• 한국결정성장학회지
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• 제27권6호
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• pp.289-294
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• 2017

원자층 두께의 2차원 나노쉬트(2 dimensional nanosheets)를 이용하여 제작한 필름은 나노쉬트 크기에 따라 다양한 물성을 나타낸다. 이는 필름의 물성이 쉬트와 쉬트 사이 계면물성에 의존하기 때문이다. 따라서 큰 나노쉬트의 합성은 필름의 계면물성 의존도를 줄일 수 있다는 점에서 매우 중요하다. 본 연구에서 단결정 성장된 출발물질과 화학적 박리법을 이용하여 마이크로미터 이상의 크기를 갖는 원자층 두께의 $TiO_x$ 나노쉬트를 제조하는데 성공하였다. 또한 제조 공정 중 유기물을 이용한 박리 단계 시 기계적 원심 교반속도가 나노쉬트 크기와 농도에 밀접히 연관되어 있음을 알 수 있었다.

• 한국결정성장학회지
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• 제30권5호
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• pp.194-199
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• 2020

2차원 층상결정구조를 갖는 금속산화물 나노시트의 조성을 제어함으로써 재료 물성 및 응용의 확장이 가능하다. 본 연구에서 니오비움(Nb)이 도핑 된 타이타늄산화물(TiO_y) 나노시트 합성에 성공함으로써 나노시트의 조성을 순수조성에서 도핑조성으로 확장할 수 있었다. 상세하게는 출발 물질인 층상 구조 금속산화물 합성 시 도핑 조성을 설계(K_0.8Ti_1.73-xNb_xLi_0.27O₄, x = 0, 0.03, 0.07)하고 고상 합성한 후 유기물처리를 통한 화학적 박리를 수행하였다. 이렇게 함으로써 니오비움이 도핑 된 타이타늄산화물 초박막 나노시트를 수득할 수 있었다. 나노시트의 크기는 x-y 방향에서 긴 길이 기준으로 2 ㎛ 이하였으며 두께(z 방향)는 약 1 nm였다. 니오비움의 도핑 여부는 XRD 및 SEM-EDS 분석을 통해 확인할 수 있었다.

• 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.

• 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.

• 한국결정성장학회지
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• 제24권5호
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• pp.207-212
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• 2014

2차원 흑연구조를 갖는 카본나노시트는 큰 비표면적과 우수한 전기적, 화학적 및 기계적 물성으로 인하여 미래소재로 각광받고 있다. 경제적이고 쉬운 카본나노시트의 양산공정개발을 위해 본 연구에서는 메테인($CH_4$)과 프로페인($C_3H_8$) 가스를 이용한 유도 열플라즈마 공정을 통해 기상 합성하여 카본나노시트 분말을 합성하였다. 유도 열플라즈마를 이용한 카본나노시트 합성은 촉매나 증착공정 없이 진행되었으며, 합성된 카본나노시트의 물성을 TEM, Raman, XRD, BET로 분석하였다. 메테인과 프로페인으로부터 합성된 카본 나노시트는 각각 5~6개의 그래핀 층과 15~16개의 그래핀 층으로 이루어진 분말로 합성되었으며 분말의 크기는 약 100 nm임을 확인할 수 있었다.

• Tribology and Lubricants
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• 제35권6호
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• pp.343-349
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• 2019

According to a report in 2011, hexagonal boron nitride demonstrated good solubility in pure water, even without surfactants or organic functionalization. Hexagonal boron nitride nanosheets are an effective lubricant additive, and their solubility in pure water has motivated lubrication engineers to utilize aqueous solutions containing these nanosheets as water-based lubricants. In this study, we measure the width and height of the hexagonal boron nitride nanosheets dispersed in pure water by using the Zetasizer and atomic force microscopy. Without surfactants or functionalization, aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of hexagonal boron nitride nanosheets are synthesized via sonication-assisted hydrolysis. The Zetasizer provides only a one-dimensional size of approximately 410 nm, regardless of the concentration of the solution. Thus, it does not allow the estimation of the shape of the nanosheet. To acquire the three-dimensional size of the nanosheets, atomic force microscopy is employed. The aqueous solutions containing 0.10, 0.07, 0.05, and 0.01 wt% of the hexagonal boron nitride nanosheets show average values of 740, 450, 700, and 610 nm in width, and 37, 26, 33, and 32 nm in thickness, respectively. No significant trend is observed between the concentration of the solution and size of the nanosheets. Therefore, when preparing a water-based lubricant, it may be appropriate to adjust conditions such as ultrasonication time rather than the concentration.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.649-655
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• 2011

Methane direct cracking can be utilized to produce $CO_x$ and $NO_x$-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. We present the results of a systematic study of methane direct cracking using a mixed conducting oxide, Y-doped $BaZrO_3$ ($BaZr_{0.85}Y_{0.15}O_3$), membrane. In this paper, dense $BaZr_{0.85}Y_{0.15}O_3$ membrane with disk shape was successfully sintered at $1400^{\circ}C$ with a relative density of more 93% via addition of 1 wt% ZnO. The ($BaZr_{0.85}Y_{0.15}O_3$) membrane is covered with Pd as catalyst for methane decomposition with an DC magnetron sputtering method. Reaction temperature was $800^{\circ}C$ and high purity methane as reactant was employed to membrane side with 1.5 bar pressure. The $H_2$ produced by the reaction was transported through mixed conducting oxide membrane to the outer side. In addition, it was observed that the carbon, by-product, after methane direct cracking was deposited on the Pd/ZnO-$BaZr_{0.85}Y_{0.15}O_3$ membrane. The produced carbon has a shape of sphere and nanosheet, and a particle size of 80 to 100 nm.