• Advances in nano research
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• v.2 no.3
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• pp.157-172
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• 2014

The three-dimensional Nano-Electronic Modeling toolkit (NEMO 3-D) is an open source software package that allows the atomistic calculation of single-particle electronic states and optical response of various semiconductor structures including bulk materials, quantum dots, impurities, quantum wires, quantum wells and nanocrystals containing millions of atoms. This paper, first, describes a software module introduced in the NEMO 3-D toolkit for the calculation of electronic bandstructure and interband optical transitions in nanowires having wurtzite crystal symmetry. The energetics (Hamiltonian) of the quantum system under study is described via the tight-binding (TB) formalism (including $sp^3$, $sp^3s^*$ and $sp^3d^5s^*$ models as appropriate). Emphasis has been given in the treatment of surface atoms that, if left unpassivated, can lead to the creation of energy states within the bandgap of the sample. Furthermore, the developed software has been validated via the calculation of: a) modulation of the energy bandgap and the effective masses in [0001] oriented wurtzite nanowires as compared to the experimentally reported values in bulk structures, and b) the localization of wavefunctions and the optical anisotropy in GaN/AlN disk-in-wire nanowires.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.328.2-328.2
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• 2014

Semiconductor nanowires (NWs) have attracted research interests due to the distinct physical properties that can lead to variousoptical and electrical applications. In this paper, we have grown InAs NWs viagold (Au)-assisted vapor-liquid-solid (VLS) and catalyst-free vapor-solid (VS) mechanisms and investigated on the p-type doping profile of the NWs. Metal-organic chemical vapor deposition (MOCVD) is used for the growth of the NWs. Trimethylindium (TMIn) and arsine (AsH3) were used for the precursor and diethyl zinc (DEZn) was used for the p-type doping source of the NWs. The effectiveness of p-type doping was confirmed by electrical measurement, showing an increase of the electron density with the DEZn flow. The structural properties of the InAs NWs were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, we characterize atomic distribution of InAs NWs using energy-dispersive X-ray spectroscopy (EDX) analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.421.1-421.1
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• 2014

Top-down processes based on photolithography technology have been developed by using light sources with short wavelength, however, the processes are expected to meet their limits in higher integration of semiconductor integrated circuits. To overcome the limits, researches on bottom-up processes have been proceeded. One of those, fabrication of nanodevices by using nanoparticles has been on research. But it is difficult to align nanoparticles at appropriate positions. To resolve this, studies has been proceeded to form nanowires by bonding DNA molecules which have self-assembly property and positive-charged functionalized gold nanoparticles. There are negative-charged phosphates in backbones of DNA molecules. By using the attractive force between the negative charge of the phosphates and the positive charge of gold nanoparticles, the Au-DNA nanowires are made. However, bonding Au nanoparticles only on DNA molecules, not other nanoparticles, is to be solved. So we studied to resolve this problem. In the formation of Au nanoparticles, we changed the charge of Au nanoparticles by adding HCl to control pH of the functionalized nanoparticles, measured zeta potential. Then we bonded the nanoparticles and DNA molecules and made observation by using FE-SEM and AFM.

• Korean Journal of Materials Research
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• v.25 no.7
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• pp.358-363
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• 2015

We present an excellent detection for nitrogen monoxide (NO) gas using polycrystalline ZnO wire-like films synthesized via a simple method combined with sputtering of Zn metallic films and subsequent thermal oxidation of the sputtered Zn nanowire films in dry air. Structural and morphological characterization revealed that it would be possible to synthesize polycrystalline hexagonal wurtzite ZnO films of a wire-like nanostructure with widths of 100-150 nm and lengths of several microns by controlling the sputtering conditions. It was found from the gas sensing measurements that the ZnO wire-like thin film gas sensor showed a significantly high response, with a maximum value of 29.2 for 2 ppm NO at $200^{\circ}C$, as well as a reversible fast response to NO with a very low detection limit of 50 ppb. In addition, the ZnO wire-like thin film gas sensor also displayed an NO-selective sensing response for NO, $O_2$, $H_2$, $NH_3$, and CO gases. Our results illustrate that polycrystalline ZnO wire-like thin films are potential sensing materials for the fabrication of NO-sensitive high-performance gas sensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.409-409
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• 2012

최근 나노크기의 미세구조 가공기술이 발달함에 따라 다양한 응용을 위한 나노소재/구조가 활발히 연구 되고 있다[1]. 그 중에서 실리콘 나노선은 태양전지, 메모리, 트랜지스터 그리고 광 공진기에 쓰일 수 있는 소재로서 기존의 실리콘 가공기술을 바로 사용할 수 있을 뿐 아니라[2], 비용 면에서 탁월한 잇점이 있기 때문에 주목 받고 있는 소재이다. 실리콘 나노선의 물리적 특성을 연구하기 위한 많은 연구가 진행되었지만, 매우 작은 크기와 높은 표면적-부피비율로 인해 생긴 독특한 특징을 완전히 이해하기에는 아직 부족한 점이 많다. 실리콘 나노선의 전류-전압특성에 영향을 미치는 요소는 도핑농도, 표면상태, 채널의 크기 등으로 다양한데, 이번 연구에서는 실리콘 나노선의 표면환경이 공기와 물 두 종류로 매질에 접하고 있을 경우에 대하여 각각 전류-전압을 측정하였다. 물이 공기와 다른 점은 크게 두 가지로 볼 수 있다. 첫째로 물의 경우에는 물에 용해된 수소이온과의 화학반응을 통하여 실리콘 표면전하가 유도되며 pH 값에 민감하게 변화한다. 둘째로 물의 유전율은 공기의 80배로서 표면부근에서의 전기장분포가 많이 왜곡된다. 이를 위하여 SOI를 기반으로 채널길이 $5{\mu}s$, 두께 40 nm, 너비 100 nm인 실리콘 나노선을 일반적인 반도체공정을 사용하여 제작하였다. 나노선의 전기적 특성 실험은 Semiconductor Parameter Analyzer (Agilent, 4155C)를 사용하여 전류-전압특성을 표면 상태를 변화시키면서 측정하였다. 실험을 통해 실리콘 나노선은 물과 공기 두 가지 표면환경에 따라 전류-전압특성이 확연히 변화하는 것을 볼 수 있었다. 동일한 전압 바이어스에서 표면에 물이 있을 때가 공기 있을 때 보다 훨씬 증가한 전류를 얻을 수 있었고(3V에서 약 2배), 비선형적인 전류-전압특성이 나타남을 관찰하였다. 본 발표에서는 이러한 실험결과를 표면에서의 전하와 정전기적인 효과로서 정성적으로 설명하고, 전산모사결과와 비교분석 하고자 한다.

• Journal of Adhesion and Interface
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• v.23 no.4
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• pp.116-121
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• 2022

OFET have require fine patterning technology for organic semiconductor solution process to be used in actual electronics. In this study, we compared and analyzed the soft lithography method which can form fine patterns more than the conventional spin coating method in order to confirm that it can have better electrical characteristics. The soft lithography method produced a flexible master mold using nano patterns on compact disc surfaces and obtained a 650 nm wide 2,7-Dioctyl [1] benzothieno [3,2-b] [1] benzo thiophene (C_8-BTBT) nanowires. As a result, the field-effect mobility of devices fabricated by the spin coating method was 0.0036 cm²/Vs and mobility of devices produced by soft lithography method was 0.086 cm²/Vs, which was about 20 times higher than spin-coated devices and has better electrical performance.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.993-994
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• 2008

Electrochromic (EC) devices are capable of reversibly changing their optical properties upon charge injection and extraction induced by the external voltage. The characteristics of the EC device, such as low power consumption, high coloration efficiency, and memory effects under open circuit status, make them suitable for use in a variety of applications including smart windows and electronic papers. Coloration due to reduction or oxidation of redox chromophores can be used for EC devices (e-paper), but the switching time is slow (second level). Recently, with increasing demand for the low cost, lightweight flat panel display with paper-like readability (electronic paper), an EC display technology based on dye-modified $TiO_2$ nanoparticle electrode was developed. A well known organic dye molecule, viologen, was adsorbed on the surface of a mesoporous $TiO_2$ nanoparticle film to form the EC electrode. On the other hand, ZnO is a wide bandgap II-VI semiconductor which has been applied in many fields such as UV lasers, field effect transistors and transparent conductors. The bandgap of the bulk ZnO is about 3.37 eV, which is close to that of the $TiO_2$ (3.4 eV). As a traditional transparent conductor, ZnO has excellent electron transport properties, even in ZnO nanoparticle films. In the past few years, one-dimension (1D) nanostructures of ZnO have attracted extensive research interest. In particular, 1D ZnO nanowires renders much better electron transportation capability by providing a direct conduction path for electron transport and greatly reducing the number of grain boundaries. These unique advantages make ZnO nanowires a promising matrix electrode for EC dye molecule loading. ZnO nanowires grow vertically from the substrate and form a dense array (Fig. 1). The ZnO nanowires show regular hexagonal cross section and the average diameter of the ZnO nanowires is about 100 nm. The cross-section image of the ZnO nanowires array (Fig. 1) indicates that the length of the ZnO nanowires is about $6\;{\mu}m$. From one on/off cycle of the ZnO EC cell (Fig. 2). We can see that, the switching time of a ZnO nanowire electrode EC cell with an active area of $1\;{\times}\;1\;cm^2$ is 170 ms and 142 ms for coloration and bleaching, respectively. The coloration and bleaching time is faster compared to the $TiO_2$ mesoporous EC devices with both coloration and bleaching time of about 250 ms for a device with an active area of $2.5\;cm^2$. With further optimization, it is possible that the response time can reach ten(s) of millisecond, i.e. capable of displaying video. Fig. 3 shows a prototype with two different transmittance states. It can be seen that good contrast was obtained. The retention was at least a few hours for these prototypes. Being an oxide, ZnO is oxidation resistant, i.e. it is more durable for field emission cathode. ZnO nanotetropods were also applied to realize the first prototype triode field emission device, making use of scattered surface-conduction electrons for field emission (Fig. 4). The device has a high efficiency (field emitted electron to total electron ratio) of about 60%. With this high efficiency, we were able to fabricate some prototype displays (Fig. 5 showing some alphanumerical symbols). ZnO tetrapods have four legs, which guarantees that there is one leg always pointing upward, even using screen printing method to fabricate the cathode.