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전민현,Harindra Vedala,김태형,최원봉,최현광,Sookhyun Hwang 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.2
In this study, we fabricated and electrochemically characterized two types of individual carbon nanotube electrodes: an as-produced multi-walled carbon nanotube (MWNT) electrode and a modified MWNT electrode. As-produced MWNTs were electrically contacted with Au/Ti layers using nanolithography and RF magnetron sputtering. Open-ended modified MWNT electrodes were fabricated by reactive ion etching treatment under oxygen atmosphere. We also performed cyclic voltammetry measurements for detecting aqueous dopamine solutions with different concentrations. We found that an individual MWNT electrode, which has a small effective area, shows good electrochemical performance. The electrocatalytic behavior of the modified electrode, which had "broken" open ends were better than that of the as-produced electrode with respect to sensitivity. The modified electrode is capable of detecting dopamine at the picomolar level. Therefore, an individual modified MWNT electrode has potential for application to active components in nanobiosensors.
전민현,황숙현,최현광,김영주,김현국,강명훈,한영문 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.2
We introduce the electrical conductivity (σ) of the substrate as a new variable to control the growth of multi-walled carbon nanotubes (MWNTs) fabricated by using thermal chemical vapor deposition (CVD). P-type silicon (100) substrates with three different electrical conductivities were used to evaluate the growth mode of the MWNTs. We found that a strong correlation existed between the morphology, diameter, length, and density, of the MWNTs and the electrical conductivity of the silicon substrate. As σ of the substrate increased, the catalytic iron-particle density was observed to decrease and the average particle size to increase. Based on our experimental results, we suggest that the electrical conductivity of the substrate could be used as a control parameter for the growth of MWNTs by using thermal CVD without altering other growth parameters.
김도현,전민현,전훈하,임재영,문주호,이성휘,Ved Prakash Verma,최원봉 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III
The optical and the electrical properties of undoped zinc-oxide (ZnO) thin lms of various thicknesseswerecomparedwiththoseofGa-doped(GZO)thinlms. Transparent,high-qualityundoped ZnO and GZO lms were deposited successfully using radio-frequency (RF) sputtering at room temperature. The lms were polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. The lms had an average optical transmission >85 % in the visible partoftheelectromagneticspectrum. TheundopedZnOthinlmsweremoretransparentthanthe GZO thin lms. The ZnO thin-lm transistors (TFTs) were operated in the enhancement mode withathresholdvoltageof2.5V.Incontrary,theGa-dopedZnOTFTswereoperatedinadepletion mode with a threshold voltage of {3.4 V. We successfully demonstrated undoped and the Ga-doped ZnO TFTs by using conventional SiO2 gate insulators at room temperature. We postulate that undoped ZnO lms, which have not been treated to improve the optical properties, can be used, instead of doped ZnO lms, in transparent devices for next generation optoelectronic devices. The optical and the electrical properties of undoped zinc-oxide (ZnO) thin films of various thicknesses were compared with those of Ga-doped (GZO) thin films. Transparent, high-quality undoped ZnO and GZO films were deposited successfully using radio-frequency (RF) sputtering at room temperature. The films were polycrystalline with a hexagonal structure and a strongly preferred orientation along the $c$-axis. The films had an average optical transmission $>$85 \% in the visible part of the electromagnetic spectrum. The undoped ZnO thin films were more transparent than the GZO thin films. The ZnO thin-film transistors (TFTs) were operated in the enhancement mode with a threshold voltage of 2.5 V. In contrary, the Ga-doped ZnO TFTs were operated in a depletion mode with a threshold voltage of --3.4 V. We successfully demonstrated undoped and the Ga-doped ZnO TFTs by using conventional SiO$_2$ gate insulators at room temperature. We postulate that undoped ZnO films, which have not been treated to improve the optical properties, can be used, instead of doped ZnO films, in transparent devices for next generation optoelectronic devices.
양자점 층의 미세구조 형상이 양자점 LED 전계 발광 특성에 미치는 효과
윤성룡,전민현,이전국,Yoon, Sung-Lyong,Jeon, Minhyon,Lee, Jeon-Kook 한국재료학회 2013 한국재료학회지 Vol.23 No.8
Quantum dots(QDs) with their tunable luminescence properties are uniquely suited for use as lumophores in light emitting device. We investigate the microstructural effect on the electroluminescence(EL). Here we report the use of inorganic semiconductors as robust charge transport layers, and demonstrate devices with light emission. We chose mechanically smooth and compositionally amorphous films to prevent electrical shorts. We grew semiconducting oxide films with low free-carrier concentrations to minimize quenching of the QD EL. The hole transport layer(HTL) and electron transport layer(ETL) were chosen to have carrier concentrations and energy-band offsets similar to the QDs so that electron and hole injection into the QD layer was balanced. For the ETL and the HTL, we selected a 40-nm-thick $ZnSnO_x$ with a resistivity of $10{\Omega}{\cdot}cm$, which show bright and uniform emission at a 10 V applied bias. Light emitting uniformity was improved by reducing the rpm of QD spin coating.At a QD concentration of 15.0 mg/mL, we observed bright and uniform electroluminescence at a 12 V applied bias. The significant decrease in QD luminescence can be attributed to the non-uniform QD layers. This suggests that we should control the interface between QD layers and charge transport layers to improve the electroluminescence.
Voltage Controlled Equivalent Circuit of a Nanowire Memristor
김부강,전민현,송한정 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.12
In this paper, we describe a voltage-driven equivalent circuit of a nanowire memristor based on a metal oxide semiconductor field effect transistor (MOSFET) variable resistor for circuit simulation. The proposed model makes various hysteresis I-V (current−voltage) loops of the memristor based on the control voltage. The equivalent circuit is composed of two multipliers, several fixed resistors, three amplifiers, and a variable MOS resistor for slope control of the emulated memristor. The electric characteristics, such as the time waveform and the current−voltage curves, were examined by using the SPICE (simulation program with integrated circuit emphasis). We obtained many hysteresis I-V curves from the circuit model of the equivalent memristor. In addition, the circuit was experimentally implemented by using a hybrid electronic circuit on which measurements were taken. The simulated data and the measured results obtained through the time series waveforms and the current−voltage curve plots verified that the nonlinear dynamics of the nanowire memristor could be created and controlled by using a variable MOS resistor.
Structural and Optical Properties of InAlAs Graded Buffers on GaAs (001) for Unipolar Devices
최현광,조중석,전민현,Minhyon Jeon,정연길 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2
We investigate the structural and the optical properties of InAlAs step graded buffers (SGBs) grown on GaAs (001). Metamorphic InAlAs SGBs layers with various indium contents are grown on semi-insulating GaAs (001) substrates by means of molecular beam epitaxy. We change various growth parameters, such as the step number, the step thickness and the total SGB thickness, to optimize the graded buffer for unipolar device applications. The samples are characterized using atomic force microscopy, X-ray diffraction and photoluminescence (PL). Metamorphic InAlAs SGBs above intermediate contents reveal effectiveness for strain relaxation of the metamorphic InAlAs layers; it should be noted that the transport properties of unipolar devices are rather sensitive to the strain. The strain and the mosaicity variations of the metamorphic InAlAs layers depend on the total SGB thickness and the thickness of each step. The PL emissions of the metamorphic InAlAs layers with intermediate contents can support a mechanism for an alloy-hardening gradient.
Hoonha Jeon,전민현,Do-Hyun Kim,Dongjo Kim,문주호,Kyoungseok Noh,Ved Prakash Verma,Wonbong Choi 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III
In this paper we present bottom-gate-type ZnO-based TFTs with low threshold voltages fabricated with a conventional SiO$_2$ gate insulator by radio-frequency (RF) magnetron sputtering at room temperature. The SiO$_2$ is used as a gate insulator, and it is possible to achieve a low gate leakage current ($<$10 pA) by using this conventional SiO$_2$ oxide without new gate oxide materials. The ZnO film also has good uniformity and transparency. The ZnO TFTs operate in the enhancement mode with a threshold voltage of 2.5 V. A mobility of 0.018 cm$^2$/(V$\cdot$s), an on/off ratio of about 10$^4$, and a gate voltage swing of 1.7 V/decade are obtained. We successfully demonstrate that a ZnO TFT with comparable electrical characteristics can be fabricated by utilizing the conventional SiO$_2$ gate insulator. It is also possible to reduce the power consumption due to their low threshold voltage and low leakage current.