• 한국산학기술학회논문지
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• 제19권1호
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• pp.699-704
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• 2018

일차원 나노구조물은 양자 갇힘 효과 및 나노와이어가 갖는 체적 대비 높은 표면적 비에 기인하는 독특한 전기적, 광학적, 광전기적, 전기화학적 특성으로 인하여 많은 주목을 받아왔다. 특히 수직으로 성장된 나노와이어는 체적 대비 높은 표면적 비의 특성을 나타낸다. VLS(Vapor-Liquid-Soild) 공정은 나노구조물의 성장 과정에서 자기정렬 효과 때문에 더욱 주목을 받는다. 본 연구에서는 두 영역 열화학 기상증착법을 이용하여 Si\$SiO_2$(300 nm)\Pt 기판 위에 수직으로 정렬된 실리콘 옥사이드 나노기둥을 VLS 공정으로 성장시켰다. 성장된 실리콘 옥사이드 나노기둥의 형상과 결정학적 특성을 주사전자현미경 및 투과전자현미경으로 분석하였다. 그 결과 성장된 실리콘 옥사이드 나노기둥의 지름과 길이는 촉매 박막의 두께에 따라 변하였다. 실리콘 옥사이드 나노 기둥의 몸체는 비정질 상을 나타내었으며, Si과 O로 구성되어 있었다. 또한 성장된 실리콘 옥사이드 나노 기둥의 머리는 결정성을 나타내었으며, Si, O, Pt 및 Ti으로 구성되어 있었다. 실리콘 옥사이드 나노 기둥의 수직 정렬은 촉매물질인 Pt/Ti 합금의 결정성 정렬 선호에 기인하는 것으로 판단되며, 수직 성장된 실리콘 옥사이드 나노기둥은 기능성 나노소재로 활용이 가능할 것으로 기대된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.430.1-430.1
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• 2014

According to advanced nanotechnology in the field of biomedical engineering, many studies of the interaction between topography of surfaces and cellular responses have been focused on nanostructure. In order to investigate this interaction, it is essential to make well-controlled nanostructures. Electron beam lithography (EBL) have been considered the most typical processes to fabricate and control nano-scale patterns. In this work, $TiO_2$ nanowire array was fabricated with hybrid process (top-down and bottom-up processes). Nanodot arrays were patterned on the substrate by EBL process (top-down). In order to control the spacing between nanodots, we optimized the EBL process using Poly(methyl methacrylate) (PMMA) as an electron beam resist. Metal lift-off was used to transfer the spacing-controlled nanodots as a seed pattern of $TiO_2$ nanowire array. Au or Sn nanodots which play an important role for catalyst using Vapor-Liquid-Solid (VLS) method were patterned on the substrate through the lift-off process. Then, the sample was placed in the tube furnace and heated at the synthesis temperature. After heat treatment, $TiO_2$ nanowire array was fabricated from the nanodots through VLS method (bottom-up). These results of spacing-controlled nanowire arrays will be used to study the interaction between nanostructures and cellular responses in our next steps.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.221.1-221.1
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• 2015

The vapor-liquid-solid (VLS) method, where the "liquid" catalytic droplets collecting atoms from vapor precursors build the solid crystal layers via supersaturation, is a ubiquitous technique to synthesize 1-dimensional nanoscale materials. However, the lack of fundamental understanding of chemical information governing the process inhibits the rational route to the structural programming. By combining the in situ or operando IR spectroscopy with post-growth high resolution electron microscopy, we show the strong correlation between the surface chemical species concentration and nanowire structures. More specifically, the critical role of surface adsorbed hydrogen, generated from the decomposition of Si2H6 precursor on the interplay between nanowire / kinking and the defect propagation is demonstrated. Our results show that adsorbed hydrogen atoms are responsible for selecting -oriented growth and indicate that a twin boundary imparts structural coherence. The twin boundary, only continuous at / kinks, reduces the symmetry of the trijunction and limits the number of degenerate directions available to the nanowire. These findings constitute a general approach for rationally engineering kinking superstructures and also provide important insight into the role of surface chemical bonding during VLS synthesis.

• 영어어문교육
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• 제15권4호
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• pp.37-54
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• 2009

This study investigated vocabulary learning strategies used by EFL middle school learners in Korea and examined the relationship between the middle school learners' vocabulary learning strategy (VLS) use and their vocabulary proficiency level. One hundred and forty-one students in a public middle school participated in the study and the data for this study were collected from a vocabulary learning strategy questionnaire and a vocabulary proficiency test. Based on the result of the vocabulary proficiency test, the participants were divided into three proficiency groups: high-, mid- and low- level proficiency groups. The overall findings of the study revealed that the participants used cognitive strategies most frequently and social strategies least frequently. The most frequently used individual strategies were 'using a bilingual dictionary,' 'studying the sound of a word' and 'practicing words through verbal repetition.' The least frequently used ones were 'interacting with native speakers' and 'studying or practicing the meaning of a word in a group.' The research results also showed that the vocabulary proficiency level has a significant influence on the vocabulary strategy use. The more proficient learners used vocabulary learning strategies more actively. More specifically, the high proficiency level group used metacognitive strategies the most. The middle and low proficiency groups used cognitive strategies the most. It is suggested that language teachers should facilitate the vocabulary learning process by helping learners develop appropriate strategies.

• 융합정보논문지
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• 제7권5호
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• pp.123-128
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• 2017

나노구조를 갖는 물질들은 나노구조물이 갖는 고유의 체적 대비 높은 표면적 비와 양자 갇힘 효과에 기인하는 독특한 전기적, 광학적, 광전기적, 자기적 특성으로 인하여 많은 주목을 받아왔다. 열화학 기상 증착 공정은 나노 구조물의 성장과정에서 다양한 구조를 갖는 나노소재의 합성 능력 때문에 더욱 주목을 받아왔다. 본 연구에서는 두 영역 열화학 기상 증착법과 소스 물질 $TiO_2$ 파우더를 이용하여 VLS 공정으로 Si\$SiO_2$(300 nm)\Pt(5~40 nm) 기판 위에 실리콘 옥사이드 나노와이어를 성장시켰다. 성장된 실리콘 옥사이드 나노와이어의 형상과 결정학적 특성을 전계방출 주사전자현미경과 투과전자현미경으로 분석하였다. 분석결과, 성장된 실리콘 옥사이드 나노와이어의 형상인 지름과 길이는 촉매 박막의 두께에 의존하여 다른 모양을 나타내었다. 또한 성장된 실리콘 옥사이드 나노와이어는 비정질 상을 갖는 것으로 분석되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.86-86
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• 2012

The new approaches for silicon solar cell of new concept have been actively conducted. Especially, solar cells with wire array structured radial p-n junctions has attracted considerable attention due to the unique advantages of orthogonalizing the direction of light absorption and charge separation while allowing for improved light scattering and trapping. One-dimenstional semiconductor nano/micro structures should be fabricated for radial p-n junction solar cell. Most of silicon wire and/or pillar arrays have been fabricated by vapour-liquid-solid (VLS) growth because of its simple and cheap process. In the case of the VLS method has some weak points, that is, the incorporation of heavy metal catalysts into the growing silicon wire, the high temperature procedure. We have tried new approaches; one is electrochemical etching, the other is noble metal catalytic etching method to overcome those problems. In this talk, the silicon pillar formation will be characterized by investigating the parameters of the electrochemical etching process such as HF concentration ratio of electrolyte, current density, back contact material, temperature of the solution, and large pre-pattern size and pitch. In the noble metal catalytic etching processes, the effect of solution composition and thickness of metal catalyst on the etching rate and morphologies of silicon was investigated. Finally, radial p-n junction wire arrays were fabricated by spin on doping (phosphor), starting from chemical etched p-Si wire arrays. In/Ga eutectic metal was used for contact metal. The energy conversion efficiency of radial p-n junction solar cell is discussed.

• 한국진공학회지
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• 제22권6호
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• pp.291-297
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• 2013

Au 촉매를 코팅한 사파이어 기판 상에서 산화아연과 흑연 분말을 혼합한 분말재료를 이용하여 VLS (vapor-liquid-solid) 법으로 산화아연 반도체 나노선을 합성하였다. 제조된 산화아연 나노선은 380 nm에서 근 자외선 영역의 NBE (near-band edge) 발광과 600 nm 부근의 가시광선 영역에서 넓게 퍼져 발광하는 상대적으로 강한 DL (deep level) 발광이 확인되었다($I_{NBE}/I_{DL}$ <1). 산화아연 나노선을 효율적인 단일 파장 자외선 발광체에 적용될 수 있도록 NBE 발광을 극대화함과 동시에 DL 발광을 억제시키기 위하여 본 실험에서는 합성된 산화아연 나노선에 수소 플라즈마 처리를 하였다. 플라즈마 처리시간이 길어짐에 따라(120초 이상) 발광특성의 향상정도는 점차로 감소하였지만, 수소 플라즈마 처리를 통해 나노선 내부에 존재하는 불순물 제어 등으로 다소 짧은 시간의 플라즈마 처리로(90초 이내) DL발광대비 NBE발광의 세기가 약 4배로 향상됨을 확인 하였다($I_{NBE}/I_{DL}$ ~4).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.232-232
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• 2010

Recently light emitting diodes (LEDs) have been expected as the new generation light sources because of their advantages such as small size, long lifetime and energy-saving. GaN, as a wide band gap material, is widely used as a material of LEDs and GaN nanorods are the one of the most widely investigated nanostructure which has advantages for the light extraction of LEDs and increasing the active area by making the cylindrical core-shell structure. Lately GaN nanorods are fabricated by various techniques, such as selective area growth, vapor-liquid-solid (VLS) technique. But these techniques have some disadvantages. Selective area growth technique is too complicated and expensive to grow the rods. And in the case of VLS technique, GaN nanorods are not vertically aligned well and the metal catalyst may act as the impurity. So we just tried to grow the GaN nanorods on Si substrate without catalyst to get the vertically well aligned nanorods without impurity. First we deposited the AlN buffer layer on Si substrate which shows more vertical growth mode than sapphire substrate. After the buffer growth, we flew trimethylgallium (TMGa) as the III group source and ammonia as the V group source. And during the GaN growth, we kept the ammonia flow stable and periodically changed the flow rate of TMGa to change the growth mode of the nanorods. Finally, as the optimization, we changed the various growth conditions such as the growth temperature, the working pressure, V/III ratio and the doping level. And we are still in the process to reduce the diameter of the nanorods and to extend the length of the nanorods simultaneously. In this study, we focused on the shape changing of GaN nanorods with different growth conditions. So we confirmed the shape of the nanorods by scanning electron microscope (SEM) and carried out the Photoluminescence (PL) measurement and x-ray diffraction (XRD) to examine the crystal quality difference between samples. Detailed results will be discussed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.243-243
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• 2009

Bi2O3 doped ZnO nanostructures structure were successfully synthesized by a thermal evaporatiion process and their structural characteristics were investigated. It is demonstrated that the growth condition such as the areal density, pretreatment of the substrates and growth temperature have great influence on the morphology and the alignment of the nanorods arrays. The density of Bi2O3 doped ZnO nanostructures is controlled by the gold (Au) nanoparticle density deposited on the silicon substrates. Relatively homogenous size and shape were observed by introducing gold(Au) seed-layer as nucleation centers on the substrates prior to the VLS reaction. The samples were characterized by X-ray diffraction, scanning electron microscopy.

• 한국분말재료학회지
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• 제13권5호
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• pp.305-312
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• 2006

Amorphous carbon nanotubes were synthesized by a reaction of benzene, ferrocene and Na mixture in a small autoclave at temperatures as low as $400^{\circ}C$. The resulting carbon nanotubes were short and straight, but their inner hole was filled with residual products. The addition of quartz to the reacting mixture considerably promoted the formation of carbon nanotubes. A careful examination of powder structure suggested that the nanotubes in this process were mainly formed by surface diffusion of carbon atoms at the surface of solid catalytic particles, not by VLS(vapor-liquid-solid) mechanism.