• 대한화학회지
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• 제61권1호
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• pp.12-15
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• 2017

We presented a mapping the work function of the vanadium pentoxide ($V_2O_5$) nanonet structures by scanning Kelvin probe microscopy (SKPM). In this measurement, the $V_2O_5$ nanonet was self-assembled via dropping the solution of $V_2O_5$ nanowires (NWs) onto the $SiO_2$ substrate and drying the solvent, resulting in the networks of $V_2O_5$ NWs. We found that the SKPM signal as a surface potential of $V_2O_5$ nanonet is attributed to the contact potential difference (CPD) between the work functions of the metal tip and the $V_2O_5$ nanonet. We generated the histograms of the CPD signals obtained from the SKPM mapping of the $V_2O_5$ nanonet as well as the highly ordered pyrolytic graphite (HOPG) which is used as a reference for the calibration of the SKPM tip. By using the histogram peaks of the CPD signals, we successfully estimated the work function of ~5.1 eV for the $V_2O_5$ nanonet structures. This work provides a possibility of a nanometer-scale imaging of the work function of the various nanostructures and helps to understand the electrical characteristics of the future electronic devices.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기물성,응용부문
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• pp.79-81
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• 2002

ZnO 나노와이어는 ZnO 파우더를 볼밀 처리하여 열증착 방법으로 $1380^{\circ}C$에서 촉매없이 Si 기판위에서 합성되었다. 합성된 ZnO 나노와이어의 길이와 직경은 $20{\sim}30{\mu}m$와 $50{\sim}200$ nm 였다. ZnO 나노와이어 표면을 atomic layer deposition(ALD) 방법으로 $Al_2O_3$ 박막을 얇게 코팅하였다. 성장온도는 $300^{\circ}C$였고, 사용한 전구체는 Trimethlaluminum(TMA)와 distilled water($H_2O$) 이다. Transmission electron microscopy(TEM) 으로 측정한 $Al_2O_3$ 박막의 두께는 40 nm 로서 매우 균일하게 ZnO 나노와이어에 증착되었음을 알 수 있었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.106-106
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• 2017

가스센서는 사내 및 산업 환경에서의 유독성 또는 폭발성 가스 검출, 환경 모니터링, 질병 진단 등 매우 다양한 응용분야에서 큰 관심을 가지고 있다. 반도체 금속산화물(SMOs) 기반의 센서 분야에서는 이들의 감도 및 선택성을 향상시키기 위해 많은 노력을 기울이고 있다. 이는 센서의 선택성을 부여하게 되면 다양한 가스들이 존재하는 환경에서도 검출자가 원하는 가스만의 응답을 얻을 수 있기 때문이다. 본 연구에서는 MOF(Metal-Organic Framwork) 기반 멤브레인으로 ZIF-8(Zeolitic Imidazolate Frameworks 구조들 중 하나) 멤브레인 쉘 층을 이용하여 ZnO 나노선에 형성하였다. ZnO 나노선은 VLS공정 (Vapor-Liquid-Solid)을 이용하여 패턴된 전극을 갖는 $SiO_2$-grown Si 웨이퍼 상에 성장되었고, 성장된 ZnO 나노선은 2-methyl imidazole과 methanol이 포함된 고용체에 넣고 폐쇄된 압력용기 속에서 가열시켜 얻게 된다. 이렇게 얻어진 ZIF-8@ZnO 나노선의 ZIF-8 멤브레인은 분자 체 구조(molecular sieving structure)를 갖게 되며, 이들의 pore 크기는 약 $3.4{\AA}$을 갖는다. 따라서 이보다 더 큰 동적 직경을(kinetic diameter) 갖는 가스 종은 이 멤브레인을 통과할 수 없음을 나타내므로 제작된 시편은 $H_2$(kinetic diameter : $2.89{\AA}$), $C_7H_8$(kinetic diameter : $5.92{\AA}$), 그리고 $C_6H_6$(kinetic diameter : $5.27{\AA}$) 가스들을 각각 사용함으로써 ZIF-8@ZnO 나노선의 센서 특성을 조사했으며, 보다 정확한 비교를 위해 순수한 ZnO 나노선 역시 동일한 조건에서 측정되었다. 결과를 통해, 수소 가스를 제외한 다른 가스들에 대해서는 반응을 하지 않고, 오직 수소 가스에 대해서만 반응을 나타냈으며, 순수 ZnO 나노선의 수소 감응도보다 낮은 감응도를 나타내었다. 이는 멤브레인 쉘 층을 형성함으로써 ZnO 나노선의 표면적이 감소해 가스 분자와의 접촉점을 감소시키기 때문이라고 판단된다. 이와 같은 MOF 멤브레인의 캡슐화 전략은 가스센서뿐 아니라 바이오 센서 및 광촉매 등과 같은 이온 선택성을 필요로 하는 다양한 응용분야에 적용될 수 있을 것으로 기대된다.

• 한국재료학회지
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• 제22권4호
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• pp.180-184
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• 2012

Nanostructures of ZnO, such as nanowires, nanorods, nanorings, and nanobelts have been actively studied and applied in electronic or optical devices owing to the increased surface to volume ratio and quantum confinement that they provide. ZnO seed layer (about 40 nm thick) was deposited on Si(100) substrate by RF magnetron sputtering with power of 60 W for 5 min. ZnO nanorods were grown on ZnO seed layer/Si(100) substrate at $95^{\circ}C$ for 5 hr by hydrothermal method with concentrations of $Zn(NO_3)_2{\cdot}6H_2O$ [ZNH] and $(CH_2)_6N_4$ [HMT] precursors ranging from 0.02M to 0.1M. We observed the microstructure, crystal structure, and photoluminescence of the nanorods. The ZnO nanorods grew with hexahedron shape to the c-axis at (002), and increased their diameter and length with the increase of precursor concentration. In 0.06 M and 0.08 M precursors, the mean aspect ratio values of ZnO nanorods were 6.8 and 6.5; also, ZnO nanorods had good crystal quality. Near band edge emission (NBE) and a deep level emission (DLE) were observed in all ZnO nanorod samples. The highest peak of NBE and the lower DLE appeared in 0.06 M precursor; however, the highest peak of DLE and the lower peak of NBE appeared in the 0.02 M precursor. It is possible to explain these phenomena as results of the better crystal quality and homogeneous shape of the nanorods in the precursor solution of 0.06 M, and as resulting from the bed crystal quality and the formation of Zn vacancies in the nanorods due to the lack of $Zn^{++}$ in the 0.02 M precursor.

• 한국진공학회지
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• 제20권6호
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• pp.395-402
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• 2011

원자힘 현미경을 이용하여 실리콘 기판 위에 증착된 실리콘 나노선과 리튬화된 실리콘 나노선의 나노기계적 성질을 연구했다. 금 촉매를 사용하여 스테인리스 기판 위에서 증기-액체-고체 과정을 통해 실리콘 나노선을 합성하였다. 완전히 리튬화된 실리콘 나노선을 얻기 위해서 전기 화학적 방법을 사용했고, 이를 실리콘 기판 위에 증착하였다. 접촉모드 원자힘 현미경으로 측정된 표면 거칠기는 실리콘 나노선에서 $0.65{\pm}0.05$ nm에 비해 리튬화된 실리콘 나노선에서 $1.72{\pm}0.16$ nm으로 더 큰 값을 보여주었다. 탐침과 표면 사이의 접착력에서 리튬화의 영향을 조사하기 위해 힘 분광기법을 사용했다. 실리콘 나노선의 접착력이 실리콘 기판과 ~60 nN으로 흡사한 반면에, 리튬화된 실리콘 나노선은 ~15 nN으로 더 작은 값을 나타냈다. 또한, 탄성적으로 부드러운 무정형 구조 때문에 국부적 탄성 스프링 상수도 실리콘 나노선 66.30 N/m보다 완전히 리튬화된 실리콘 나노선이 16.98 N/m으로 상대적으로 작았다. 실리콘 나노선과 완전히 리튬화된 실리콘 나노선에서 탐침과 표면 사이에 마찰력의 수직항력 의존성과 스캔 속도 의존성을 조사하기 위하여 각 0.5~4.0 Hz와 0.01~200 nN으로 측정했다. 본 연구에서 실리콘과 리튬화된 실리콘의 기계적 성질에 관련된 접착력과 마찰력의 경향성이 보여졌고 이러한 방향의 연구는 충-방전 동안 리튬화된 나노수준의 영역의 화학적 맵핑에 응용성을 보여준다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.244.1-244.1
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• 2015

The Ag Nanowire is one of the materials that are widely studied as alternatives to ITO and is available for large area, low cost process and the flexible transparent electrode. However, Ag nanowire can have the problem of a lack of stability at high temperatures, making this impossible to form a film. Using a structure of ITO/AgNW/ITO in photodetector device, we improved the properties of the ITO in the IR region and improved the thermal stability of the AgNW. The structure of ITO/AgNW/ITO has a high transmittance value of 89% at a wavelength of 900 nm and provide a good electrical property. The AgNWs embedded ITO film has a high transmittance, this is because of the light scattering from the AgNW. The thermal stability of the developed ITO/AgNWs/ITO films were investigated and found AgNWs embedded ITO films posses considerable high stability compared to the solo AgNWs on the Si surface. The ITO/AgNWs/ITO device showed a improved photo-response ratio compared to those of the conventional TC device in IR region. This is attributed to the high transmittance and low sheet resistance. We suggest an effective design scheme for IR-sensitive photodetection by using an AgNW embedded ITO.

• 한국재료학회지
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• 제20권11호
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.446-446
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• 2011

One dimensional (1-D) structures of ZnO nanorods are promising elements for future optoelectronic devices. However there are still many obstacles in fabricating high-quality p-type ZnO up to now. In addition, it is limited to measure the degree of the doping concentration and carrier transport of the doped 1-D ZnO with conventional methods such as Hall measurement. Here we demonstrate the measurement of the electronic properties of p- and n-doped ZnO nanorods by the Kelvin probe force microscopy (KPFM). Vertically aligned ZnO nanorods with intrinsic n-doped, As-doped p-type, and p-n junction were grown by vapor phase epitaxy (VPE). Individual nanowires were then transferred onto Au films deposited on Si substrates. The morphology and surface potentials were measured simultaneously by the KPFM. The work function of the individual nanorods was estimated by comparing with that of gold film as a reference, and the doping concentration of each ZnO nanorods was deduced. Our KPFM results show that the average work function difference between the p-type and n-type regions of p-n junction ZnO nanorod is about ~85meV. This value is in good agreement with the difference in the work function between As-doped p- and n-type ZnO nanorods (96meV) measured with the same conditions. This value is smaller than the expected values estimated from the energy band diagram. However it is explained in terms of surface state and surface band bending.