• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 추계학술대회 초록집
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• pp.186-187
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• 2009

단일 나노선 적용 센서의 단점을 극복하고 신뢰성이 높은 센서를 구현하고자 vapor-liquid-solid (VLS) 법을 이용하여 $SnO_2$ 나노선의 선택적 성장을 통한 나노선 네트워크 구조의 센서를 제조하였다. 분리된 전극층의 변화에 따른 나노선의 접합 특성 변화에 이에 따른 나노선 네트워크 센서의 가스감지 특성을 고찰하였다.

• Transactions on Electrical and Electronic Materials
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• 제14권3호
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• pp.148-151
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• 2013

The control of Ga doping in ZnO nanowires (NWs) by physical vapor deposition has been implemented and characterized. Various Ga-doped ZnO NWs were grown using the vapor-liquid-solid (VLS) method, with Au catalyst on c-plane sapphire substrate by hot-walled pulsed laser deposition (HW-PLD), one of the physical vapor deposition methods. The structural, optical and electrical properties of Ga-doped ZnO NWs have been systematically analyzed, by changing Ga concentration in ZnO NWs. We observed stacking faults and different crystalline directions caused by increasing Ga concentration in ZnO NWs, using SEM and HR-TEM. A $D^0X$ peak in the PL spectra of Ga doped ZnO NWs that is sharper than that of pure ZnO NWs has been clearly observed, which indicated the substitution of Ga for Zn. The electrical properties of controlled Ga-doped ZnO NWs have been measured, and show that the conductance of ZnO NWs increased up to 3 wt% Ga doping. However, the conductance of 5 wt% Ga doped ZnO NWs decreased, because the mean free path was decreased, according to the increase of carrier concentration. This control of the structural, optical and electrical properties of ZnO NWs by doping, could provide the possibility of the fabrication of various nanowire based electronic devices, such as nano-FETs, nano-inverters, nano-logic circuits and customized nano-sensors.

• 한국결정성장학회지
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• 제18권1호
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• pp.10-14
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• 2008

GaN nanowires는 수평 VPE법으로 합성 되었다. 본 실험에서는 source와 기판과의 거리가 합성된 GaN nanowires의 형상에 미치는 영향에 대하여 실험하였다. GaN nanowires는 $950^{\circ}C$ 온도에서 Ar 과 $NH_3$ 가스가 각각 1000, 50 sccm 의 유량에서 합성되었다. 합성된 GaN nanowires의 단면형태는 삼각형의 모양을 가졌으며, GaN nanowires의 길이는 200에서 500 nm 정도 였다. 합성된 GaN nanowires의 모양은 FESEM 으로 확인하였고, XRD 분석을 통하여 그 구조가 wurzite 구조인 것을 확인하였다. 또한, HRTEM 사진과 SAED 패턴을 통하여 합성된 GaN nanowires의 표면과 구조를 분석하였다. 성장된 GaN nanowires의 광학적 특성은 PL분석을 통하여 이루어졌다.

• 한국세라믹학회지
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• 제36권1호
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• pp.36-42
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• 1999

2단계 열탄소환원법으로 탄화규소 휘스커를 기상-고상, 2단계, 기상-액상-고상 성장기구로 각각 합성하였다. 그리고 휘스커에 있는 적층결합을 X-ray와 투과전자현미경을 이용하여 분석하였다. 탄화규소 휘스커에 있는 적층결함은 휘스커의 지름과 상관관계가 있는 것으로 나타났다. 즉, 기상-고상, 2단계 성장, 기상-액상-고상 성장기구에 상관없이 지름이 1$\mu\textrm{m}$이하로 작아지는 경우 적층결합이 많아지고, 기상-액상-고상 기구로 성장한 지름이 2$\mu\textrm{m}$보다 큰 경우 적층결함이 거의 없는 것으로 나타났다. 이같은 현상은 휘스커 지름이 작아짐에 따라 휘스커의 비표면적이 증가하는 때문인 것으로 판단되었다.

• Interaction and multiscale mechanics
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• 제5권4호
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• pp.399-405
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• 2012

A dissipative particle dynamics (DPD) simulation was presented to analyze surface wettability and contact angles of a droplet on a solid platform. The many-body DPD, capable of modeling vapor-liquid coexistence, was used to resolve the vapor-liquid interface of a droplet. We found a constant density inside a droplet with a transition along the droplet boundary where the density decreased rapidly. The contact angle of a droplet was extracted from the isosurfaces of the density generated by the marching cube and a spline interpolation of 2D cutting planes of the isosurfaces. A wide range of contact angles from $55^{\circ}$ to $165^{\circ}$ predicted by the normalized parameter ($|A_{SL}|/B_{SL}$) were reported. Droplet with the parameters $|A_{SL}|>5.84B{_{SL}}^{0.297}$ was found to be hydrophilic. If $|A_{SL}|$ was much smaller than $5.84B{_{SL}}^{0.297}$, the droplet was found to be superhydrophobic.

• Journal of Welding and Joining
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• 제35권2호
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• pp.13-22
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• 2017

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

• 한국분무공학회지
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• 제26권1호
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• pp.1-8
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• 2021

Droplet evaporation has been known as a common phenomenon in daily life, and it has been widely used for many applications. In particular, the influence of the different heated substrates on evaporation flux and flow characteristics is essential in understanding heat and mass transfer of evaporating droplets. This study aims to simulate the droplet evaporation process by considering variation of thermal property depending on the substrates and the surface temperature. The commercial program of ANSYS Fluent (V.17.2) is used for simulating the conjugated heat transfer in the solid-liquid-vapor domains. Moreover, we adopt the diffusion-limited model to predict the evaporation flux on the different heated substrates. It is found that the evaporation rate significantly changes with the increase in substrate temperature. The evaporation rate substantially varies with different substrates because of variation of thermal property. Also, the droplet evaporates more rapidly as the surface temperature increases owing to an increase in saturation vapor pressure as well as the free convection effect caused by the density gradient.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.150-150
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• 2003

wide bind gap과 wurtzite hexagonal structure를 가지고 있으며 청색 발광 및 청자색 레이저 특성을 보이는 III-V족 화합물반도체 GaN는 laser diodes (LD) 및 light emitting diodes (LED) 재료로 주목받고있는 주요 전자재료이다. 본 연구에서는 GaN를 chemical vapor deposition (CVD) 법을 이용하여 vapor-liquid-solid (VLS) mechanisum에 의하여 GaN나노와이어 형태로 성장시켰다. 기판은 (001)Si을 사용하였고 suputtering을 이용하여 GaN와 AlN의 double buffer layer (DBL)를 증착시켰으며 촉매로는 Ni을 사용하였다. 또한, 원료로는 고순도 Ga금속과 NH$_3$ gas를, carrier gas로는 Ar을 사용하여 GaN/AlN/(001)Si 위에 GaN 나노와이어를 성장시켰다. 성장된 GaN 나노와이어는 DBL의 두께, Ga source의 양, 튜브 안의 압력, 튜브 안의 위치 등의 제 공정변수에 따라 tangled, straight 등의 다양한 형상을 보였으며 지름은 약 30~100 nm, 길이는 수 $\mu\textrm{m}$로 관찰되었다. GaN나노와이어의 결정성, 형상 및 발광특성 등을 x-ray diffraction (XRD), photoluminesence (PL), scanning electron microscope (SEM), transmision electron microscope (TEM) 등을 이용하여 측정하였으며 제 공정변수와의 상관관계를 규명하였다.

• 한국세라믹학회지
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• 제44권4호
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• pp.202-207
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• 2007

High-Quality 1-Dimensional InN single crystalline have been grown by Halide Vapor-Phase Epitaxy on the Au catalyst coated Si substrate using the vapor-liquid-solid growth mechanism. We have been grown 1-dimension InN nanowires having controlled the growth conditions for substrate temperature and gases flow rate. The grown InN nanowire of characteristics for morphologies, crystal structure, and element analysis were carried out by SEM, HR-TEM, and EDS respectively. And the defects of InN crystalline were analyzed by indexing of selective area diffraction pattern with attached HR-TEM. We have successfully obtained the defect-free 1-dimensional InN single crystalline nanowire at the atmosphere pressure.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1563-1566
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• 2009

One-dimensional aluminum nitride (AlN) nanostructures were synthesized by calcining an Al(OH)(succinate) complex, which contained a very small amount of iron as a catalyst, under a mixed gas flow of nitrogen and CO (1 vol%). The complex decomposed into a homogeneous mixture of alumina and carbon at the molecular level, resulting in the lowering of the formation temperature of the AlN nanostructures. The morphology of the nanostructures such as nanocone, nanoneedle, nanowire, and nanobamboo was controlled by varying the reaction conditions, including the reaction atmosphere, reaction temperature, duration time, and ramping rate. Iron droplets were observed on the tips of the AlN nanostructures, strongly supporting that the nanostructures grow through the vapor-liquid-solid mechanism. The variation in the morphology of the nanostructures was well explained in terms of the relationship between the diffusion rate of AlN vapor into the iron droplets and the growth rate of the nanostructures.