수소 플라즈마 처리된 산화 아연 나노선의 자외선 발광 특성향상

강우승,박성훈,Kang, Wooseung,Park, Sunghoon 한국진공학회 2013 Applied Science and Convergence Technology Vol.22 No.6

ZnO nanowires were synthesized by vapor-liquid-solid (VLS) process using ZnO and graphite powders on the sapphire substrate coated with an Au film as a catalyst. ZnO nanowires had two prominent emission bands; i) near-band edge (NBE) emission band at 380 nm, and ii) a relatively stronger deep level (DL) emission band ($I_{NBE}/I_{DL}$ <1). In order for the ZnO nanowires to be utilized as an effective material for UV emitting devices, the photoluminescence intensity of NBE needs to be improved with the decreased intensity of DL. In the current study, hydrogen plasma treatment was performed to improve the photoluminescence characteristics of ZnO nanowires. With the hydrogen plasma treatment time of more than 120 sec, the extent of performance improvement was gradually decreased. However, the intensity ratio of NBE to DL ($I_{NBE}/I_{DL}$) was significantly improved to about 4 with a relatively short plasma treatment time of 90 sec, suggesting hydrogen plasma treatment is a promising approach to improve the photoluminescence properties of ZnO nanowires. Au 촉매를 코팅한 사파이어 기판 상에서 산화아연과 흑연 분말을 혼합한 분말재료를 이용하여 VLS (vapor-liquid-solid) 법으로 산화아연 반도체 나노선을 합성하였다. 제조된 산화아연 나노선은 380 nm에서 근 자외선 영역의 NBE (near-band edge) 발광과 600 nm 부근의 가시광선 영역에서 넓게 퍼져 발광하는 상대적으로 강한 DL (deep level) 발광이 확인되었다($I_{NBE}/I_{DL}$ <1). 산화아연 나노선을 효율적인 단일 파장 자외선 발광체에 적용될 수 있도록 NBE 발광을 극대화함과 동시에 DL 발광을 억제시키기 위하여 본 실험에서는 합성된 산화아연 나노선에 수소 플라즈마 처리를 하였다. 플라즈마 처리시간이 길어짐에 따라(120초 이상) 발광특성의 향상정도는 점차로 감소하였지만, 수소 플라즈마 처리를 통해 나노선 내부에 존재하는 불순물 제어 등으로 다소 짧은 시간의 플라즈마 처리로(90초 이내) DL발광대비 NBE발광의 세기가 약 4배로 향상됨을 확인 하였다($I_{NBE}/I_{DL}$ ~4).

산화코발트 나노입자의 첨가에 따른 산화니켈 기반 반도체 산화물의 에탄올 가스 검출 특성 향상

강우승(Wooseung Kang) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.4

NiO nanoparticles were synthesized by hydrothermal method for the application to ethanol gas sensor. They were composited with Co₃O₄ 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, Co₃O₄ nanoparticles mixed with NiO was observed to be spherical with the size range of 30 - 50 nm. The sensitivities of NiO sensors composited with Co₃O₄ 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℃. The mechanism of the improved ethanol gas sensing of the NiO sensors composited with Co₃O₄ nanoparticles was discussed.

산화아연 나노튜브의 벽 두께에 따른 에탄올 가스 검출특성

강우승(Wooseung Kang) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.3

ZnO nanotubes were synthesized to investigate the effect of wall thickness on the ethanol gas sensing performance. The wall thickness of the nanotubes was varied from approximately 20 to 60 nm. Transmission electron microscopy, X-ray diffraction and SAED (Selected Area Electron Beam Diffraction) analyses showed that the synthesized nanotubes were polycrystalline structured ZnO with the diameter of approximately 200-300nm. The ZnO nanotubes sensor with an optimum wall thickness of 51.8nm showed approximately 8 times higher response, compared to that with 21.14nm wall thick nanotubes, to the ethanol concentration of 500 ppm at the temperature of 300℃. The wall thickness of 51.8nm was found to be a little larger than 46nm, which was theoretically derived Debye length. Along with the study of the wall thickness effect on the performance of the sensors, the mechanisms of gas sensing of the polycrystalline ZnO nanotubes are also discussed.

산소 분위기 열처리에 따른 ZnO 나노선의 상온 영역에서의 수소가스 검출 특성 향상

강우승(Wooseung Kang) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.2

ZnO nanowires were synthesized and annealed at various temperatures of 500-800℃ in oxygen atmosphere to investigate hydrogen gas sensing properties. The diameter and length of the synthesized ZnO nanowires were approximately 50-100 nm and a few 10s μm, respectively. H₂ gas sensing performance of the ZnO nanowires sensor was measured with electrical resistance changes caused by H₂ gas with a concentration of 0.1-2.0%. The response of ZnO nanowires at room temperature to 2.0% H₂ gas is found to be two times enhanced by annealing process in O₂ atmosphere at 800℃. In the current study, the effect of heat treatment in O₂ atmosphere on the gas sensing performance of ZnO nanowires was studied. And the underlying mechanism for the sensing improvement of the ZnO nanowires was also discussed.

Au 촉매금속이 첨가된 NiO 나노섬유의 가스 검출 특성

강우승(Wooseung Kang) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.4

NiO nanofibers with Au nanoparticles were synthesized by sol-gel and electrospinning techniques, in which the reduction process by ultraviolet exposure is included for the growth of Au nanoparticles in the electrospinning solution. FE-SEM(Field Emission Scanning Electron Microscopy), TEM(Transmission Electron Microscopy) revealed that the synthesized nanofibers had the diameter of approximately 200 nm. X-ray diffraction showed the successful formation of Au-decorated NiO nanofibers. Gas sensing tests of Au-decorated NiO nanofibers were performed using reducing gases of CO, and C6H6, C7H8, C₂H5OH. Compared to assynthesized NiO nanofibers, the response of Au-loaded NiO nanofibers to CO gas was found to be about 3.4 times increased. On the other hand, the response increases were only 1.1-1.3 times for C6H6, C7H8, and C₂H5OH.

Au 나노입자가 코팅된 TiO₂ 나노와이어의 에탄올가스 검출 특성

강우승(Wooseung Kang) 한국표면공학회 2015 한국표면공학회지 Vol.48 No.5

TiO₂ nanowires were synthesized by hydrothermal method for the application to ethanol gas sensor. TiO₂ 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 TiO₂ 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-TiO₂, and Au. The sensitivities of TiO₂ nanowires sensors decorated with Au were approximately 1.1 - 3.65 times as high as those of as-synthesized TiO₂ sensors for the ethanol concentration of 5 - 100 ppm at 200℃. The mechanism of the improved ethanol gas sensing of the TiO₂ nanowires decorated with Au nanoparticles is discussed.

상온에서 UV 활성화된 ZnS 나노와이어의 NO₂ 가스 검출 특성

강우승(Wooseung Kang) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.6

ZnS nanowires were synthesized in order to investigate NO₂ gas sensing properties. They were grown on the sapphire substrate using ZnS powders. SEM (scanning electron microscopy) showed the diameter and length of the ZnS nanowires were approximately in the range of 50 - 100 nm and a few 10s μm, respectively. They were also found to be composed of Wurtzite- structured single crystals from TEM (transmission electron microscopy) analysis. NO₂ gas sensing performance of the ZnS nanowire was measured with electrical resistance changes caused by NO₂ gas with a concentration of 1-5ppm. The sensor was UV treated with an intensity of 1.2 mW/cm2 to facilitate charge carrier transfer. The responses of the ZnS nanowires to the NO₂ gas at room temperature, treated with UV of two different wavelengths of 365 nm and 254 nm, are measured to be 124.53 - 206.87 % and 233.97 - 554.83%, respectively. In the current work, the effect of UV treatment on the gas sensing performance of the ZnS nanowires was studied. And the underlying mechanism for the electrical resistance changes of the ZnS nanowires by NO₂ gas was also discussed.

Pd 나노입자가 코팅된 β-Bi₂O₃ 나노와이어의 NO₂ 검출 특성

박성훈(Sunghoon Park),강우승(Wooseung Kang) 한국표면공학회 2015 한국표면공학회지 Vol.48 No.6

Pd-functionalized β-Bi₂O₃ nanowires are synthesized by thermal evaporation of Bi powder using VLS mechanism followed by Pd coating and annealing. In this study, sensing properties of Pd-functionalized β-Bi₂O₃ nanowires sensor to selected concentrations of NO₂ gas were examined. Scanning electron microscopy showed that the nanowires with diameters in a range of 100 - 200 nm and lengths of up to a few tens of micrometers. Transmission electron microscopy and X-ray diffraction confirmed that the products corresponded to the nanowires of β-Bi₂O₃ crystals and Pd nanoparticles. Pd-functionalized β-Bi₂O₃ nanowires sensor showed an enhanced sensing performance to NO₂ gas compared to as-synthesized β-Bi₂O₃ nanowires sensor. As synthesized and Pd-functionalized β-Bi₂O₃ nanowire sensors showed responses of 178% - 338% and 196% - 535% at 300℃, respectively, to 0.05 - 2 ppm NO₂. In addition, the underlying mechanism of the enhancement of the sensing properties of β-Bi₂O₃ nanowires by Pd-functionalization is discussed.

NiO의 첨가에 따른 α-Fe₂O₃ 나노입자 센서의 에탄올 가스 검출 특성 향상

박성훈(Sunghoon Park),강우승(Wooseung Kang) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.1

In order to investigate the effect of NiO on the ethanol gas sensing performance of α-Fe₂O₃ nanoparticles, NiO and α-Fe₂O₃ nanoparticles are synthesized by hydrothermal method. The sensor with α-Fe₂O₃ and NiO nanoparticles mixed at an optimum ratio of 7:3 showed 3.8 times improved sensing performance for 200ppm ethanol gas at 200°C. The enhanced gas sensing performance can be considered to be caused by pn heterojunction at the grain boundaries of α-Fe₂O₃ and NiO nanopartcles.

Co₃O₄ 나노입자가 코팅된 In₂O₃ 나노와이어의 에탄올 가스 검출 특성

박성훈(Sunghoon Park),강우승(Wooseung Kang) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.1

In₂O₃ nanowires were coated with Co₃O₄ nanoparticles to investigate the improvement of ethanol gas sensing performance compared with as-synthesized In₂O₃ 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. Co₃O₄ nanoparticles produced by hydrothermal method was in the size range of a few to a few tens nm. As-synthesized and Co₃O₄ nanoparticles coated In₂O₃ nanowires sensors exhibited responses of 1.96% and 4.57%, respectively for the ethanol gas concentration of 200 ppm at 200°C. The underlying mechanism for the improved responses of Co₃O₄ nanoparticles coated In₂O₃ nanowires sensors is discussed.