• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.386-386
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• 2011

sol-gel 및 hydrothermal growth method를 이용한 zinc oxide nanorod는 제작 시 고가의 장비가 필요치 않기에 저비용 대면적 박막을 제작하는데 적합하지만 rod들의 array 및 density 조절에서 어려움을 가지고 있다. 본 연구에서는 이러한 nanorod array 형상 조절을 위하여 zinc oxide seed layer 형성 과정 중 precursor solution에 이종 나노 입자를 첨가하였다. 첨가한 seed precursor solution을 spin coating한 이후에 후처리 하여 hydrothermal method를 이용해 성장시켰다. 합성한 rod들을 optic과 FE-SEM으로 측정해 rod들의 density 변화를 확인할 수 있었다.

• Journal of the Korean Electrochemical Society
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• v.12 no.1
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• pp.40-46
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• 2009

We present a method for spatially selective immobilization of functional materials, such as proteins and nanoparticles, onto pre-activated silicon surfaces by electrochemical reaction. Carboxymethylbenzendiazonium (CMBD) cations, being adsorbable on silicon surfaces through electrochemically reductive deposition, is used as an anchor molecule to prepare the pre-activated silicon surfaces. It is demonstrated that the use of BD reaction is very efficient for the selective immobilization because the functional materials are immobilized exclusively onto the pre-adsorbed CMBD region. The method is applied to immobilize gold nanoparticles on the selected nanowire of the nanowire array.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.384-384
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• 2011

양자점 감응형 태양전지는 염료감응형 태양전지와 비슷한 구조를 가지지만, 유기물 염료를 대신하여 무기물 양자점을 사용함으로서 기존 유기물 염료가 가지는 한계점을 극복할 수 있다. 양자점을 광감응 염료로 사용하는 경우 양자제한효과(quantum confinement effect)에 의해 양자점의 사이즈조절만으로 밴드갭을 조절할 수 있어 광학적 특성 조절이 용이하며, 유기물 염료보다 광흡수 능력도 뛰어나다. 더불어, 하나의 광자를 흡수하여 두개 이상의 전자-정공쌍을 만들 수 있는(multiple exciton generation) 가능성이 있어 기존 태양전지가 가지는 이론적 한계효율(Shockley-Queisser limit)을 뛰어넘을 수 있다. 본 연구에서는 고효율의 양자점 감응형 태양전지 개발을 위해, ZnO 나노선 구조에 CdS, CdSe 양자점을 증착한 CdSe/CdS/ZnO 나노선 헤테로구조를 수열합성법으로 합성하였다. 증착한 CdSe/CdS 양자점이 태양광의 가시광 전 영역을 흡수하여 전자-정공을 생성하며, 세 물질 간의 밴드구조를 통해 양자점에서 생성된 전자가 ZnO 나노선으로 포집되고, 바닥전극으로 직접연결이 되어있는 1차원의 나노선 구조를 통해 전자를 효율적으로 운반할 수 있다.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.217-222
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• 2020

The design and fabrication of catalysts with low-cost and high electrocatalytic activity for the oxygen evolution reaction (OER) have remained challenging because of the sluggish kinetics of this reaction. The key to the pursuit of efficient electrocatalysts is to design them with high surface area and more active sites. In this work, we have successfully synthesized a highly stable and active NiCo₂S₄ nanowire array on a Ni-foam substrate (NiCo₂S₄ NW/NF) via a two-step hydrothermal synthesis approach. This NiCo₂S₄ NW/NF exhibits overpotential as low as 275 mV, delivering a current density of 20 mA cm^-2 (versus reversible hydrogen electrode) with a low Tafel slope of 89 mV dec^-1 and superior long-term stability for 20 h in 1 M KOH electrolyte. The outstanding performance is ascribed to the inherent activity of the binder-free deposited, vertically aligned nanowire structure, which provides a large number of electrochemically active surface sites, accelerating electron transfer, and simultaneously enhancing the diffusion of electrolyte.

• Korean Journal of Materials Research
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• v.32 no.6
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• pp.307-312
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• 2022

Metal halide perovskite (MHP) nanocrystals (NCs) have emerged as promising materials for various optoelectronic applications including photovoltaics, light-emitting devices, and photodetectors because of their high absorption coefficient, high diffusion length, and photoluminescence quantum yield. However, understanding the morphological evolution of the MHP NCs as well as their controlled assembly into optoelectronic devices is still challenging and will require further investigation of the colloidal chemistry. In this study, we found that the amount of n-octylamine (the capping agent) plays a crucial role in inducing further growth of the MHP NCs into one-dimensional nanowires during the aging process. In addition, we demonstrate that the dielectrophoresis process can permit self-alignment of the MHP nanowires with uniform distribution and orientation on interdigitated electrodes. A strong light-matter interaction in the MHP NWs array was observed under UV illumination, indicating the photo-induced activation of their luminescence and electrical current in the self-aligned MHP nanowire arrays.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.275-275
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• 2013

Osteoblast is one of cells related with osseointegration and many research have conducted the adhesion of osteoblast onto the surface of implant. In the osseointegration, biocompatibility of the implant and cell adhesion to the surface are important factors. The researches related to cell adhesion have a direction from micro-scaled surface roughness to nano-scaled surface roughness with advancing nanotechnology. A cell reacts and sense to stimuli from extracellular matrix (ECM) and topography of the ECM [1]. Thus, for better osseointegration, we should provide an environment similar to ECM. In this study, we synthesize TiO2 nanowires using hydrothermal reaction because TiO2 provides inertness to titanium on its surface and enables it used as an implant material for the orthopedic treatment such as fixation of the bone fracture [2]. Ti substrate is immersed into NaOH aqueous solution. The solution are heated at $140{\sim}200^{\circ}C$ for various time (10~720 minutes). After heat treatment, we take out the sample and immerse it into HCl aqueous solution for 1 hour. The acid treated sample is heated again at $500^{\circ}C$ for 3 hours [3]. Then, we culture osteoblast on the TiO2 nanowires. For investigating cell adhesion onto nanostructured surface, we conduct several tests such as MTT assay, ALP (Alkaline phosphatase) activity assay, measuring calcium expression, and so on. These preliminary results of the cell culture on the nanowires are foundation for investigating cell-material interaction especially with nanostructure interaction.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.209-218
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• 2012

Recently, the Field Programmable Stateful Logic Array (FPSLA) was proposed as one of the most promising system integration technologies which will extend the life of the Moore's law. This work is the first proposal of the FPSLA design automation flow, and the approaches to logic synthesis, synchronization, physical mapping, and automatic placement of the FPSLA designs. The synchronization at each gate for pipelining determines the x-coordinates of cells, and reduces the placement to 1-dimensional problems. The objective function and its gradients for the non-linear optimization of the net length and placement density have been remodeled for the reduced global placement problem. Also, a recursive algorithm has been proposed to legalize the placement by relaxing the density overflow of bipartite bin groups in a top-down hierarchical fashion. The proposed model and algorithm are implemented, and validated by applying them to the ACM/SIGDA benchmark designs. The output state of a gate in an FPSLA needs to be duplicated so that each fanout gate can be connected to a dedicated copy. This property has been taken into account by merging the duplicated nets into a hyperedge, and then, splitting the hyperedge into edges as the optimization progresses. This yields additional 18.4% of the cell count reduction in the most dense logic stage. The practicality of the FPSLA can be further enhanced primarily by incorporating into the logic synthesis the constraint to avoid the concentrated fains of gates on some logic stages. In addition, an efficient algorithm needs to be devised for the routing problem which is based on a complicated graph. The graph models the nanowire crossbar which is trimmed to be embedded into the FPSLA fabric, and therefore, asymmetric. These CAD tools can be used to evaluate the fabric efficiency during the architecture enhancement as well as automate the design.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.7.1-7.1
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• 2011

Nanoporous templates have been widely used for the development of new functional nanostructured materials suitable for electronics, optics, magnetism, and energy storage materials. We have prepared nanoporous templates by using thin films of mixtures of polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) and PMMA homopolymers. These templates have cylindrical nanoholes spanning the entire thickness of the film. Some applications of nanoporous templates are introduced: a) anti-reflective coating, b) the preparation of conducting polymer nanowires of poly (pyrrole), poly (3,4-ethylenedioxy-thiopene) onto a glass coated with indium-tin-oxide, and c) the separation membranes for biomaterials. We found that when the pore fraction of nanoholes in the film was ~0.68, almost zero reflectance at a specific wavelength, which can be changed with film thickness, was achieved at visible wavelengths Furthermore, ultra high density array of conducting nanowires was successfully prepared onto various substrates including flexible polymer. Due to highly alignment of polymer chain along the nanowire direction, the conductivity was much increased. Furthermore, these nanoporous films were found to be very effective for the separation of human Rhinovirus type 14 (HRV 14), major pathogen of a common cold in humans, from the buffer solution. We also found that when the pore size was effectively controlled down to 6 nm, a single file diffusion was observed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.26.1-26.1
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• 2011

We investigated the atomic layer deposition (ALD) process for nitrogen doped ZnO and the application for n-ZnO : N/p-Si (NW) coaxial hetero-junction photodetectors. ALD ZnO:N was deposited using diethylzinc (DEZ) and diluted $NH_4OH$ at $150^{\circ}C$ of substrate temperature. About 100~300 nm diameter and 5 um length of Si nanowires array were prepared using electroless etching technique in 0.108 g of $AgNO_3$ melted 20 ml HF liquid at $75^{\circ}C$. TEM images showed ZnO were deposited on densely packed SiNW structure achieving extraordinary conformality. When UV (360 nm) light was illuminated on n-ZnO:N/p-SiNW, I-V curve showed about three times larger photocurrent generation than film structure at 10 V reverse bias. Especially, at 660 nm wave length, the coaxial structure has 90.8% of external quantum efficiency (EQE) and 0.573 A/W of responsivity.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.623-626
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• 2010

We synthesized ZnO nanowires patterned on Si substrate and investigated the field emission properties of the nanowires. Firstly, Au catalyst layers were fabricated on Si substrate by photo-lithography and lift-off process. The diameter of Au pattern was $50\;{\mu}m$ and the pattern was arrayed as $4{\times}4$. ZnO nanowires were grown on the Au catalyst pattern by the aid of Au liquid phase. The orientation of the ZnO nanowires was vertical on the whole. Sufficient brightness was obtained when the electric field was $5.4\;V/{\mu}m$ and the emission current was $5\;mA/cm^2$. The threshold electric field was $5.4\;V/{\mu}m$ in the $4{\times}4$ array of ZnO nanowires, which is quite lower than that of the nanowires grown on the flat Si substrate. The lower threshold electric field of the patterned ZnO nanowires could be attributed to their vertical orientation of the ZnO nanowires.