• 센서학회지
• /
• 제19권6호
• /
• pp.462-468
• /
• 2010

A low power gas sensor with microheater was fabricated by MEMS technology. In order to heat up the gas sensing material to a operating temperature, a platinum(Pt) micro heater was built on to the micromachined Si substrate. The width and gap of microheater were $20\;{\mu}m$ and $4.5\;{\mu}m$, respectively. ZnO nanowhisker arrays were fabricated on a sensor device by hydrothermal method. The sensor device was deposited with ZnO seeds using PLD systems. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growthing ZnO nanowhiskers. The power consumption to heat up the gas sensor to a operating temperature was measured and temperature distribution of sensor was analyzed by a Infrared Thermal Camera. The optimum temperature for highest sensitivity was found to be $250^{\circ}C$ although relatively high(64 %) sensitivity was obtained even at as low as $150^{\circ}C$. The power consumption was 72 mW at $250^{\circ}C$ and was only 25 mW at $150^{\circ}C$.

• 자원환경지질
• /
• 제24권3호
• /
• pp.219-226
• /
• 1991

High quality quartz crystals are grown in 0.5N NaOH + LiOH solution on the seed crystal at $370-395^{\circ}C$ and $1200-1300kg/cm^2$ condition. Growth rates are determined by the crystal thickness grown on the seed crystals with Z(0001) and X($11\bar{2}0$) direction. Relatively high growth rate of Z(0001) direction gradually changes as the temperaure difference (${\Delta}$ Ti) between growth and dissolution zones from 25 to $10^{\circ}C$. The X axis direction is affeced by ${\Delta}$ Ti, and +X($11\bar{2}0$) direction shows a high growth rate than -X($\bar{1}\bar{1}20$) direction. According to the variation with kinds of solutions used, the crystal growth that in NaOH solution is found to be slower than that in $Na_2CO_3$ solution. However, for the case in the NaOH solution mixed with LiOH, it shows a favorable growth rate in terms of grown crystal quality.

• 한국표면공학회지
• /
• 제49권1호
• /
• pp.75-80
• /
• 2016

$In_2O_3$ nanowires were coated with $Co_3O_4$ nanoparticles to investigate the improvement of ethanol gas sensing performance compared with as-synthesized $In_2O_3$ nanowires. Scanning electron microscopy showed that the nanowires synthesized by VLS mechanism had diameters and lengths of approximately 50-100 nm and a few micrometers, respectively. $Co_3O_4$ nanoparticles produced by hydrothermal method was in the size range of a few to a few tens nm. As-synthesized and $Co_3O_4$ nanoparticles coated $In_2O_3$ nanowires sensors exhibited responses of 1.96% and 4.57%, respectively for the ethanol gas concentration of 200 ppm at $200^{\circ}C$. The underlying mechanism for the improved responses of $Co_3O_4$ nanoparticles coated $In_2O_3$ nanowires sensors is discussed.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
• /
• pp.189.2-189.2
• /
• 2013

1차원 산화아연 나노구조물은 광대역 에너지 밴드갭(~3.3 eV)과 독특한 물리적 특성을 갖고 있어, 전계효과 트랜지스터(field effect transistor), 발광다이오드(light emitting diode), 자외선 광검출기 (ultraviolet photodetector) 및 태양전지(photovoltaic cell)에 널리 이용되고 있다. 특히, 1차원 산화아연 나노구조물은 직접천이형 에너지 밴드갭(direct bandgap)을 갖고 있으며, 빛으로부터 여기된 전자가 1차원 나노구조물을 통해 향상된 이동경로를 제공할 수 있어서 차세대 자외선 광검출기 응용에 대한 연구가 활발히 진행되고 있다. 한편, 수열합성법(hydrothermal method)을 통해서 1차원 산화아연 나노구조물을 비교적 간단하고 저온공정을 통해서 합성할 수 있는데, 이를 광검출기 소자구조에 응용에서 양전극에 연결하기 위해서는 복잡하고 정교한 공정이 필요하다. 이에 본 연구에서는 수열합성법을 통해 합성된 산화아연 나노로드가 포함된 에탄올 용액을 금(Au) 패턴에 drop-casting을 통해서 간단한 방법으로 metal-semiconductor-metal (MSM) 광검출기를 제작하여 광반응 특성을 분석하였다. 또한 염료를 통해 가시광을 흡수하여 광전류(photocurrent)를 발생시킬 수 있도록 염료를 흡착한 산화아연 나노로드를 이용하여 같은 구조의 MSM 광검출기를 제작하여 가시광에 대한 광반응 특성을 관찰하였다.

• 한국표면공학회지
• /
• 제48권5호
• /
• pp.238-244
• /
• 2015

$TiO_2$ nanowires were synthesized by hydrothermal method for the application to ethanol gas sensor. $TiO_2$ nanowires were decorated with Au nanoparticles to improve the sensitivity to ethanol gas. Scanning electron microscopy and Transmission electron microscopy revealed that the synthesized nanowires had diameters and lengths of approximately 100 - 200 nm and a few micrometers, respectively. Size of the Au nanoparticles decorated on the $TiO_2$ nanowires was observed to be in the range of 10 - 20 nm. X-ray diffraction confirmed that the decorated nanowires were composed of anatase-, rutile-$TiO_2$, and Au. The sensitivities of $TiO_2$ nanowires sensors decorated with Au were approximately 1.1 - 3.65 times as high as those of as-synthesized $TiO_2$ sensors for the ethanol concentration of 5 - 100 ppm at $200^{\circ}C$. The mechanism of the improved ethanol gas sensing of the $TiO_2$ nanowires decorated with Au nanoparticles is discussed.

• 한국표면공학회지
• /
• 제49권4호
• /
• pp.382-388
• /
• 2016

NiO nanoparticles were synthesized by hydrothermal method for the application to ethanol gas sensor. They were composited with $Co_3O_4$ nanoparticles to improve the sensitivity to ethanol gas. Scanning electron microscopy revealed that the synthesized NiO nanoparticles were plate-shaped with the approximate size and thickness of 60 - 120 nm and 20 nm, respectively. On the other hand, $Co_3O_4$ nanoparticles mixed with NiO was observed to be spherical with the size range of 30 - 50 nm. The sensitivities of NiO sensors composited with $Co_3O_4$ nanoparticles at an optimal ratio of 8 : 2 were enhanced to approximately 1.44 - 1.79 times as high as those of as-synthesized NiO sensors for the ethanol concentration of 10 - 200 ppm at $200^{\circ}C$. The mechanism of the improved ethanol gas sensing of the NiO sensors composited with $Co_3O_4$ nanoparticles was discussed.

• 한국표면공학회지
• /
• 제52권5호
• /
• pp.258-264
• /
• 2019

Assembling heterostructures by combining dissimilar oxide semiconductors is a promising approach to enhance charge separation and transfer in photoelectrochemical (PEC) water splitting. In this work, the CuO nanorods array/$Cu_2O$ thin film bilayered heterostructure was successfully fabricated by a facile method that involved a direct electrodeposition of the $Cu_2O$ thin film onto the vertically oriented CuO nanorods array to serve as the photoelectrode for the PEC water oxidation. The resulting copper-oxide-based heterostructure photoelectrode exhibited an enhanced PEC performance compared to common copper-oxide-based photoelectrodes, indicating good charge separation and transfer efficiency due to the band structure realignment at the interface. The photocurrent density and the optimal photocurrent conversion efficiency obtained on the CuO nanorods/$Cu_2O$ thin film heterostructure were $0.59mA/cm^2$ and 1.10% at 1.06 V vs. RHE, respectively. These results provide a promising route to fabricating earth-abundant copper-oxide-based photoelectrode for visible-light-driven hydrogen generation using a facile, low-cost, and scalable approach of combining electrodeposition and hydrothermal synthesis.

• Nano
• /
• 제13권12호
• /
• pp.1850142.1-1850142.9
• /
• 2018

Modified titanate nanotubes (TNT) were tested for their adsorption of methylene blue (MB) from water solutions. They were obtained from the $TiO_2$ nanopowder using a standard alkaline hydrothermal method but in the stage of acid washing, when the titanate flakes begin to roll into nanotubes, magnetite nanoparticles were added. The $Fe_3O_4$ magnetic nanoparticles with diameter of around 2 nm and 12 nm were used in the tests. Significantly stronger adsorption of MB was observed when smaller nanoparticles were used compared to using larger nanoparticles and compared to the case of unmodified nanotubes. It was shown that the increased adsorption of MB is associated with a more negative value of ${\zeta}$-potential for titanates modified by the ultra-small nanoparticles. In the adsorption experiment, pH 7 was selected. These results may prove to be of great importance in the case of potential applications corresponding to the use of such material for wastewater purification.

• Nano
• /
• 제13권11호
• /
• pp.1850136.1-1850136.12
• /
• 2018

Three-dimensional (3D) mixed phases NiSe nanoparticles growing on the nickel foam were synthesized via a simple one-step hydrothermal method. A series of experiments were carried out to control the morphology by adjusting the amount of selenium in the synthetic reaction. Meanwhile, the as-prepared novel column-acicular structure NiSe exist three advantages including ideal electrical conductivity, high specific capacity and high cycling stability. It delivered a high capacitance of $10.8F\;cm^{-2}$ at a current density- of $5mA\;cm^{-2}$. An electrochemical capacitor device operating at 1.6 V was then constructed using NiSe/NF and activated carbon (AC) as positive and negative electrodes. Moreover, the device showed high energy density of $31W\;h\;kg^{-1}$ at a power density of $0.81kW\;kg^{-1}$, as well as good cycling stability (77% retention after 1500 cycles).

• Journal of Electrochemical Science and Technology
• /
• 제10권1호
• /
• pp.89-97
• /
• 2019

As a promising candidate for anode materials in lithium ion battery (LIB), tungsten trioxide ($WO_3$) and tungsten disulfide ($WS_2$) nanocrystals were synthesized, and their electrochemical properties were comprehensibly studied using a half cell. One-dimensional $WO_3$ nanowires with uniform diameter of 10 nm were synthesized by hydrothermal method, and two-dimensional (2D) $WS_2$ nanosheets by unique gas phase sulfurization of $WO_3$ using $H_2S$. $WS_2$ nanosheets exhibits uniformly 10 nm thickness. The $WO_3$ nanowires and $WS_2$ nanosheets showed maximum capacities of 552 and $633mA\;h\;g^{-1}$, respectively, after 100 cycles. Especially, the capacity of $WS_2$ is significantly larger than the theoretical capacity ($433mA\;h\;g^{-1}$). We also examined the cycling performance using a larger size $WO_3$ and $WS_2$ nanocrystals, showing that the smaller size plays an important role in enhancing the capacity of LIBs. The larger capacity of $WS_2$ nanosheets than the theoretical value is ascribed to the lower charge transfer resistance of 2D nanostructures.