• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.247-247
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• 2011

플라즈마 분자선 에피택시(plasma-assisted molecular beam epitaxy)법을 이용하여 다공질 실리콘(porous silicon)에 ZnO 박막을 성장하였다. 성장 후, 아르곤 분위기에서 10분 간 다양한 온도(500~700$^{\circ}C$)로 열처리하였다. 다공질 실리콘 및 열처리 온도가 ZnO 박막의 특성에 미치는 영향을 scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL)을 이용하여 분석하였다. 실리콘 기판에 성장된 ZnO 박막은 일반적은 섬구조(island structure)로 성장된 반면, 다공질 실리콘에 성장된 ZnO 박막은 산맥과 같은 구조(mountain range-like structure)로 성장되었다. 열처리 온도가 증가함에 따라 ZnO 박막의 grain size는 증가하였다. 실리콘 기판 위에 성장된 ZnO 박막은 wurtzite 구조를 나타내는 여러 개의 회절 피크가 관찰된 반면, 다공질 실리콘에 성장된 ZnO 박막은 c-축 배향성(c-axis preferred orientation)을 나타내는 ZnO (002) 회절 피크만이 나타났다. 다공질 실리콘에 성장된 ZnO 박막의 구조적 및 광학적 특성이 실리콘 기판에 성장된 ZnO 박막의 특성보다 우수하게 나타났다. 뿐만 아니라, 열처리 온도가 증가함에 따라 다공질 실리콘에 성장된 ZnO 박막의 PL 강도비(intensity ratio)가 실리콘 기판에 성장된 ZnO 박막의 강도비보다 월등하게 증가하였다.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1283-1285
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• 1997

In this paper, structural, optical and electrical properties of $Cd_{1-x}Zn_xS$ thin films prepared by co-evaporation method were studied. The crystal structure of $Cd_{1-x}Zn_xS$ films deposited at a substrate temperature of $150^{\circ}C$ was hexagonal with the c axis aligned perpendicular to the substrate. As increasing composition parameter x, the intensity of (002) peak decreased, which means poor crystalline and decreasing of preferential orientation. The optical bandgap of $Cd_{1-x}Zn_xS$ films varies from 2.41eV for CdS to 3.48eV for ZnS with x. The resistivity of the $Cd_{1-x}Zn_xS$ films increased with x.

• Nuclear Engineering and Technology
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• v.46 no.4
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• pp.513-520
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• 2014

In this paper, three types of operational and industrial absorbers used at research reactors, including Ag-In-Cd alloy, $B_4C$, and Hf are selected for sensitivity analyses. Their integral effects on the main neutronic core parameters important to safety issues are investigated. These parameters are core excess reactivity, shutdown margin, total reactivity worth of control rods, thermal neutron flux, power density distribution, and Power Peaking Factor (PPF). The IAEA 10 MW benchmark core is selected as the case study to verify calculations. A two-dimensional, three-group diffusion model is selected for core calculations. The well-known WIMS-D4 and CITATION reactor codes are used to carry out these calculations. It is found that the largest shutdown margin is gained using the $B_4C$; also the lowest PPF is gained using the Ag-In-Cd alloy. The maximum point power densities belong to the inside fuel regions surrounding the central flux trap (irradiation position), surrounded by control fuel elements, and the peripheral fuel elements beside the graphite reflectors. The greatest and least fluctuation of the point power densities are gained by using $B_4C$ and Ag-In-Cd alloy, respectively.

• Journal of the Semiconductor & Display Technology
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• v.15 no.4
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• pp.41-45
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• 2016

ITO/GZO double layered thin films were prepared on transparent glass substrates. Ga-doped ZnO(GZO) films were deposited by RF magnetron sputtering using an ZnO:Ga (98: 2 wt%) target. The post deposition annealing process was conducted for 30 minutes at different temperature of 100, 200, 300 and $400^{\circ}C$, respectively. As increase annealing temperature, ITO/GZO double layered thin films show the increment of the prefer orientation of ZnO diffraction peak (002) in the XRD patterns. We obtained Ga-doped ZnO thin films with a lowest resistivity of $1.84{\times}10^{-4}{\Omega}-cm$ at $400^{\circ}C$ and transparency above 80% in visible ranges. The figure of merit obtained in this study means that ITO/GZO double layered thin films which annealed at $400^{\circ}C$ have the highest optoelectrical performance in this study.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.880-884
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• 2011

ZnO nanorods were grown by hydrothermal method. Two kinds of seed layers, Au film and island seed layers were prepared to investigate the effect of seed layer on ZnO nanorods. The ZnO nanorod on Au island seed layer has more unifom diameter and higher density compared to that of ZnO nanorod on Au film seed layer. The ZnO nanorods on Au island seed layer were annealed at various temperatures ranging from 300 to $850^{\circ}C$. The pinholes at the surface of the ZnO nanorods is formed as the annealing temperature is increased. It is noted that the pyramid structure on the surface of ZnO nanorod is observed at $850^{\circ}C$. The intensity of ZnO (002) diffraction peak in X-ray diffraction pattern and intensity of near band edge emission (NBE) peak in photoluminescence (PL) are increased as the ZnO nanorods were annealed at the temperature of $300^{\circ}C$.

• Carbon letters
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• v.8 no.2
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• pp.95-100
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• 2007

A series of activated carbons (ACs) were derived from sugarcane bagasse under two activation schemes: steam-pyrolysis at $600-800^{\circ}C$ and chemical activation with $H_3PO_4$ at $500^{\circ}C$. Some carbons were treated at 400, $600^{\circ}C$, or for 1-3 h, and/or in flowing air during pyrolysis of acid-impregnated mass. XRD profiles displayed two broad diffuse bands centered around $2{\theta}=23$ and $43^{\circ}$, currently associated with diffraction from the 002 and 100/101 set of planes in graphite, respectively. These correspond to the interlayer spacing, Lc, and microcrystallite lateral dimensions, La, of the turbostratic (fully disordered) graphene layers. Steam pyrolysis-activated carbons exhibit only the two mentioned broad bands with enhancement in number of layers, with temperature, and small decrease in microcrystallite diameter, La. XRD patterns of $H_3PO_4$-ACs display more developed and separated peaks in the early region with maxima at $2{\theta}=23$, 26 and $29^{\circ}$, possibly ascribed to fragmented microcrystallites (or partially organized structures). Diffraction within the $2{\theta}=43^{\circ}$ is still broad although depressed and diffuse, suggesting that the intragraphitic layers are less developed. Varying the conditions of chemical activation inflicts insignificant structural alterations. Circulating air during pyrolysis leads to enhancement of the basic graphitic structure with destruction and degradation in the lateral dimensions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.417-418
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• 2008

Transparent conductive oxide (TCO) are necessary as front electrode or anti-reflecting coating for increasing efficiency of LED and Photodiode. In this paper, aluminum-doped Zinc oxide films(AZO) were prepared by DC magnetron sputtering on glass(corning 1737) and Si substrate at temperature of $100^{\circ}C$ and then annealed at temperature of $400^{\circ}C$ for 1hr in Ar and vaccum. The AZO films were etched in diluted HCL (0.5 %) to examine the surface morphology properties. After annealing, Structural and electrical property were investigated. The c-axis orientation along (002) plane was enhanced and the electrical resistivity of the AZO film decreased from $1.1\times10^{-1}$ to $1.6\times10^{-2}{\Omega}cm$. We observed textured structure of AZO thin film etched for 2s.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.185-188
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• 2009

The effects of the growth temperature on the properties of ZnO thin films were investigated by using X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectrophotometry, and Hall measurements. The ZnO films were deposited by rf magnetron sputtering at various growth temperatures in the range of 100-$400{^{\circ}C}$. A strong c-axis preferred orientation is observed for all of the samples. As the growth temperature increases, the crystalline orientation of the ZnO (002) plane is not changed, but the full width at half maximum gets smaller. The dependence of the electron concentration, mobility, and resistivity on the growth temperature exhibits that the ZnO films have a higher electron concentration at higher temperatures, thus giving them a low resistivity. The optical transmittance and band gap energy, calculated from the spectra of optical absorbance, show a significant dependence on the growth temperature. As for the sample grown at $100{^{\circ}C}$, the average transmittance is about 90% in the visible wavelength range and the band gap is estimated to be 3.13 eV.

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.88-89
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• 2007

ZnO thin films were deposited on $Al_2O_3$ (alumina) substrates by pulsed laser deposition (PLD) using Nd:YAG laser with a wavelength of 355nm, at room temperature and oxygen partial pressure of 1, 10, 30, 50, 100, and 200m Torr. Furthermore, deposited ZnO thin films were post-annealed at 400, 550, $600^{\circ}C$. The effects of oxygen partial pressure and post-annealing temperature on structural properties of the deposited films have been investigated by means of X-ray diffraction (XRD), and atomic force microscope (AFM), respectively. It has been found that ZnO thin films exhibit c-axis orientation, exhibiting an increased foil width at half maximum (FWHM) value of (002) diffraction peak at 30m Torr oxygen partial pressure and higher post-annealing temperature ($700^{\circ}C$).

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.390-390
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• 2010

Superconducting proximity effects of Nb/Si(111) were investigated with scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS). A highly-doped($0.002\;{\omega}{\diamondsuit}cm$) Si wafer pieces were used as substrate and Nb source was thermally evaporated onto the atomically clean silicon substrate. The temperature of the silicon sample was held at $600^{\circ}C$ during the niobium deposition. And the sample was annealed at $600^{\circ}C$ for 30 minutes additionally. Volmer-Weber growth mode is preferred in Nb/Si(111) at the sample temperature of $600^{\circ}C$. With proper temperature and annealing time, we can obtain Nb islands of lateral size larger than Nb coherence length(~38nm). And outside of the islands, bare Si($7{\times}7$) reconstructed surface is exposed due to the Volmer-Weber Growth mode. STS measurement at 5.6K showed that Nb island have BCS-like superconducting gap of about 2mV around the Fermi level and the critical temperature is calculated to be as low as 6.1K, which is lower than that of bulk niobium, 9.5K. This reduced value of superconducting energy gap indicates suppression of superconductivity in nanostructures. Moreover, the superconducting state is extended out of the Nb island, over to bare Si surface, due to the superconducting proximity effect. Spatially-resolved scanning tunneling spectroscopy(SR-STS) data taken over the inside and outside of the niobium island shows gradually reduced superconducting gap.