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김소아람,김민수,임광국,임재영,남기웅,이동율,김진수,김종수,손정식 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10
Zinc oxide (ZnO) submicron particles were synthesized on Au-catalyzed Si substrate by using vapor phase transport (VPT), using a mixture of zinc oxide and graphite powders as source material at atmospheric pressure. Au catalyst layers with the thickness of 75.6 Å were deposited by using thermal evaporator. ZnO submicron particles were synthesized under various growth conditions, such as growth temperature ranging from 700 to 1000 ℃ and distance between the source material and substrate ranging from 5 to 50 mm, in argon carrier and oxygen reaction gas ambient. The structural and optical properties of the ZnO submicron particles were investigated by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL). From the SEM images of the first experimental series, which are grown at various growth temperatures, dispersively distributed submicron particles with diameters ranging from 100 to 500 nm were formed on the substrates. The largest average diameter of the ZnO submicron particles was obtained at the growth temperature of 800 ℃. In addition, the highest intensity and narrowest full width at half maximum (FWHM) of the ZnO (002) diffraction peak located at 34.4˚ were observed from the ZnO submicron particles grown at 800 ℃. In the PL spectra, the intensity of the near-band-edge emission (NBE) peak was rapidly increased with increasing the growth temperature to 800 ℃, and then decreased with increasing the growth temperature up to 1000 ℃. In the second experimental series with various distance between the powder source and Si substrate, the ZnO submicron particles exhibited the different grain size in the range of 100 to 250 nm. As the distance from the source increased, the grain size of the ZnO submicron particles increased because more O<SUB>2</SUB> molecules remained in the small quartz tube. The ZnO (002) diffraction peak located at 34.4˚ was the most intensive among ZnO diffraction peaks. And also, the FWHM of the ZnO (002) diffraction peak was 0.062˚ with distance of 50 mm. In the PL spectra, except for the sample with distance of 5 mm, other samples showed dominant NBE peak located at about 3.28 eV.
김소아람,남기웅,Kwang Gug Yim,이제원,김양수,임재영 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.3
ZnO nanostructures were grown by the hydrothermal method on ZnO seed layers post-heated in the range 350°C - 500°C. The effects of the post-heated ZnO seed layers on the structural and optical properties of the ZnO nanostructures were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD)spectroscopy, and photoluminescence (PL) spectroscopy. The average grain sizes in the ZnO seed layers increased with increasing post-heating temperature, and nano-fibrous structures were observed on the surface of the ZnO seed layers post-heated at 450°C. The ZnO seed layers post-heated in the range 350°C - 500°C affected the residual stress, lattice distortion in the ZnO nanostructures and the intensity, positions, and full widths at half maximum of 2θ and PL peaks in the XRD and PL spectra for the ZnO nanostructures.
Temperature-dependent Photoluminescence of Boron-doped ZnO Nanorods
김소아람,박형길,남기웅,Hyunsik Yoon,김종수,Jinsoo Kim,Jeong-Sik Son,이상헌,임재영 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons (DoX), and the first LO phonon replicas of DoX, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni’s empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.
김소아람,남기웅,박형길,윤현식,이상헌,김종수,김진수,Do Yeob Kim,김성오,임재영 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
The structural and optical properties of the ZnO, Al-doped ZnO, Ga-doped ZnO, and In-doped ZnO nanorods were investigated using field-emission scanning electron microscopy, X-ray diffraction, photoluminescence (PL) and ultraviolet-visible spectroscopy. All the nanorods grew with good alignment on the ZnO seed layers and the ZnO nanorod dimensions could be controlled by the addition of the various dopants. For instance, the diameter of the nanorods decreased with increasing atomic number of the dopants. The ratio between the nearband- edge emission (NBE) and the deep-level emission (DLE) intensities (INBE/IDLE) obtained by PL gradually decreased because the DLE intensity from the nanorods gradually increased with increase in the atomic number of the dopants. We found that the dopants affected the structural and optical properties of the ZnO nanorods including their dimensions, lattice constants, residual stresses, bond lengths, PL properties, transmittance values, optical band gaps, and Urbach energies.
김소아람,박형길,남기웅,윤현식,김병규,지익수,김영규,김익현,박영빈,Daeho Kang,임재영 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.1
The structural, optical, and electrical properties of ZnO and BZO nanorods were investigated using fieldemission scanning electron microscopy, x-ray diffraction (XRD), photoluminescence (PL), and van der Pauw Hall-effect measurements. All the nanorods had grown well on the ZnO seed layers and were hexagonal. The BZO nanorods were shorter than the undoped ZnO nanorods, and the BZO nanorods grew shorter with increasing concentration of B to 2.0 at. % while the average length of the nanorods doped with 2.5 at. % B increased from 1620 to 1830 nm. The XRD patterns suggest that the amount of residual stress in the nanorods decreased with increasing concentration of B in the nanorods. The PL spectra showed near-bandedge and deep-level emissions, and B doping also varied the PL properties of the ZnO nanorods. The Halleffect data suggest that B doping also varied the electrical properties such as the carrier concentration, mobility, and resistivity of the ZnO nanorods.
김소아람,남기웅,임재영 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.5
ZnO submicron particles were grown on Au-catalyzed Si substrates using a vapor phase transport (VPT) growth process under different mixture gas ratios at a growth temperature of 900°C. The structural and optical properties of the ZnO submicron particles were investigated using field-emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), and photoluminescence (PL). The ZnO submicron particles were clustered for the O2/ Ar mixture gas ratios (%) higher than 10%, which was largely determined by the ambient gas. In particular, for an O2/Ar mixture gas ratios of 30%, ZnO submicron particles with diameters between 125 - 500 nm were observed; in addition, the narrowest XRD full width at half maximum (FWHM) values and PL spectra with 0.121° and 92 meV were reported. The structural and optical properties of the ZnO submicron particles improved as the O2/Ar mixture gas ratio was increased, as observed from the XRD and PL spectra results.