• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.10-14
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• 2008

We synthesized GaN nanowires with high quality using the vapor phase epitaxy technique. The GaN nanowires were obtained at a temperature of $950^{\circ}C$. The Ar and $NH_3$ flow rates were 1000 sccm and 50 sccm, respectively. The shape of the GaN nanowires was confirmed through FESEM analysis. We were able to conclude that the GaN nanowires synthesized via vapor-solid (VLS) mechanism when the source was closed to the substrate. On the other side, the VS mechanism changed to vapor-liquid-solid (VLS) as the source and the substrate became more distant. Therefore, we can suggest that the large amount of Ga source from initial growth interrupt the role of catalyst on the substrate.

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.668-672
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• 2003

The ZnO nanorods were synthesized using vapor-solid (VS) method on sodalime glass substrate without the presence of metal catalyst. ZnO nanorods were prepared thermal evaporation of Zn powder at $500^{\circ}C$. As-fabricated ZnO nanorods had an average diameter and length of 85 nm and 1.7 $\mu\textrm{m}$. Transmission electron microscopy revealed that the ZnO nanorods were single crystalline with the growth direction perpendicular to the (101) lattice plane. The influences of reaction time on the formation of the ZnO nanorods were investigated. The photoluminescence measurements showed that the ZnO nanorods had a strong ultraviolet emission at around 380 nm and a green emission at around 500 nm.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.288-288
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• 2013

Lithium-ion battery (LIB) is one of the most important rechargeable battery and portable energy storage for the electric digital devices. In particular, study about the higher energy capacity and longer cycle life is intensively studied because of applications in mobile electronics and electric vehicles. Generally, the LIB's capacity can be improved by replacing anode materials with high capacitance. The graphite, common anode materials, has a good cyclability but shows limitations of capacity (~374 mAh/g). On the contrary, silicon (Si) and germanium(Ge), which is same group elements, are promising candidate for high-performance LIB electrodes because it has a higher theoretical specific capacity. (Si:4200 mAh/g, Ge:1600 mAh/g) However, it is well known that Si volume change by 400% upon full lithiation (lithium insertion into Si), which result in a mechanical pulverization and poor capacity retention during cycling. Therefore, variety of nanostructure group IV elements, including nanoparticles, nanowires, and hollow nanospheres, can be promising solution about the critical issues associated with the large volume change. However, the fundamental research about correlation between the composition and structure for LIB anode is not studied yet. Herein, we successfully synthesized various structure of nanowire such as Si-Ge, Ge-Carbon and Si-graphene core-shell types and analyzed the properties of LIB. Nanowires (NWs) were grown on stainless steel substrates using Au catalyst via VLS (Vapor Liquid Solid) mechanism. And, core-shell NWs were grown by VS (Vapor-Solid) process on the surface of NWs. In order to characterize it, we used FE-SEM, HR-TEM, and Raman spectroscopy. We measured battery property of various nanostructures for checking the capacity and cyclability by cell-tester.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.13-17
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• 2002

Ga$_2$O$_3$ nanomaterials were synthesized from mechanically ground GaN powders with thermal annealing Ga$_2$O$_3$ nanobelts were farmed in a nitrogen atmosphere, while Ga$_2$O$_3$ nanoparticles were formed inan oxygen atmosphere. The structural properties of the Ga$_2$O$_3$ nanomaterials were investigated by X-ray diffractometer (XRD) and high-resolution transmission eleotron microscope (HRTEM). The study of field emission scanning electron microscopy (FESEM) on the microstructures of nanomaterials revealed that the nanobelts are with the range of about 10∼200nm width and 10∼50nm thickness, and that nanoparticles are with the range of about 20∼50nm radius. On the basis of XRD and HRTEM data, we determined that the nanobelts grow toward a direction perpendicular to the (010) lattice plane and that they are enclosed by facets of the (10T) and (101) lattice planes. The formation of the nanobelts may be described by the vapor-solid(VS) mechanism, and the supersaturation device of gaseous phase may play an important role in the formation of Ga$_2$O$_3$ nanomaterials.

• Bulletin of the Korean Chemical Society
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• v.25 no.1
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• pp.51-54
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• 2004

Gallium nitride (GaN) powders were prepared by calcining a gallium(III) nitrate salt in flowing ammonia in the temperature ranging from 500 to 1050 $^{\circ}C$. The process of conversion of the salt to GaN was monitored by X-ray diffraction and $^{71}Ga$ MAS (magic-angle spinning) NMR spectroscopy. The salt decomposed to ${\gamma}-Ga_2O_3$ and then converted to GaN without ${\gamma}-{\beta}Ga_2O_3$ phase transition. It is most likely that the conversion of ${\gamma}-Ga_2O_3$ to GaN does not proceed through $Ga_2O$ but stepwise via amorphous gallium oxynitride ($GaO_xN_y$) as intermediates. The GaN nanowires and microcrystals were obtained by calcining the pellet containing a mixture of ${\gamma}-Ga_2O_3$ and carbon in flowing ammonia at 900 $^{\circ}C$ for 15 h. The growth of the nanowire might be explained by the vapor-solid (VS) mechanism in a confined reactor. Room-temperature photoluminescence spectra of as-synthesized GaN powders obtained showed the emission peak at 363 nm.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.150-150
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• 2016

Mankind is enjoying a great convenience of their life by the rapid growth of secondary industry since the Industrial Revolution and it is possible due to the invention of huge power such as engine. The automobile which plays the important role of industrial development and human movement is powered by the Engine Module, and especially Diesel engine is widely used because of mechanical durability and energy efficiency. The main work mechanism of the Diesel engine is composed of inhalation of the organic material (coal, oil, etc.), combustion, explosion and exhaust Cycle process then the carbon compound emissions during the last exhaust process are essential which is known as the major causes of air pollution issues in recent years. In particular, COx, called carbon oxide compound which is composed of a very small size of the particles from several ten to hundred nano meter and they exist as a suspension in the atmosphere. These Diesel particles can be accumulated at the respiratory organs and cause many serious diseases. In order to compensate for the weak point of such a Diesel Engine, the DPF(Diesel Particulate Filter) post-cleaning equipment has been used and it mainly consists of ceramic materials(SiC, Cordierite etc) because of the necessity for the engine system durability on the exposure of high temperature, high pressure and chemical harsh environmental. Ceramic Material filter, but it remains a lot of problems yet, such as limitations of collecting very small particles below micro size, high cost due to difficulties of manufacturing process and low fuel consumption efficiency due to back pressure increase by the small pore structure. This study is to test the possibility of new structure by direct infiltration of SiC Whisker on Carbon felt as the next generation filter and this new filter is expected to improve the above various problems of the Ceramic DPF currently in use and reduction of the cost simultaneously. In this experiment, non-catalytic VS CVD (Vapor-Solid Chemical Vaporized Deposition) system was adopted to keep high mechanical properties of SiC and MTS (Methyl-Trichloro-Silane) gas used as source and H2 gas used as dilute gas. From this, the suitable whisker growth for high performance filter was observed depending on each deposition conditions change (input gas ratio, temperature, mass flow rate etc.).

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.97-97
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• 2011

산화아연 (ZnO)은 넓은 에너지 밴드갭 (~3.37 eV), 큰 엑시톤 결합 에너지 (~60 meV) 그리고 높은 전자 이동도 (bulk~300 $cm^2Vs^{-1}$, single nanowire~1000 $cm^2Vs^{-1}$)를 갖고 있어, 광전자 소자 및 반도체소자 응용에 매우 널리 사용되고 있다. 특히, 산화아연 나노로드(ZnO nanorod)는 1차원 나노구조로써 더욱 향상된 전자 이동도와 캐리어의 direct path way를 제공하여 차세대 광전자소자 및 태양광 소자의 응용에 대한 연구가 매우 활발하게 이루어지고 있다. 한편, 이러한 산화아연 나노로드를 성장시키기 위하여 VLS (vapor-liquid-solid), 졸-겔 공정(sol-gel process), 수열합성(hydrothermal synthesis), 전기증착(electrodeposition)등 다양한 방법이 보고되었지만, 이러한 산화아연 나노로드의 성장방법은 실제적인 소자응용을 위한 패터닝 형성에 대하여 제약을 받는 문제점이 있다. 이들 중에서 수열합성법과 전극증착법은 ZnO 또는 AZO (Al doped ZnO) seed 층 표면과 성장용액의 화학반응에 의해서 선택적으로 산화아연 나노로드를 성장시킬 수 있다. 이에 본 연구에서는, 광전자소자의 응용을 위한 간단한 패터닝 공정을 위해, 산화인듐주석(ITO) 박막이 증착된 유리기판(glass substrate)위에 수열합성법과 전극증착법을 이용하여 산화아연 나노로드를 선택적으로 성장시켰다. 실험을 위해, ITO glass 위에 RF magnetron 스퍼터를 사용하여 AZO seed 층을 metal shadow mask를 이용하여 패터닝을 형성한 후, 질산아연과 헥사메틸렌테트라아민으로 혼합된 용액에 $85^{\circ}C$ 온도를 유지하여, 패터닝이 형성된 샘플에 전압을 인가하여 성장시켰다. 나노구조 분석을 위해, 전계주사현미경을 이용하여 수열합성법과 전기증착법에 의한 패터닝된 산화아연 나노로드를 비교하여 관찰하였다.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.118-124
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• 2004

The properties of AlN made by carbothermal reaction depend on the starting materials, quantity of liquid, the liquid-vapor phase reaction, the N$_2$ flow rate, and the reaction temperature. AlN whisker was synthesized by the VLS and VS methods. Solid ${\alpha}$-A1$_2$O$_3$(AES-11) was carbothermally reduced with carbon black in a high-purity N$_2$ atmosphere with AlF$_3$ to cause whisker grown and additional aluminum liquid to increase whisker yield. Aluminum nitride was perfectly formed at reaction temperatures of 1600$^{\circ}C$. At reaction temperature higher than 1600$^{\circ}C$ the aluminum nitride was completely formed, while the composition remains unaffected. Needle-shaped whiskers formed best at 1600$^{\circ}C$ while higher temperatures disrupted whisker formation. Adding 0 to 15 wt% aluminum to the synthesis favorably affects the microstructure for formation of needle-shaped AlN whisker. Additions over 15 wt% degraded formation of AlN whisker.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.11-11
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• 2007

1차원 구조체인 반도체 나노선은 앙자제한효과 (quantum confinement effect) 등을 이용하여 고밀도/고효율의 소자 개발이 기대되고 있다. GaN는 상온에서 3.4 eV의 밴드갭 에너지를 갖는 III-V 족 반도체 재료로써 박막의 경우 광전자 소자로 폭넓게 응용되고 있다. 최근 GaN 나노선의 합성에 성공하면서 발광소자, 고효율의 태양전지, HEMT 등으로의 응용을 위한 많은 연구가 활발히 이루어지고 있다. 하지만, 아직까지 GaN 나노선의 전기적 특성을 제어하는 기술은 확립되지 않고 있다. 본 연구에서는 Vapor solid (VS)법을 이용하여 GaN 나노선을 합성하였으며, GaN 분말과 함께 $Mg_2N_3$ 분말을 첨가하여 (Ga,Mg)N 나노선을 성공적으로 합성하였다. 합성시에 GaN와 Mg 소스간의 거리 변화를 통해 Mg 도핑농도를 제어하고자 하였다. 이 같은 방법으로 합 된 (Ga,Mg)N 나노선의 Mg 도핑농도에 따른 결정학적 특성을 알아보고, (Ga,Mg)N 나노선을 이용하여 소자를 제작한 후 그 전기적 특성을 살펴보고자 한다. X-ray diffraction (XRD)과 high-resolution transmission electron microscopy (HRTEM), EDX를 이용하여 합성된 나노선의 결정학적 특성과 Mg의 도핑 농도를 확인하였다. Photo lithography와 e-beam lithography법을 이용하여 (Ga,Mg)N 나노선 field-effect transistor (FET)를 제작하고, channel current-drain voltage ($I_{ds}-V_{ds}$) 와 channel current-gate voltage ($I_{ds}-V_g$) 측정을 통해 (Ga,Mg)N 나노선이 도핑 농도에 따라 n형에서 p형으로 전기적 특성이 변화함을 확인하였다.

• Polymer(Korea)
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• v.30 no.1
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• pp.85-89
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• 2006

The effect of vapor grown carbon fiber (VGCF) contents on electrical and rheological properties of VGCF filled polyphenylene sulfide (PPS) composites prepared through melt mixing using a twin screw exruder was studied. This method was proved to be quite effective to produce good dispersion of VGCF in the matrix even for highly filled PPS. From the dependence of the electrical conductivity on VGCF content, the percolation phenomena began to occur above $10\;wt\%$. While there is only a marginal increase of viscosity for 1 and $5\;wt\%$ VGCF filled PPS, the composites containing $10\;wt\%$. While VGCF showed abrupt increase in viscosity as well as flattening of frequency vs modulus curve, indicating a transition from a liquid-like to a solid-like behavior due to the creation of VGCF network. This result agrees well to the fact that the network formation in the composite can be composite by rheological property dependence on filler content as well as by electrical conductivity measurement.