• Journal of Marine Bioscience and Biotechnology
• /
• v.10 no.2
• /
• pp.34-43
• /
• 2018

Silicon has become of increasing importance as the basic element of many high-technology products. Its synthesis is very difficult requiring high temperature solid-state reactions (> $1000^{\circ}C$) or lower temperature methods ($100-200^{\circ}C$) involving hydrothermal and solvothermal reactions under extreme pH conditions. In nature, on the other hand, a wide range of living organisms have collectively evolved the means of biosilicification at the astounding rate of gigatons/year. This is impressive because biosilicification in these organisms occurs under mild physiological conditions. Marine sponges possess the ability to sequester soluble silicon sources from their environments and assemble them into intricate 3D architecture. The advent of molecular biology has recently made it possible to glean molecular information about biosilicification from these systems and it turned out that enzyme silicatein is the core of biosilicification. In this review, biosilicification regulated by silicatein and its mechanism are described. Also, production of silicatein through recombinant technology and several applications of recombinant silicatein are described including immobilization of silicatein, formation of Au or Ag nanoparticles on nanowires, nanolithography approaches, core-shell materials, encapsulation, bone replacement materials, and microstructured optical fibers.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.289-289
• /
• 2013

While there are plenty of studies on synthesizing semiconducting germanium nanowires (Ge NWs) by vapor-liquid-solid (VLS) process, it is difficult to inject dopants into them with uniform dopants distribution due to vapor-solid (VS) deposition. In particular, as precursors and dopants such as germane ($GeH_4$), phosphine ($PH_3$) or diborane ($B_2H_6$) incorporate through sidewall of nanowire, it is hard to obtain the structural and electrical uniformity of Ge NWs. Moreover, the drastic tapered structure of Ge NWs is observed when it is synthesized at high temperature over $400^{\circ}C$ because of excessive VS deposition. In 2006, Emanuel Tutuc et al. demonstrated Ge NW pn junction using p-type shell as depleted layer. However, it could not be prevented from undesirable VS deposition and it still kept the tapered structures of Ge NWs as a result. Herein, we adopt $C_2H_2$ gas in order to passivate Ge NWs with carbon sheath, which makes the entire Ge NWs uniform at even higher temperature over $450^{\circ}C$. We can also synthesize non-tapered and uniformly doped Ge NWs, restricting incorporation of excess germanium on the surface. The Ge NWs with carbon sheath are grown via VLS process on a $Si/SiO_2$ substrate coated 2 nm Au film. Thin Au film is thermally evaporated on a $Si/SiO_2$ substrate. The NW is grown flowing $GeH_4$, HCl, $C_2H_2$ and PH3 for n-type, $B_2H_6$ for p-type at a total pressure of 15 Torr and temperatures of $480{\sim}500^{\circ}C$. Scanning electron microscopy (SEM) reveals clear surface of the Ge NWs synthesized at $500^{\circ}C$. Raman spectroscopy peaked at about ~300 $cm^{-1}$ indicates it is comprised of single crystalline germanium in the core of Ge NWs and it is proved to be covered by thin amorphous carbon by two peaks of 1330 $cm^{-1}$ (D-band) and 1590 $cm^{-1}$ (G-band). Furthermore, the electrical performances of Ge NWs doped with boron and phosphorus are measured by field effect transistor (FET) and they shows typical curves of p-type and n-type FET. It is expected to have general potentials for development of logic devices and solar cells using p-type and n-type Ge NWs with carbon sheath.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.399-399
• /
• 2008

Synthesis and characterization of ZnO structure such as nanowires, nanorods, nanotube, nanowall, etc. have been studied to multifunctional application such as optical, nanoscale electronic and chemical devices because it has a room-temperature wide band gap of 3.37eV, large exiton binding energy(60meV) and various properties. Various synthesis methods including chemical vapor deposition (CVD), physical vapor deposition, electrochemical deposition, micro-emulsion, and hydrothermal approach have been reported to fabricate various kinds of ZnO nanostructures. But some of these synthesis methods are expensive and difficult of mass production. Wet chemical method has several advantage such as simple process, mass production, low temperature process, and low cost. In the present work, ZnO nanorods are deposited on ITO/glass substrate by simple wet chemical method. The process is perfomed by two steps. One-step is deposition of ZnO seeds and two-step is growth of ZnO nanorods on substrates. In order to form ZnO seeds on substrates, mixture solution of Zn acetate and Methanol was prepared.(one-step) Seed layers were deposited for control of morpholgy of ZnO seed layers by spin coating process because ZnO seeds is deposited uniformly by centrifugal force of spin coating. The seed-deposited samples were pre-annealed for 30min at $180^{\circ}C$ to enhance adhesion and crystallinnity of ZnO seed layer on substrate. Vertically well-aligned ZnO nanorods were grown by the "dipping-and-holding" process of the substrates into the mixture solution consisting of the mixture solution of DI water, Zinc nitrate and hexamethylenetetramine for 4 hours at $90^{\circ}C$.(two-step) It was found that density and morphology of ZnO nanorods were controlled by manipulation of ZnO seeds through rpm of spin coating. The morphology, crystallinity, optical properties of the grown ZnO nanostructures were carried out by field-emission scanning electron microscopy, high-resolution electron microscopy, photoluminescence, respectively. We are convinced that this method is complementing problems of main techniques of existing reports.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.430.1-430.1
• /
• 2016

We present the concept of reducible fugitive material that conformally surrounds core Cu nanowire (NW) to fabricate transparent conducting electrode (TCE). Reducing atmosphere can corrodes/erodes the underlying/surrounding layers and might cause undesirable reactions such impurity doing and contamination, so that hydrogen-/forming gas based annealing is impractical to make device. In this regards, we introduce novel reducible shell conformally surrounding indivial CuNW to provide a protection against the oxidation when exposed to both air and solvent. Uniform copper lactate shell formation is readily achievable by injecting lactic acid to the CuNW dispersion as the acid reacts with the surface oxide/hydroxide or pure copper. Cu lactate shell prevents the core CuNW from the oxidation during the storage and/or film formation, so that the core-shell CuNW maintains without signficant oxidation for long time. Upon simple thermal annealing under vacuum or in nitrogen atmosphere, the Cu lactate shell is easily decomposed to pure Cu, providing an effective way to produce pure CuNW network TCE with typically sheet resistance of $19.8{\Omega}/sq$ and optical transmittance of 85.5% at 550 nm. Our reducible copper lactate core-shell Cu nanowires have the great advantage in fabrication of device such as composite transparent electrodes or solar cells.

• Korean Journal of Materials Research
• /
• v.20 no.4
• /
• pp.199-203
• /
• 2010

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at $400^{\circ}C$ under an $N_2/O_2$ atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from $400^{\circ}C$ to $600^{\circ}C$. The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under $500^{\circ}C$, while nanowire structures begin to form on the beads above $600^{\circ}C$. The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of $2.0\;V/{\mu}m$ was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.4
• /
• pp.166-171
• /
• 2006

[ $Cu_2O$ ] and Cu have been synthesized from the layered organic-inorganic hybrid, $Cu_2(OH)_3(CH_3COO){\cdot}H_2O$, assisted by microwave irradiation. $Cu_2O$ is formed in aqueous glucose solution, while metallic Cu is formed in ethylene glycol by reduction of $Cu_2(OH)_3(CH_3COO){\cdot}H_2O$. The influence of microwave irradiation time and concentration of glucose on $Cu_2O$ particles formation and growth has been examined. The morphologies of $Cu_2O$ particles change from spheres with a few fm size to nanowires with diameter of 40 nm as increasing the microwave irradiation times.

• Applied Chemistry for Engineering
• /
• v.30 no.6
• /
• pp.694-697
• /
• 2019

In recent years, titanium dioxide powders were produced as nanoparticles or nanowires or nanotubes in one-dimensional structure, and mesoporous spheres in 3-D to improve their crystallinities, which were further used as photo-electrode materials and for preventing photo-aging. In this study, a nano sol composed of titanium dioxide exhibiting a high crystallinity was synthesized using n-alcohol as a solvent. The crystallinity of the nano sol was confirmed by FE-SEM, and XRD, while the UV blocking rate confirmed by UV-Vis spectrometry results. Changes in the crystallinity were investigated by varying the types of solvents such as butanol, propanol and ethanol. The synthesized particle sizes were from 200 to 250 nm, and the optical transmittance showed a high blocking rate in the UVB and UVA range. It is expected that a high transmittance at 550 nm wavelength can increase the photoelectric conversion efficiency of solar cells and the UV blocking efficiency.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.580-580
• /
• 2012

Heterostructures has unique and important properties, which may be helpful for finding many potential applications in the field of electronic, thermoelectric, and optoelectronic devices. We synthesized CdTe/Te core-shell heterostructures by vapor-solid process at low temperatures using a quartz tube furnace. Two step vapor-solid processes were employed. First, various tellurium structures such as nanowires, nanorods, nanoneedles, microtubes and microrods were synthesized under various deposition conditions. These tellurium nanostructures were then used as substrates in the second step to synthesize the CdTe/Te core-shell heterostructures. Using this method, various sizes, shapes and types of CdTe/Te core-shell structures were fabricated under a range of conditions. These structures were analysed by scanning electron microscopy, high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. The vapor phase process at low temperatures appears to be an efficient method for producing a variety of Cd/Te hetero-nanostructures. In addition, the hetero-nanostructures can be tailored to the needs of specific applications by deliberately controlling the synthetic parameters.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2016.11a
• /
• pp.96-96
• /
• 2016

나노섬유(nanofiber), 나노선(nanowire), 그리고 나노튜브(nanotube)와 같은 1차원 구조의(one-dimensional structure) 나노재료는 벌크(bulk) 및 박막(film) 재료와는 다르게 물리적, 화학적으로 특이한 성질을 가지고 있으며, 이러한 성질은 나노재료의 구조, 형상, 크기 등에 큰 영향을 받는다. 첫 째, 전기방사(electrospinning) 공정을 이용한 나노섬유의 합성; 용액의 특성, 전기장 세기, 방사시간 등의 변수를 조절하게 되면 방출되는 재료의 형상을 입자 혹은 섬유상의 형태로 얻을 수 있으며, 전기방사를 통해 합성된 나노재료의 소결 온도 및 시간을 달리함으로써 나노입자의 크기를 조절할 수 있다. 또한, 템플레이트 합성법(template synthesis) 및 이중노즐(coaxial nozzle)을 이용해 속이 빈 형태인 중공(hollow) 구조의 나노섬유를 얻을 수 있으며, 전기방사에 사용되는 전구물질에 원하는 금속 및 산화물을 첨가함으로써 복합체(composite) 나노섬유를 얻을 수 있다. 둘 째, VLS(Vapor-Liquid-Solid) 공정을 이용한 나노선의 성장; 온도, 압력, 전구물질의 양, 그리고 시간 등의 변수를 조절하게 되면 원하는 직경 및 길이를 갖는 나노선을 성장시킬 수 있다. 그리고 ALD(Atomic Layer Deposition)를 이용해 나노선에 추가적인 층을 형성함으로써 코어-셀 구조를 형성할 수 있으며, 감마선, UV와 같은 공정을 이용해 귀금속 촉매를 나노선에 기능화 시킬 수도 있다. 코어-셀 구조를 갖는 나노선/나노섬유는 코어 혹은 셀 층의 전자나 홀의 이동을 유발하여 전자공핍층(electron depletion layer) 또는 정공축적층(hole accumulation layer)을 확대 및 축소시켜 센서의 초기저항을 증가시키거나 감소시키는 역할로써 이용되고 있으며, 특히, 셀 층의 두께가 셀 층 재료의 Debye length와 유사한 크기를 갖게 되면, 셀 층은 완전공핍층(fully depleted layer)을 형성해 최대의 감도를 나타낼 수 있다. 본 연구에서는 다양한 제조 공정을 통해 제작될 수 있는 1차원 나노-구조물을 가스센서에 적용하는 사례들을 소개하고, 이러한 가스센서의 감응성능을 향상시키기 위한 방법의 한 가지로 원자층증착법으로 나노선/나노섬유의 표면에 셀층을 형성하여 감응성 향상 메커니즘 및 관련 주요 변수들을 조사하고자 한다.

• Korean Journal of Materials Research
• /
• v.33 no.10
• /
• pp.377-384
• /
• 2023

Exploring earth-abundant, highly effective and stable electrocatalysts for electrochemical water splitting is urgent and essential to the development of hydrogen (H₂) energy technology. Iron-cobalt layered double hydroxide (FeCo-LDH) has been widely used as an electrocatalystfor OER due to its facile synthesis, tunable components, and low cost. However, LDH synthesized by the traditional hydrothermal method tends to easily agglomerate, resulting in an unstable structure that can change or dissolve in an alkaline solution. Therefore, studying the real active phase is highly significant in the design of electrochemical electrode materials. Here, metal-organic frameworks (MOFs) are used as template precursors to derive FeCo-LDH from different iron sources. Iron salts with different anions have a significant impact on the morphology and charge transfer properties of the resulting materials. FeCo-LDH synthesized from iron sulfate solution (FeCo-LDH-SO₄) exhibits a hybrid structure of nanosheets and nanowires, quite different from other electrocatalysts that were synthesized from iron chloride and iron nitrate solutions. The final FeCo-LDH-SO₄ had an overpotential of 247 mV with a low Tafel-slope of 60.6 mV dec^-1 at a current density of 10 mA cm^-2 and delivered a long-term stability of 40 h for the OER. This work provides an innovative and feasible strategy to construct efficient electrocatalysts.