• Title/Summary/Keyword: SiO vapor

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Synthesis of High-Quality Monolayer Graphene on Copper foil by Chemical Vapor Deposition

  • Lee, Su-Il;Kim, Yu-Seok;Song, U-Seok;Jo, Ju-Mi;Kim, Seong-Hwan;Park, Jong-Yun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.351-352
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    • 2011
  • 그래핀(Graphene)은 2차원 평면구조의 $sp^2$ 탄소 결합으로 이루어진 물질이다. 일반적으로 그래핀은 탄소 원자 한층 정도의 얇은 두께를 가지면서 강철의 100배 이상 높은 강도, 다이아몬드보다 2배 이상 뛰어난 열 전도성, 그리고 규소보다 100배 이상 빠른 전자이동도 등의 매우 우수한 특성을 지닌다. 그래핀을 합성하거나 얻는 방법에는, 기계적 박리법(Micro mechanical exfoliation), 산화흑연(graphite oxide)을 이용한 reduced graphene oxide(RGO)방법과 탄화 규소(SiC)를 이용한 epitaxial growth 방법 등이 있지만, 대 면적화가 어렵거나 구조적 결함이 큰 문제점이 있다. 반면, 탄화수소(hydrocarbon)를 탄소 공급원으로 하는 열화학 기상 증착법(Thermal chemical vapor deposition, TCVD)은 구조적 결함이 상대적으로 적으면서 대 면적화가 가능하다는 이점 때문에 최근 가장 많이 이용되고 있는 방법이다. TCVD를 이용, 니켈, 몰리브덴, 금, 코발트 등의 금속에서 그래핀 합성연구가 보고되었지만, 대부분 수 층(fewlayer)의 그래핀이 합성되었다. 하지만, 구리 촉매를 이용하는 것이 단층 그래핀 합성에 매우 효율적이라는 연구결과가 보고되었다. 구리의 경우, 낮은 탄소융해도(solubility of carbon) 때문에 표면에서 self limiting 과정을 통하여 단층 그래핀이 합성된다. 그러나 단층 그래핀 일지라도 면저항(sheet resistance)이 매우 높고, 이론적 계산값에 비해 전자이동도(electron mobility)가 낮게 측정된다. 이러한 원인은 구조적 결함에서 기인된 것으로써 산업으로의 응용을 어렵게 만들기 때문에 양질의 단층 그래핀 합성연구는 필수적이다[1,2]. 본 연구에서는 TCVD를 이용하여 구리 포일(25 ${\mu}m$, Alfa Aeser) 위에 메탄가스를 탄소공급원으로 하여 수소를 함께 주입하고, 메탄가스의 양과 합성시간, 열처리 시간을 조절하면서 균일한 단층 그래핀을 합성하였다. 합성된 그래핀을 $SiO_2$ (300 nm)기판위에 전사(transfer)후 라만 분광법(raman spectroscopy)과 광학 현미경(optical microscope)을 통하여 분석하였다. 그 결과, 열처리 시간이 증가할수록 촉매로 사용된 구리 포일의 grain size가 커짐을 확인하였으며, 구리 포일 위에 합성된 그래핀의 grain size는, 구리 포일의 grain size에 의존하여 커짐을 확인하였다. 또한 동일한 grain 내의 그래핀은 균일한 층으로 합성되었다. 이는 기계적 박리법, RGO 방법, epitaxial growth 방법으로 얻은 그래핀과 비교하여 매우 뛰어난 결정성을 지님이 확인되었다. 본 연구를 통하여 면적이 넓으면서도 결정성이 매우 뛰어난 양질의 단층 그래핀 합성 방법을 확립하였다.

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Design and Optimization of Pilot-Scale Bunsen Process in Sulfur-Iodine (SI) Cycle for Hydrogen Production (수소 생산을 위한 Sulfur-Iodine Cycle 분젠반응의 Pilot-Scale 공정 모델 개발 및 공정 최적화)

  • Park, Junkyu;Nam, KiJeon;Heo, SungKu;Lee, Jonggyu;Lee, In-Beum;Yoo, ChangKyoo
    • Korean Chemical Engineering Research
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    • v.58 no.2
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    • pp.235-247
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    • 2020
  • Simulation study and validation on 50 L/hr pilot-scale Bunsen process was carried out in order to investigate thermodynamics parameters, suitable reactor type, separator configuration, and the optimal conditions of reactors and separation. Sulfur-Iodine is thermochemical process using iodine and sulfur compounds for producing hydrogen from decomposition of water as net reaction. Understanding in phase separation and reaction of Bunsen Process is crucial since Bunsen Process acts as an intermediate process among three reactions. Electrolyte Non-Random Two-Liquid model is implemented in simulation as thermodynamic model. The simulation results are validated with the thermodynamic parameters and the 50 L/hr pilot-scale experimental data. The SO2 conversions of PFR and CSTR were compared as varying the temperature and reactor volume in order to investigate suitable type of reactor. Impurities in H2SO4 phase and HIX phase were investigated for 3-phase separator (vapor-liquid-liquid) and two 2-phase separators (vapor-liquid & liquid-liquid) in order to select separation configuration with better performance. The process optimization on reactor and phase separator is carried out to find the operating conditions and feed conditions that can reach the maximum SO2 conversion and the minimum H2SO4 impurities in HIX phase. For reactor optimization, the maximum 98% SO2 conversion was obtained with fixed iodine and water inlet flow rate when the diameter and length of PFR reactor are 0.20 m and 7.6m. Inlet water and iodine flow rate is reduced by 17% and 22% to reach the maximum 10% SO2 conversion with fixed temperature and PFR size (diameter: 3/8", length:3 m). When temperature (121℃) and PFR size (diameter: 0.2, length:7.6 m) are applied to the feed composition optimization, inlet water and iodine flow rate is reduced by 17% and 22% to reach the maximum 10% SO2 conversion.

A Study on the Atomic-Layer Deposition Mechanism and Characteristics of TiN Films Deposited by Cycle-CVD (Cycle-CVD법으로 증착된 TiN 박막의 ALD 증착기구와 특성에 관한 연구)

  • Min, Jae-Sik;Son, Young-Woong;Kang, Won-Gu;Kang, Sang-Won
    • Korean Journal of Materials Research
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    • v.8 no.5
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    • pp.377-382
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    • 1998
  • Atomic layer deposition(ALD) of amorphous TiN films on $SiO_2$ between 17$0^{\circ}C$ and 21O$^{\circ}C$ has been investigated by alternate supply of reactant sources, Ti[N($C_2,H_5,CH_3)_2]_4$ [tetrakis(ethylmethylamminoltitanium: TEMAT] and $NH_3$. Reactant sources were injected into the reactor in the order of TEMAT vapor pulse, Ar gas pulse, $NH_3$. gas pulse and Ar gas pulse. Film thickness per cycle was saturated at around 1.6 monolayer(MU per cycle with sufficient pulse times of reactant sources at 20$0^{\circ}C$. The results suggest that film thickness per cycle could be beyond 1 MLicycie in ALD, which were explained by rechemisorption mechanisms of reactant sources. The ideal linear relationship be¬tween number of cycles and film thickness is confirmed. As a results of surface limited reactions of ALD, step cover¬age was excellent. Particles caused by the gas phase reactions between TEMAT and NH3 were almost free because TEMAT was seperated from $NH_3$ by the Ar pulse. In spite of relatively low substrate temperature, carbon impurity was incorporated below 4 at%.

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입자침전법을 이용한 광도전체 필름의 X선 반응 특성에 관한 연구

  • Choe, Chi-Won;Gang, Sang-Sik;Jo, Seong-Ho;Gwon, Cheol;Nam, Sang-Hui
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2007.06a
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    • pp.176-176
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    • 2007
  • Flat-panel direct conversion detectors used in compound substance of semiconductor are being studied for digital x-ray imaging. Recently, such detectors are deposited by physical vapor deposition(PVD) generally. But, most of materials (HgI2, PbI2, TlBr, PbO) deposited by PVD have shown difficult fabrication and instability for large area x-ray imaging. Consequently, in this paper, we propose applicable potentialities for screen printing method that is coated on a substrate easily. It is compared to electrical properties among semiconductors such as $HgI_2$, $PbI_2$, PbO, HgBrI, InI, and $TlPbI_3$ under investigation for direct conversion detectors. Each film detector consists of an ~25 to $35\;{\mu}m$ thick layer of semiconductor and was coated onto the substrate. Substrates of $2cm{\times}2cm$ have been used to evaluate performance of semiconductor radiation detectors. Dark current, sensitivity and physics properties were measured. Leakage current of $HgI_2$ as low as $9pA/mm^2$ at the operation bias voltage of ${\sim}1V/{\mu}m$ was observed. Such a value is not better than PVD process, but it is easy to be fabricated in high quality for large area x-ray Imaging. Our future efforts will concentrate on optimization of growth of film thickness that is coated onto a-Si TFT array.

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Selective Oxidation of Single Crystalline AlAs layer on GaAs substrate and XPS(X-ray photoelectron spectroscopy) Analysis (GaAs 기판위에 성장된 단결정 AlAs층의 선택적 산화 및 XPS (X-ray photonelectron spectroscopy) 분석)

  • Lee, Suk-Hun;Lee, Young-Soo;Tae, Heung-Sik;Lee, Young-Hyun;Lee, Jung-Hee
    • Journal of Sensor Science and Technology
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    • v.5 no.5
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    • pp.79-84
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    • 1996
  • A $1\;{\mu}m$ thick n-type GaAs layer with Si doping density of $1{\times}10^{17}/cm^{3}$ and a $500{\AA}$ thick undoped single crystalline AlAs layer were subsequently grown by molecular beam epitaxy on the $n^{+}$ GaAs substrate. The AlAs/GaAs layer was oxidized in $N_{2}$ bubbled $H_{2}O$ vapor($95^{\circ}C$) ambient at $400^{\circ}C$ for 2 and 3 hours. From the result of XPS analysis, small amounts of $As_{2}O_{3}$, AlAs, and elemental As were found in the samples oxidized up to 2 hours. After 3 hours oxidation, however, various oxides related to As were dissolved and As atoms were diffused out toward the oxide surface. The as-grown AlAs/GaAs layer was selectively converted to $Al_{2}O_{3}/GaAs$ at the oxidation temperature $400^{\circ}C$ for 3 hours. The oxidation temperature and time is very critical to stop the oxidation at the AlAs/GaAs interface and to form a defect-free surface layer.

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Growth Behavior of Heteroepitaxial β-Ga2O3 Thin Films According to the Sapphire Substrate Position in the Hot Zone of the Mist Chemical Vapor Deposition System (미스트화학기상증착 시스템의 Hot Zone 내 사파이어 기판 위치에 따른 β-Ga2O3 이종 박막 성장 거동 연구)

  • Kyoung-Ho Kim;Heesoo Lee;Yun-Ji Shin;Seong-Min Jeong;Si-Young Bae
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.36 no.5
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    • pp.500-504
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    • 2023
  • In this study, the heteroepitaxial thin film growth of β-Ga2O3 was studied according to the position of the susceptor in mist-CVD. The position of the susceptor and substrate was moved step by step from the center of the hot zone to the inlet of mist in the range of 0~50 mm. It was confirmed that the average thickness increased to 292 nm (D1), 521 nm (D2), and 580 nm (D3) as the position of the susceptor moved away from the center of the hot zone region. The thickness of the lower region of the substrate is increased compared to the upper region. The surface roughness of the lower region of the substrate also increased because the nucleation density increased due to the increase in the lifetime of the mist droplets and the increased mist density. Therefore, thin film growth of β-Ga2O3 in mist-CVD is performed by appropriately adjusting the position of the susceptor (or substrate) in consideration of the mist velocity, evaporation amount, and temperature difference with the substrate, thereby determining the crystallinity of the thin film, the thickness distribution, and the thickness of the thin film. Therefore, these results can provide insights for optimizing the mist-CVD process and producing high-quality β-Ga2O3 thin films for various optical and electronic applications.

Formation of GaN microstructures using metal catalysts on the vertex of GaN pyramids (금속촉매를 이용한 GaN 피라미드 꼭지점 위의 마이크로 GaN 구조 형성)

  • Yun, W.I.;Jo, D.W.;Ok, J.E.;Jeon, H.S.;Lee, G.S.;Jung, S.K.;Bae, S.M.;Ahn, H.S.;Yang, M.
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.21 no.3
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    • pp.110-113
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    • 2011
  • In this paper, we propose a new method for the fabrication of GaN microstructures formed only on the vertex of GaN pyramid by using of metal catalysts. GaN pyramidal structures were selectively grown on 3 ${\mu}m$ $SiO_2$ dot patterns followed by thin film deposition of Au and Cr only on the vertex area of the GaN pyramids with precisely controlled photolithography. After the metal deposition, the samples were loaded in the MOVPE reactor for the growth of GaN microstructures for 10 minutes. Temperature for the growth of the GaN microstructures was changed from $650^{\circ}C$ to $750^{\circ}C$. Rod type GaN microstructures were grown in the direction of vertical to the six {1-101} facets and the shape of the GaN microstructures was changed depend on the type of metal.

Pervaporation of Aqueous iso-Propyl Alcohol Solution using NaA Zeolite Membrane (이소프로필 알코올 수용액의 NaA 제올라이트 분리막을 이용한 투과증발)

  • Lee Yong-Taek;Lee Hye-Ryeon;Ahn Hyo-Seong;Park In-Jun;Lee Soo-Bok
    • Membrane Journal
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    • v.16 no.1
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    • pp.25-30
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    • 2006
  • The NaA zeolite membrane was synthesized on the surface of a porous ${\alpha}$-alumina support from the reaction solution composed of 1Si : 1Na : 4Na $6H_{2}O$. The pervaporation performance of the synthesized NaA zeolite membrane was investigated for the iso-propyl alcohol (IPA) aqueous solution according to the different feed concentration and the different operating temperature. The total flux decreases by increasing the feed IPA concentration and increases by increasing the temperature. The total flux was about $4.0{\times}10^3g/m^2\;hr\;at\;60^{\circ}C$ and 0.6 mole fraction of IPA and the separation factor was $1.8{\times}10^7\;at\;60^{\circ}C$ and 0.8 mole fraction of IPA. The separation performance of water through the NaA membrane was found to be superior to that obtainable with a distillation process just by comparison of the vapor-liquid equilibrium data.

Crystallographic Studies of Dehydrated Zeolite-X Reacting with Rubidium Vapor (루비듐 증기로 처리한 탈수한 제올라이트 X의 결정학적 연구)

  • Han, Young Wook
    • Journal of the Mineralogical Society of Korea
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    • v.6 no.2
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    • pp.116-121
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    • 1993
  • A single crystla of zeolite $Na_{78}Rb_{28}-X$ (approximate composition) was prepared by exposing $Na_{92}-X$ at $350^{\circ}C$ to 0.1 Torr of rubidium vapor, and its structure was determined by single-crystal x-ray diffraction methods in the cubic space group, Fd3, ${\alpha}=25.045(4){\AA}$. The structure was refined to the final error indices $R_1=0.082$ and $R_2=0.084$ with 353 for which I>$3{\sigma}(I)$. Only about 28 of the 92 $Na^+$ ions per unit cell were reduced and only about 14 of the 28 $Na^0$ atoms produced were retained within the zeolite. A $Na_5{^{4+}}$ cluster is present within each sodalite cavity. It is a centered tetrahedron (like $CH_4$) with bond $length=2.80(2){\AA}$ and angle tetrahedral by symmetry, and shows the full symmetry of its site. $T_d$, at the center of the sodalite cavity. Each of the four terminal atoms of the $Na_5{^{4+}}$ cluster bond to three framework oxygens at $2.36(2){\AA}$. At the centers of some double 6-rings are sodium atoms which bridge linearly between $Na_5{^{4+}}$ clusters to form agglomerations such as short zig-zag chains $Na_5{^{4+}}$ clusters. Delocalized electrons, located primarily on the sodiums at centers of the sodalite and (likely) double-six-ring cavities, contribute to the stability of the clusters.

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A High-Resolution Transmission Electron Microscopy Study of the Grain Growth of the Crystalline Silicon in Amorphous Silicon Thin Films (비정질 실리콘 박막에서 결정상 실리콘의 입자성장에 관한 고분해능 투과전자현미경에 의한 연구)

  • 김진혁;이정용;남기수
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.7
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    • pp.85-94
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    • 1994
  • A high-resolution transmission electron microscopy study of the solid phase crystallization of the amorphous silicon thin films, deposited on SiOS12T at 52$0^{\circ}C$ by low pressure chemical vapor deposition and annealed at 55$0^{\circ}C$ in a dry N$_{2}$ ambient was carried out so that the arrangement of atoms in the crystalline silicon and at the amorphous/crystalline interface of the growing grains could be understood on an atomic level. Results show that circular crystalline silicon nuclei have formed and then the grains grow to an elliptical or dendritic shape. In the interior of all the grains many twins whose{111} coherent boundaries are parallel to the long axes of the grains are observed. From this result, it is concluded that the twins enhance the preferential grain growth in the <112> direction along {111} twin planes. In addition to the twins. many defect such as intrinsic stacking faults, extrinsic stacking faults, and Shockley partial dislocations, which can be formed by the errors in the stacking sequence or by the dissociation of the perfect dislocation are found in the silicon grain. But neither frank partial dislocations which can be formed by the condensation of excess silicon atoms or vacancies and can form stacking fault nor perfect dislocations which can be formed by the plastic deformation are observed. So it is concluded that most defects in the silicon grain are formed by the errors in the stacking sequence during the crystallization process of the amorphous silicon thin films.

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