대기압의 공기 분위기에서 열증발법에 의해 합성된 가지상 구조의 MgO 나노선

이근형 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.6

MgO nanowires with a branched structure were fabricated using a thermal evaporation methodin air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary centralnanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-foldsymmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of thecentral nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and werevertically well aligned in the same direction with each other. The scanning electron microscopy images of thebranched nanowires grown at 1000oC showed that the diameter of branches gradually decreased along thegrowth direction and no catalyst particle was found at the tips of the branches, indicating that the brancheswere grown by a vapor-solid process. For the branched nanowires grown at 1150oC, spherical particles whichwere shown to be catalysts were observed at the tips of the branches. The chemical analysis by energydispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. Theseresults suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. Thestructural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubiclattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowiresexhibited a very strong visible emission which was associated with oxygen vacancies.

Enhancement of gas sensing properties by the functionalization of ZnO-branched SnO₂ nanowires with Cr₂O₃ nanoparticles

Kwon, Yong Jung,Kang, Sung Yong,Mirzaei, Ali,Choi, Myung Sik,Bang, Jae Hoon,Kim, Sang Sub,Kim, Hyoun Woo Elsevier 2017 Sensors and actuators. B, Chemical Vol.249 No.-

<P><B>Abstract</B></P> <P>Complex metal oxides such as functionalized branched nanowires (NWs) are a new category of nanocomposites with unique properties for gas sensing applications. In the present work, we studied the gas sensing properties of Cr<SUB>2</SUB>O<SUB>3</SUB>-functionalized ZnO-branched SnO<SUB>2</SUB> NWs, inspired by their high surface area and numerous resistive points. These NWs were studied and compared with pristine SnO<SUB>2</SUB> NWs and ZnO-branched SnO<SUB>2</SUB> NWs. To prepare the functionalized NWs, ZnO-branched SnO<SUB>2</SUB> NWs were sputter-coated with a Cr layer and then annealed at 500°C to produce isolated Cr<SUB>2</SUB>O<SUB>3</SUB> NPs on the ZnO branches. Results of X-ray diffraction, scanning electron microscopy, and lattice-resolved transmission electron microscopy collectively showed that Cr<SUB>2</SUB>O<SUB>3</SUB>-functionalized ZnO-branched SnO<SUB>2</SUB> NWs were successfully formed. Cr<SUB>2</SUB>O<SUB>3</SUB> functionalization was found to greatly improve the sensors’ response to NO<SUB>2</SUB> gas. Furthermore, the sensors’ good selectivity was demonstrated by testing them in the presence of various interfering gases. The underlying gas sensing mechanisms are discussed herein in detail. We believe that the Cr<SUB>2</SUB>O<SUB>3</SUB>-functionalized ZnO-branched SnO<SUB>2</SUB> NWs reported herein are promising sensors for the highly sensitive and selective detection of NO<SUB>2</SUB> gas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cr<SUB>2</SUB>O<SUB>3</SUB>-functionalized ZnO-branched SnO<SUB>2</SUB> nanowires were successfully prepared. </LI> <LI> Cr<SUB>2</SUB>O<SUB>3</SUB> functionalization was found to greatly improve the sensors’ response to NO<SUB>2</SUB> gas. </LI> <LI> Underlying gas sensing mechanisms are discussed in terms of the Cr<SUB>2</SUB>O<SUB>3</SUB> spillover effect, the formation of Cr<SUB>2</SUB>O<SUB>3</SUB>/ZnO heterojunctions, and the creation of defects. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Selective NO₂ sensor based on Bi₂O₃ branched SnO₂ nanowires

Bang, Jae Hoon,Choi, Myung Sik,Mirzaei, Ali,Kwon, Yong Jung,Kim, Sang Sub,Kim, Tae Whan,Kim, Hyoun Woo Elsevier 2018 Sensors and actuators. B Chemical Vol.274 No.-

<P><B>Abstract</B></P> <P>We present a highly sensitive and selective NO<SUB>2</SUB> sensor based on Bi<SUB>2</SUB>O<SUB>3</SUB> branched SnO<SUB>2</SUB> nanowires (NWs). SnO<SUB>2</SUB> NWs were first synthesized by a vapor-liquid-solid method, were coated with an Au layer, and Bi<SUB>2</SUB>O<SUB>3</SUB> branches were grown on their stems by the same procedure used for pure Bi powders. The fabricated sensor showed a high response (R<SUB>g</SUB>/R<SUB>a</SUB>) of 56.92 to 2 ppm of NO<SUB>2</SUB> gas at an optimal temperature. Furthermore, its response to other interfering gases such as ethanol, acetone, toluene, and benzene, was less than 1.55, which demonstrated excellent selectivity of the sensor towards NO<SUB>2</SUB> gas. For comparison and to better understand the sensing mechanism, a pristine SnO<SUB>2</SUB> NWs sensor was also tested. The superior sensing properties of the branched NW sensor relative to the pristine sensor were mainly attributed to the high surface area of the sensor resulting from Bi<SUB>2</SUB>O<SUB>3</SUB> branching, as well as the formation of homo-and heterojunctions (Bi<SUB>2</SUB>O<SUB>3</SUB>-SnO<SUB>2</SUB>). In addition, several factors including the presence of Au contributed to the excellent selectivity to NO<SUB>2</SUB> gas. Based on the results obtained in this work, we believe that the present sensor with an easy fabrication method, along with its high sensitivity and selectivity towards NO<SUB>2</SUB>, can be used for the detection of NO<SUB>2</SUB> gas in real applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We presented a highly sensitive and selective NO<SUB>2</SUB> sensor based on Bi<SUB>2</SUB>O<SUB>3</SUB> branched SnO<SUB>2</SUB> nanowires. </LI> <LI> The sensor showed a high response (R<SUB>g</SUB>/R<SUB>a</SUB>) of 56.92 to 2 ppm of NO<SUB>2</SUB> gas </LI> <LI> The sensor demonstrated excellent selectivity towards NO<SUB>2</SUB> gas. </LI> <LI> We explored the sensing mechanisms, in regard to the selective sensing to NO<SUB>2</SUB> gas. </LI> </UL> </P>

Enhanced near-UV emission from self-catalytic brush-like GaN nanowires

Kim, S.,Park, S.,Ko, H.,Jeong, B.Y.,Lee, C. North-Holland 2014 Materials letters Vol.116 No.-

Recently, the enhanced field emission, photocatalytic activity and blue shift in UV emission of branched GaN nanowire structures were reported. Nevertheless, enhanced luminescence in branched GaN nanowires have not been reported despite the importance of short-wavelength emission. This paper reports synthesis of self-catalytic brush-like GaN nanowires exhibiting enhanced near-ultraviolet (NUV) emission. The diameters of the branches in the brush-like nanowires ranged from 3 to 14nm, whereas those of backbones ranged from 30 to 80nm. In contrast, the diameters of pristine nanowires were in a similar range to those of the backbones in the brush-like nanowires. The brush-like GaN nanowires showed significantly enhanced NUV emission compared to pristine GaN nanowires. This enhanced NUV emission might be due to the quantum confinement of excitons caused by the branches in the brush-like nanowires with diameters smaller than the Bohr exciton radius.

Nanoforest of Hydrothermally Grown Hierarchical ZnO Nanowires for a High Efficiency Dye-Sensitized Solar Cell

Ko, Seung Hwan,Lee, Daeho,Kang, Hyun Wook,Nam, Koo Hyun,Yeo, Joon Yeob,Hong, Suk Joon,Grigoropoulos, Costas P.,Sung, Hyung Jin American Chemical Society 2011 Nano letters Vol.11 No.2

<P>In this paper, in order to increase the power conversion efficiency we demonstrated the selective growth of “nanoforest” composed of high density, long branched “treelike” multigeneration hierarchical ZnO nanowire photoanodes. The overall light-conversion efficiency of the branched ZnO nanowire DSSCs was almost 5 times higher than the efficiency of DSSCs constructed by upstanding ZnO nanowires. The efficiency increase is due to greatly enhanced surface area for higher dye loading and light harvesting, and also due to reduced charge recombination by providing direct conduction pathways along the crystalline ZnO “nanotree” multi generation branches. We performed a parametric study to determine optimum hierarchical ZnO nanowire photoanodes through the combination of both length-wise growth and branched growth processes. The novel selective hierarchical growth approach represents a low cost, all solution processed hydrothermal method that yields complex hierarchical ZnO nanowire photoanodes by utilizing a simple engineering of seed particles and capping polymer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-2/nl1037962/production/images/medium/nl-2010-037962_0002.gif'></P>

Enhanced Photoluminescence of ZnSe Nanowires with Branches

이종무,박성훈,Jina Jun 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2

ZnSe nanowires have been grown by thermal evaporation of ZnSe powder on Si(100) and Al2O3(0001) substrates coated with gold (Au) thin films. ZnSe nanowires grown on Si(100) were thicker (~2 μm in diameter) and have numerous fine branch nanowires (20 50 nm in diameter and 400 – 500 nm in length) while those grown on Al2O3 (0001) were thinner (0.1 – 0.2 μm in diameter) and do not have branch nanowires. The former (ZnSe nanowires with branches) shows far stronger deep level photoluminescence (PL) emission than the latter. This enhanced PL emission may be attributed to the abundant surface states at the surfaces of the extremely fine branch nanowires which have a high surface-to-volume ratio.

Tailoring n-ZnO/p-Si Branched Nanowire Heterostructures for Selective Photoelectrochemical Water Oxidation or Reduction

Kargar, Alireza,Sun, Ke,Jing, Yi,Choi, Chulmin,Jeong, Huisu,Zhou, Yuchun,Madsen, Kristian,Naughton, Perry,Jin, Sungho,Jung, Gun Young,Wang, Deli American Chemical Society 2013 Nano letters Vol.13 No.7

<P>We report the fabrication of three-dimensional (3D) branched nanowire (NW) heterostructures, consisting of periodically ordered vertical Si NW trunks and ZnO NW branches, and their application for solar water splitting. The branched NW photoelectrodes show orders of magnitudes higher photocurrent compared to the bare Si NW electrodes. More interestingly, selective photoelectrochemical cathodic or anodic behavior resulting in either solar water oxidation or reduction was achieved by tuning the doping concentration of the p-type Si NW core. Specifically, n-ZnO/p-Si branched NW array electrodes with lightly doped core show broadband absorption from UV to near IR region and photocathodic water reduction, while n-ZnO/p<SUP>+</SUP>-Si branched NW arrays show photoanodic water oxidation with photoresponse only to UV light. The photoelectrochemical stability for over 24 h under constant light illumination and fixed biasing potential was achieved by coating the branched NW array with thin layers of TiO<SUB>2</SUB> and Pt. These studies not only reveal the promise of 3D branched NW photoelectrodes for high efficiency solar energy harvesting and conversion to clean chemical fuels, but also developing understanding enabling rational design of high efficiency robust photocathodes and photoanodes from low-cost and earth-abundant materials allowing practical applications in clean renewable energy.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-7/nl304539x/production/images/medium/nl-2012-04539x_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl304539x'>ACS Electronic Supporting Info</A></P>

3D Branched Nanowire Photoelectrochemical Electrodes for Efficient Solar Water Splitting

Kargar, Alireza,Sun, Ke,Jing, Yi,Choi, Chulmin,Jeong, Huisu,Jung, Gun Young,Jin, Sungho,Wang, Deli American Chemical Society 2013 ACS NANO Vol.7 No.10

<P>We report the systematic study of 3D ZnO/Si branched nanowire (b-NW) photoelectrodes and their application in solar water splitting. We focus our study on the correlation between the electrode design and structures (including Si NW doping, dimension of the trunk Si and branch ZnO NWs, and b-NW pitch size) and their photoelectrochemical (PEC) performances (efficiency and stability) under neutral conditions. Specifically, we show that for b-NW electrodes with lightly doped p-Si NW core, larger ZnO NW branches and longer Si NW cores give a higher <I>photocathodic</I> current, while for b-NWs with heavily doped p-Si NW trunks smaller ZnO NWs and shorter Si NWs provide a higher <I>photoanodic</I> current. Interestingly, the photocurrent turn-on potential decreases with longer p-Si NW trunks and larger ZnO NW branches resulting in a significant photocathodic turn-on potential shift of ∼600 mV for the optimized ZnO/p-Si b-NWs compared to that of the bare p-Si NWs. A photocathode energy conversion efficiency of greater than 2% at −1 V <I>versus</I> Pt counter electrode and in neutral solution is achieved for the optimized ZnO/p-Si b-NW electrodes. The PEC performances or incident photon-to-current efficiency are further improved using Si NW cores with smaller pitch size. The photoelectrode stability is dramatically improved by coating a thin TiO<SUB>2</SUB> protection layer using atomic-layer deposition method. These results provide very useful guidelines in designing photoelectrodes for selective solar water oxidation/reduction and overall spontaneous solar fuel generation using low cost earth-abundant materials for practical clean solar fuel production.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-10/nn404170y/production/images/medium/nn-2013-04170y_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn404170y'>ACS Electronic Supporting Info</A></P>

Branched ZnO-nanorod electrode for DSSCs

이정훈(Lee, Jung-Hoon),신유주(Shin, Yu-Ju) 한국신재생에너지학회 2007 한국신재생에너지학회 학술대회논문집 Vol.2007 No.06

Fabrication of branched Ga2O3 nanowires by post annealing with Au seeds

이미선,서창수,강현철 한국진공학회 2015 한국진공학회 학술발표회초록집 Vol.2015 No.8