http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Au-assisted growth, Raman spectra, and photoluminescence of Mg2SiO4 nanowires
나한길,Tran Van Khai,곽동섭,권용중,심광보,김성수,정현식,김현우 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.3
We have prepared Mg2SiO4 nanowires by a thermal heating method with Au-coated substrates gathering the products. We investigated the effect of the Au layer thickness on the nanowire morphology using scanning electron microscopy, suggesting a possible growth mechanism of Mg2SiO4 nanowires. XRD spectra and lattice-resolved TEM images indicated that the nanowires had an orthorhombic Mg2SiO4 phase. For the first time, we report the Raman and photoluminescence (PL) spectra of Mg2SiO4 nanowires. Raman lines corresponding to the SiO4 group from Mg2SnO4 were observed. The PL measurement with a Gaussian fitting exhibited visible light emission bands centered at 2.03, 2.21, 2.45, and 2.95 eV.
나한길,곽동섭,권용중,Fan Xia,박원일,김현우 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2
We have investigated the effects of the oxygen gas flow ratio in a synthesis process, ultimately producing thin (~40 nm in diameter) SnO2 nanowires. Scanning electron microscopy revealed that the oxygen partial pressure affected the diameter as well as the length of the nanowires. An X-ray diffraction investigation suggested that the grain size of the SnO2 phase was slightly increased with a decrease in the oxygen partial pressure. Lattice-resolved transmission electron microscopy (TEM)images, selected area electron diffraction, and micro-Raman spectroscopy coincidentally showed that the as-synthesized nanowires comprised a tetragonal SnO2 phase. Based on the analysis by fabricating field effect transistors, we found that the transport properties of SnO2 nanowires exhibited an n-type semiconductor characteristic.
TiO2/SiOx Core-Shell Nanowires Generated by Heating the Multilayered Substrates
나한길,곽동섭,권용중,조홍연,이종무,김현우 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.4
By heating Au/TiN/Si substrates, we fabricated TiO2/SiOx core-shell nanowires. By changing the thickness of predeposited Au layers, we demonstrated that the thickness of the Au layer needs to be optimized to obtain nanowires. High-resolution transmission electron microscopy image, X-ray diffraction spectrum,and selected area electron diffraction pattern coincidentally revealed that the resultant core nanowires had a tetragonal rutile structure of TiO2, and the shell was comprised of amorphous SiOx. The dominant growth mechanism was a base-growth mode, in which Au played a catalytic role, resulting in morphological changes with variation of the Au layer thickness. The TiO2/SiOx core-shell nanowires exhibited a broad photoluminescence emission band, which comprised four peaks centered at 1.54, 2.34, 2.67, and 2.99 eV,respectively. We expected that the 1.54 eV- and 2.34 eV-centered peaks arised from the TiO2 core, whereas the 2.67 eV- and 2.34 eV-peaks were ascribed to both the TiO2 core and the SiOx shell.
Decoration of Ag nanoparticles on reduced graphene oxide and their application to gas sensors
나한길,권용중,강성용,강우승,최명식,방재훈,정택균,이종무,김현우 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.6
We fabricated functionalized RGO that demonstrates excellent sensitivity to H2S gas. The functionalization process used GOsuspensions mixed with AgNO3, NaOH, and DI water. X-ray diffraction (XRD) and transmission electron microscopyindicated that the functionalizing structures were composed of cubic Ag and silver oxide (AgxOy) phases. Nanoparticles andnanorods with a cubic Ag phase were attached to the surface of the RGO. Raman spectra revealed that the structural disorderof the functionalized RGO was higher than that of pristine GO. The decrease of resistance by the introduction of H2S gasindicated that the functionalized RGO was an n-type sensor. Accordingly, we suggested that the n-type AgxOy, whose presencewas confirmed by XRD, should be a main current path for the sensor. A H2S gas sensing test revealed that the sensor responseat 50 ppm was about 1.65. With respect to H2S sensing mechanisms, we propose that the following four reasons could explainthe significant enhanced sensitivity by the functionalization: (i) reduction of the conduction volume by the conduction throughthe AgxOy structure rather than RGO, (ii) generation of silver sulfide structures, (iii) generation of an n-AgxOy/p-RGOheterointerface, and (iv) larger surface area of Ag/AgxOy structures. The Ag catalyst is not only the source of the AgxOy, butalso provides the spillover effect.
Synthesis and Room-Temperature NO2 Sensing Properties of Sb2O5 Nanowires
김상섭,나한길,권용정,조홍연,김현우 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.2
The sensing properties of Sb2O5 nanowires are reported for the first time. By varying the heating temperature ofa mixture of Sb and Bi powders, we have successfully prepared Sb2O5 nanowires. For nanowires grown at600°C, the stem is mainly comprised of a monoclinic Sb2O5 phase, with a trace amount of a monoclinicBi2O3 phase. The existence of Au nanoparticles at the tips suggests that the 600°C-synthesized nanowiresare mainly grown via a vapor-liquid-solid process. The 500°C-grown products comprise a small amount of1D nanostructures, whereas the 700°C-grown product does not exhibit sufficiently thin 1D nanostructures. A representative A survey XPS spectrum exhibits several peaks, including Sb 3p, Sb 3d, O 1s, C 1s, Bi 4f, andSb 4d. At room temeperature, the sensor response, response time, and recovery time of the nanowires weremeasured to be 1.20, 2104 s, and 6579 s, respectively. Sensor measurements employing NO2 gas indicate thatthe Sb2O5 nanowires synthesized in this work have potential for use as a room-temperature NO2 chemicalgas sensors.
Extended Energy Conservation Law in Alloys: the Absence of Energy Non-Equilibrium
최명식,나한길,진창현,이규형 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.8
Assuming that many of the materials produced in a non-equilibrium state remain unchanged, an extended space–energy conservation law was proposed based on the existing energy conservation law. In the present study, by analyzing the well developed equilibrium binary phase diagram of iron (Fe) – carbon (C), we show that energy non-equilibrium microstructures can appear as a part of the equilibrium between the space energy and the mass energy. The correlation between these two energies is objectively and logically explained via (1) one-to-one correspondences between the equilibrium and non-equilibrium phases based on the binary Fe–C phase diagram and (2) the heat-treated Fe–C phases with the spatial energy represented by temperature. Additionally, we found that the morphological and microstructural changes in non-equilibrium states could be consistently explained using the extended energy law as a major premise. This suggests that material factors such as size, distribution, and the shape of materials, which appear to have no energy transfer, are all formed to balance the energy equilibrium with the spatial energy surrounding the materials. Thus, an extended energy conservation law, which can control mass through space or vice versa, can provide a comprehensive logical framework for analyzing various unsolved physicochemical phenomena.
수열합성법을 이용한 세륨산화물 나노분말의 특성 및 합성에 대한 연구
공명호,나한길,김현우,양학희,Kong, Myung-Ho,Na, Han-Gil,Kim, Hyoun-Woo,Yang, Hack-Hui 한국반도체디스플레이기술학회 2010 반도체디스플레이기술학회지 Vol.9 No.2
We have successfully synthesized $CeO_2$ nanopowders by means of the hydrothermal method, in a low temperature range of $100-200^{\circ}C$. In order to investigate the structure and morphology of the nanopowders, scanning electron microscopy and X-ray diffraction have been employed. In addition, for exploring the optical properties, Raman spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy have been used. In the optimized condition, with the pH, velocity, and time of 4.5, 600 rpm, and 60 h, the $CeO_2$ nanopowders with a diameter ranging from 50 to 150 nm have been synthesized. The nanopowders exhibited the visible emission mainly in the blue region. With comparing the reaction time, it is revealed that the extinction of functional groups at 60 h contributed to the growth and homogenization of the $CeO_2$ powders. Since the overgrowth and agglomeration of nanopowders were found, we suggest that the cracking/growth process is more favorable mechanism than the dissolution/precipitation process.
Decoration of MgO nanowires with Gd2O3 nanoparticles: structure and photoluminescence properties
강우승,나한길,권용중,조홍연,강성용,박재영,이종무,공명호,김현우 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.4
We decorated coated Gd2O3 nanoparticles on MgO nanowires by means of Gd sputtering and subsequent thermal annealing. The samples were characterized by X-ray diffraction, scanning electron microscope (SEM), and transmission electron microscopy. The surface roughness observed by SEM was revealed to be Gd2O3 nanoparticles in terms of TEM observation. The PL spectra exhibited a 2.9 eV-peak, which originated from the MgO nanowires, and thermal annealing produced green emission at about 2.4 eV, which is directly associated with the Gd2O3 structure. An additional weak peak at 2.0 eV was found to be related to impurities in the Gd2O3 structure.
김현우,양주찬,나한길,곽동섭,이종무 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.4
This study addresses the annealing effects of ZnO/SiOx core-shell nanowire optical properties, in terms of Zn2SiO4 crystallite generation. At 700 °C, the integrated PL intensity of deep-level emission was increased by annealing. With regard to UV emission, free exciton (FX) peak intensity was reduced and the ratio of FX to non-FX peak intensities increased as annealing temperature was increased. These annealing induced changes, including the enhancement of deep-level emission and suppression of FX emission, are mainly related to the generation of Zn2SiO4 crystallites. Transmission electron microscopy revealed that Zn2SiO4crystallites were formed inside the SiOx shell layer.