• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.281.2-281.2
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• 2016

Two-dimensional van der Waals (2D vdWs) materials have been extensively studied for future electronics and materials sciences due to their unique properties. Among them, black phosphorous (BP) has shown infinite potential for various device applications because of its high mobility and direct narrow band gap (~0.3 eV). In this work, we demonstrate a few-nm thick BP-based nonvolatile memory devices with an well-known poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] ferroelectric polymer gate insulator. Our BP ferroelectric memory devices show the highest linear mobility value of $1159cm^2/Vs$ with a $10^3$ on/off current ratio in our knowledge. Moreover, we successfully fabricate the ferroelectric complementary metal-oxide-semiconductor (CMOS) memory inverter circuits, combined with an n-type $MoS_2$ nanosheet transistor. Our memory CMOS inverter circuits show clear memory properties with a high output voltage memory efficiency of 95%. We thus conclude that the results of our ferroelectric memory devices exhibit promising perspectives for the future of 2D nanoelectronics and material science. More and advanced details will be discussed in the meeting.

• 센서학회지
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• 제27권1호
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• pp.1-5
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• 2018

Two-dimensional (2D) niobate-based nanosheets have attracted attention as high-k dielectric materials. We synthesized strontiumsubstituted calcium niobate ($Ca_{0.8}Sr_{1.2}Nb_3O_{10}$) nanosheets by a two-step cation exchange process from $KCa_{0.8}Sr_{1.2}Nb_3O_{10}$ ceramic. The $K^+$ ions were exchanged with $H^+$ ions, and then H+ ions were exchanged with tetrabutylammonium ($TBA^+$) cations. The $Ca_{0.8}Sr_{1.2}Nb_3O_{10}$ nanosheets were then exfoliated, decreasing the electrostatic interaction between each niobate layer. Furthermore, $Ca_2Nb_3O_{10}$ nanosheets were synthesized in same process for comparison. Each exfoliated nanosheet shows a single-crystal phase and has a lateral size of over 100 nm. The nanosheets were deposited on a $Pt/Ti/SiO_2/Si$ substrate by the electrophoretic deposition (EPD) method at 40 V, followed by ultraviolet irradiation of the films in order to remove the remaining $TBA^+$ ions. The $Ca_{0.8}Sr_{1.2}Nb_3O_{10}$ thin film exhibited twice the dielectric permittivity (~60) and lower dielectric loss than $Ca_2Nb_3O_{10}$ thin films.

• 한국세라믹학회지
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• 제52권3호
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• pp.173-179
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• 2015

We report the facile synthesis of graphene-$CdLa_2S_4$ composite through a facile solvothermal method at low temperature. The as-prepared products were characterized by X-ray diffraction (XRD) and by Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and BET analysis, revealing the uniform covering of the graphene nanosheet with $CdLa_2S_4$ nanocrystals. The as-prepared samples show a higher efficiency for the photocatalytic degradation of typical MB dye compared with P25 and $CdLa_2S_4$ bulk nanoparticles. The enhancement of visible-light-responsive photocatalytic properties by decolorization of Rh.B dye may be attributed to the following causes. Firstly, graphene nanosheet is capable of accepting, transporting and storing electrons, and thus retarding or hindering the recombination of the electrons with the holes remaining on the excited $CdLa_2S_4$ nanoparticles. Secondly, graphene nanosheet can increase the adsorption of pollutants. The final cause is that their extended light absorption range. This work not only offers a simple way to synthesize graphene-based composites via a one-step process at low temperature but also a path to obtain efficient functional materials for environmental purification and other applications.

• 한국표면공학회지
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• 제54권1호
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• pp.37-42
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• 2021

Electrodeposition is a synthetic method that allows fine control of the nucleation and growth factors of metals and is a suitable method for studying the nucleation and growth of Ni(OH)2. Hexa-methylenetetramine (HMT) helps to form Ni(OH)2 nanosheets by increasing the OH- of the nickel precursor solution and helps to improve the electrochemical properties of the electrode. In this study, the structural properties of Ni(OH)2 nanosheets according to the HMT concentration change using electrodeposition were studied. As the concentration of HMT increased, the size and thickness of the Ni(OH)2 nanosheet adsorbed on the surface increased and porosity increased. Also, the Scharifker-Hills nucleation theory model and experimental data were compared. In conclusion, the nanosheet shape of the HMT 7.5 mM sample electrodeposited with -0.85 V vs. Ag/AgCl grew most uniformly, and the best result was obtained as an electrode material for a pseudocapacitor.

• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.90-99
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• 2022

Owing to the rising concern of global warming, lithium-ion batteries have gained immense attention over the past few years for the development of highly efficient electrochemical energy conversion and storage systems. In this study, alpha-phase VOPO₄·2H₂O with nanosheet morphology was prepared via a facile hydrothermal method for application in high-performance lithium-ion batteries. The X-ray diffraction and scanning electron microscopy (SEM) analyses indicated that the obtained sample had an alpha-2 (αII) phase, and the nanosheet morphology of the sample was confirmed using SEM. The lithium-ion battery with VOPO₄·2H₂O as the anode exhibited excellent long-term cycle life and a high capacity of 256.7 mAh g^-1 at room temperature. Prelithiation effectively improved the specific capacity of pristine VOPO₄·2H₂O. The underlying electrochemical mechanisms were investigated by carrying out AC impedance, rate capability, and other instrumental analyses.

• 한국재료학회지
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• 제32권1호
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• pp.30-35
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• 2022

The development of advanced materials to improve the efficiency of photoelectrochemical (PEC) water splitting paves the way for widespread renewable energy technologies. Efficient photoanodes with strong absorbance in visible light increases the effectiveness of solar energy conversion systems. MoS₂ in a two-dimensional semiconductor that has excellent absorption performance in visible light and high catalytic activity, showing considerable potential as an agent of PEC water splitting. In this study, we successfully modulated the MoS₂ morphology on indium tin oxide substrate by using the metalorganic chemical vapor deposition method, and applied the PEC application. The PEC photocurrent of the vertically grown MoS₂ nanosheet structure significantly increased relative to that of MoS₂ nanoparticles because of the efficient transfer of charge carriers and high-density active sites. The enhanced photocurrent was attributed to the efficient charge separation and improved light absorption of the MoS₂ nanosheet structure. Meanwhile, the photocurrent property of thick nanosheets decreased because of the limit imposed by the diffusion lengths of carriers. This study proposes a valuable photoelectrode design with suitable nanosheet morphology for efficient PEC water splitting.

• 전기전자학회논문지
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• 제27권4호
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• pp.386-390
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• 2023

본 연구에서는 기존 상보성 금속 산화막 반도체 공정을 활용하여 제작된 실리콘 나노시트(SiNS) 피드백 전계효과 트랜지스터(FBFET)의 준비휘발성 메모리 특성을 분석하였다. 과노광공정을 이용하여 형성된 SiNS 채널층의 폭은 180 nm이고 높이는 70 nm이었다. 양성 피드백 루프를 기반으로 동작하는 SiNS FBFET의 낮은 문턱전압이하 기울기는 1.1 mV/dec, ON/OFF 전류비는 2.4×10⁷이었다. 또한 SiNS FBFET는 50 초 동안 상태를 유지하는 메모리 특성을 보여 준휘발성메모리 소자로 활용 가능성을 제시하였다.

• 전기전자학회논문지
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• 제27권4호
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• pp.418-424
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• 2023

본 연구에서는 더블게이트 실리콘 나노시트 (SiNS) 피드백 전계효과 트랜지스터(FBFET)의 전기적 특성에 열처리가 미치는 영향을 분석하였다. 1000 초 동안 바이어스 스트레스를 인가했을 때 더블게이트 SiNS FBFET는 inversion layer의 전자에 의한 계면 트랩의 증가로 인해 채널 모드와 무관하게 negative bias stress 보다는 positive bias stress의 영향을 더 많이 받았다. 300 ℃에서 10 분 동안 열처리를 진행한 이후 소자는 원래의 특성을 완전히 회복하였으며 다시 1000 초 동안 바이어스 스트레스를 인가해도 특성이 변하지 않았다.

• Carbon letters
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• 제14권1호
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• pp.51-54
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• 2013

In this study, polyaniline (PANI)/graphene nanosheet (GNS) composites were synthesized through chemical oxidation polymerization by changing the weight ratio of aniline monomers. To examine the morphological structure of the composites, scanning electron microscopy and transmission electron microscopy (TEM) were conducted. TEM results revealed that fibril-like PANI with a diameter of 50 nm was homogeneously coated on the surface of the GNS. The electrochemical properties of the composites were studied by cyclic voltammetry in 1 M $H_2SO_4$ electrolyte. Among the prepared samples, the PANI/GNS (having 40 wt% aniline content) showed the highest specific capacitance, 528 $Fg^{-1}$, at 10 $mVs^{-1}$. The improved performance was attributed to the GNS, which provides a large number of active sites and good electrical conductivity. The resulting composites are promising electrode materials for high capacitative supercapacitors.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2004년도 춘계학술발표대회 및 제6회 신소재 심포지엄
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• pp.70-70
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• 2004