, at reverse bias (rb) voltages. The different EL colors are results of different dichromatic EL peak intensity ratios between 2.25 and 2.8 eV light emissions which are originated from ZnO and p-GaN sides, respectively. The 2.25 eV EL is predominant in both the heterojunctions, because of recombination by numerous electrons tunneled from p-GaN to ZnO across the thin barriers of the staggered broken gap with a large band offset in ZnO/p-GaN and the van der Waals (vdW) gap formed by graphene insertion at ZnO NRs/p-GaN. However, as for the 2.8 eV EL intensity, ZnO NRs/graphene/p- GaN hardly shows the EL emission, whereas ZnO NRs/p-GaN exhibits the substantially strong EL peak. We discuss that the significantly reduced 2.8 eV EL emission of ZnO NRs/graphene/p-GaN is a result of decreased depletion layer thickness at p-GaN side where the recombination events occur for 2.8 eV EL before the reverse bias-driven tunneling because the insertion of graphene (or vdW gap barrier) inhibits the carrier diffusion whose amount determines the depletion thickness when forming the heterojunctions. This study opens a way of suppressing (or enhancing) the specific EL wavelength for the dichromatic EL-emitting heterojunctions simply by inserting atom-thick vdW layer.
Gunn Hee Kim,안현주,Hyun-Soo Kim,Si Ra Bang,조현성,양미경,김지애 대한마취통증의학회 2011 Korean Journal of Anesthesiology Vol.60 No.6
Background: Endoscopic thyroidectomy was recently introduced and has been rapidly accepted by surgeons and patients. The present study was conducted to estimate and compare the incidences of postoperative nausea and vomiting (PONV) after endoscopic thyroidectomy using two different anesthetic methods: sevoflurane based balanced anesthesia; total intravenous anesthesia (TIVA). Methods: Ninety nine female patients that were scheduled to undergo elective endoscopic thyroidectomy under general anesthesia were enrolled. These patients were randomly allocated to receive sevoflurane based balanced anesthesia (BA group) or propofol-remifentanil anesthesia (TIVA group). PONV was evaluated using a 4-point Likert scale, and pain using a visual analogue scale (VAS; range 0 to 100) for 0-2, 2-6, and 6-24 hours postoperatively. At 24 hours postoperatively, overall patient satisfaction regarding PONV and pain were recorded. Results: The incidence of PONV was 14.6% in the TIVA group and 51.3% in the BA group. The incidence of nausea at 0-2 and 2-6 hours postoperatively was lower in the TIVA group than in the BA group (4.2% vs. 35.9%, 6.3% vs. 23.1%, respectively), but no between-group difference was observed at 6-24 hours postoperatively (8.3% vs. 5.1%). Antiemetic usage at 0-2 and 2-6 hours was lower in the TIVA than the BA group (4.2% vs. 38.5%, 6.3% vs. 23.1%),but no between-group difference was observed for 6-24 hours (6.3% vs. 7.7%). There were no differences in pain or in patient satisfaction. Conclusions: After endoscopic thyroidectomy, total intravenous anesthesia with propofol-remifentanil is associated with less PONV during the early postoperative period (0-6 hours) than sevoflurane based balanced anesthesia.
Low Temperature Test of HWR Cryomodule
Kim, Heetae,Kim, Youngkwon,Lee, Min Ki,Park, Gunn-Tae,Kim, Wookang The Korean Vacuum Society 2016 Applied Science and Convergence Technology Vol.25 No.3
Low temperature test for half-wave resonator (HWR) cryomodule is performed at the superfluid helium temperature of 2 K. The effective temperature is defined for non-uniform temperature distribution. Helium leak detection techniques are introduced for cryogenic system. Experimental set up is shown to make the low temperature test for the HWR cryomodule. The cooldown procedure of the HWR cryomodule is shown from room temperature to 2 K. The cryomodules is precooled with liquid nitrogen and then liquid helium is supplied to the helium reservoirs and cavities. The pressure of cavity and chamber are monitored as a function of time. The vacuum pressure of the cryomodule is not increased at 2 K, which shows leak-tight in the superfluid helium environment. Static heat load is also measured for the cryomodule at 2.5 K.
High-Speed Real-Time Monitoring of Electronic Control Units
Gunn Kim 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A new method for monitoring Electronic Control Units deterministically at a high speed in real-time has been developed. An operating ECU generates a monitoring data packet at each execution cycle, right after completing the intrinsic control routines, only if commanded by the monitoring equipment. The monitoring data packet is transmitted through the SPI communication port on the MCU at a maximum transfer rate of 20 Mbps. The ECU operates in master mode and the monitoring equipment operates in slave mode for the high-speed synchronous serial data communication. The SPI communication supports a character length of either 8 bits or 16 bits. The monitoring equipment and ECU are connected to each other through a shielded or unshielded twisted 4-pair cable whose quality is better than CAT5, and the balanced differential interface standard RS-422 is employed between them. It is shown that the interface circuit on the ECU can be implemented simply by using three pieces of RS-422 transceiver along with a set of three resistors consisting of an impedance termination resistor and two open-line failsafe termination resistors. A monitoring data block consists of the user-defined monitoring variables, data types of which may include 8/16/32-bit signed/unsigned integer and 32-bit IEEE-754 floating-point numbers. Three examples are presented to show that this monitoring method can be applied to verify and debug the CPU firmware as well as the electronic circuit of a target embedded system in real-time when the target embedded system is analyzed with the breakthrough monitoring equipment, i.e. Digital LogicScope™.
Na-Ion Anode Based on Na(Li,Ti)O<sub>2</sub> System: Effects of Mg Addition
Kim, Soo Hwa,Bae, Dong-Sik,Kim, Chang-Sam,Lee, June Gunn The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.3
This study involves enhancing the performance of the $Na(Li,Ti)O_2$ system as an Na-ion battery anode with the addition of Mg, which partially replaces Li ions. We perform both computational and experimental approaches to achieve a higher reversible capacity and a faster transport of Na ions for the devised system. Computational results indicate that the $Na(Li,Mg,Ti)O_2$ system can provide a lower-barrier path for Na-ion diffusion than can a system without the addition of Mg. Experimentally, we synthesize various $Na_z(Li_y,Mg_x,Ti)O_2$ systems and evaluate their electrochemical characteristics. In agreement with the theoretical study, Mg addition to such systems improves general cell performance. For example, the prepared $Na_{0.646}(Li_{0.207}Mg_{0.013}Ti_{0.78})O_2$ system displays an increase in reversible capacity of 8.5% and in rate performance of 13.5%, compared to those characteristics of a system without the addition of Mg. Computational results indicate that these improvements can be attributed to the slight widening of the Na-$O_6$ layer in the presence of Mg in the $(Li,Ti)O_6$ layer.