• Proceedings of the Korean Vacuum Society Conference
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• 1995.02a
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• pp.36-36
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• 1995

The cubic (zinc blende) CdSe eppilayers were grown on GaAs(100) substrates by electron beam (e-beam) evapporation technique. X-ray scans with copper $K\alpha$ radiation indicate that the CdSe eppilayers are zinc blende. The lattice pparameter obtained from the (400) reflection is 6.077$\AA$, which is in excellent agreement with the value repported in the literature for zinc blende CdSe. The orientation of as-grown CdSe eppilayer is determined by electron channeling ppatterns(ECpp). The crystallinity of heteroeppitaxial CdSe layers were investigated based on the double crystal x-ray rocking curve(DCRC). The deppendence of the rocking curve width on layer thickness was studied. The FWHM(full width at half maximum) of CdSe eppilayers grown on GaAs(100) substrates is decreasing with increasing eppilayer thickness. The carrier concentration and mobility of the as-grown eppilayers deduced Hall data by van der ppauw method, are about 7$\times$1017 cm-3 and 2$\times$102 $\textrm{cm}^2$ / sec at room tempperature, resppectively. The energy gapp was determinded from the pphotocurrent sppectrum. In pphotocurrent sppectrum of a 1-${\mu}{\textrm}{m}$-thick CdSe eppilayer at 30K, the ppeak at 1.746 eV is due to the free exciton of cubic CdSe. In summary, We have shown that eppilayers of zinc blende CdSe can be grown on GaAs(100) substrates by e-beam, desppite the large mismatch between eppilayer and substrate, as well as the natural ppreference for CdSe to form in the wurtzite structure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.1
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• pp.191-196
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• 2010

Aluminum doped zinc oxide (AZO) films have been prepared on Coming 7059 glass substrates by r.f. magnetron sputtering method. A powder target instead of a conventional sintered ceramic target was used in order to improve the utilization efficiency of the target and reduce the cost of the film deposition process. The influence of sputter pressure on the structural, electrical, and optical properties of AZO films were studied. The AZO films had hexagonal wurtzite structure with a preferred c-axis orientation, regardless of sputter pressure and target types. The crystallinity and degree of orientation was increased by increasing the sputter pressure. For higher sputtering pressures, a reduction of the resistivity was observed due to a increase on the mobility and the carrier concentration. The lowest resistivity of $6.5{\times}10^{-3}\;{\Omega}-cm$ and the average transmittance of 80% can be obtained for films deposited at 15 mTorr.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.2
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• pp.104-110
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• 2001

Structural, optical and electrical properties of Cd$_{1-x}$ Zn$_{x}$S films deposited by chemical bath deposition(CBD), which is a very attractive method for low-cost and large-area solar cells, are presented. Especially, in order to control more effectively the zinc component of the films, zinc acetate, which was used as the zinc source, was added in the reaction solution after preheating the reaction solution and the pH of the reaction solution decreased with increasing the concentration of zinc acetate. The films prepared after preheating and pH control had larger zinc component and higher optical band gap. The crystal structures of Cd$_{1-x}$ Zn$_{x}$S films was a wurtzite type with a preferential orientation of the (002) plane and the lattice constants of the films changed from the value for CdS to those for ZnS with increasing the mole ratio of the zinc acetate. The minimum lattice mismatch between Cd$_{1-x}$ Zn$_{x}$S and CdTe were 2.7% at the mole ratio of (ZnAc$_2$)/(CdAc$_2$+ZnAc$_2$)=0.4. As the more zinc substituted for Cd in the films, the optical transmittance improved, while the absorption edge shifted toward a shorterwavelength. the photoconductivity of the films was higher than the dark conductivity, while the ratio of those increased with increasing the mole ratio of zinc acetate. acetate.

• Carbon letters
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• v.16 no.3
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• pp.192-197
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• 2015

In the present work, we propose a molecule (C₁₄H₁₄) that can be used as a building block of hexagonal diamond-type crystals and nanocrystals, including wurtzite structures. This molecule and its combined blocks are similar to diamondoid molecules that are used as building blocks of cubic diamond crystals and nanocrystals. The hexagonal part of this molecule is included in the C₁₂ central part of this molecule. This part can be repeated to increase the ratio of hexagonal to cubic diamond and other structures. The calculated energy gap of these molecules (called hereafter wurtzoids) shows the expected trend of gaps that are less than that of cubic diamondoid structures. The calculated binding energy per atom shows that wurtzoids are tighter structures than diamondoids. Distribution of angles and bonds manifest the main differences between hexagonal and cubic diamond-type structures. Charge transfer, infrared, nuclear magnetic resonance and ultraviolet-visible spectra are investigated to identify the main spectroscopic differences between hexagonal and cubic structures at the molecular and nanoscale. Natural bond orbital population analysis shows that the bonding of the present wurtzoids and diamondoids differs from ideal sp³ bonding. The bonding for carbon valence orbitals is in the range (2s^0.982p^3.213p^0.02)-(2s^0.942p^3.313p^0.02) for wurtzoid and (2s^0.932p^3.293p^0.01)-(2s^0.992p^3.443p^0.01) for diamantane.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.9
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• pp.717-722
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• 2012

In this work, we study on the effects of the oxygen pressure on the structural and crystalline of MgZnO thin films. MgZnO thin films were deposited on p-Si (111) substrates by using pulsed laser deposition. The X-ray diffraction analysis and energy-dispersive X-ray results revealed that as the oxygen pressure increased and Mg content in the MgZnO films decreased. Also Crystal structure was changed from cubic rock salt to hexagonal wurtzite. Alpha step and atomic force microscopy results showed that the thickness of the films are about 100 nm, and it has been found that the MgZnO (002) preferred orientation were deposited with increasing the oxygen pressure. Therefore, the effect of the preferred orientation, the crystallization grew in the form of the columnar; Grain size and RMS of the films were increased with increasing oxygen pressure.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2547-2552
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• 2010

CdS nano-particulate films were prepared at the air/water interface under Langmuir monolayers of arachidic acid (AA) via interfacial reaction between $Cd^{2+}$ ions in the subphase and $H_2S$ molecules in the gaseous phase. The films were made up of fine CdS nanoparticles with hexagonal Wurtzite crystal structure after reaction. It was revealed that the formation of CdS nano-particulate films depends largely on the experimental conditions. When the films were ripened at room temperature or an increased temperature ($60^{\circ}C$) for one day, numerous holes were appeared due to the dissolution of smaller nanoparticles and the growth of bigger nanoparticles with an improved crystallinity. When the films were ripened further, CdS rodlike nanoparticles with cubic zinc blende crystal structure appeared due to the re-nucleation and growth of CdS nanoparticles at the stacking faults and defect structures of the hexagonal CdS grains. These structures were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray diffraction (XRD). These results declare that CdS semiconductor nanoparticles formed at the air/water interface change their morphologies and crystal structures during the ripening process due to dissolution and recrystallization of the particles.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.46-50
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• 2017

The Zn1-xMnxO ($0.00{\leq}x{\leq}0.06$) samples have been synthesized in the form of powder by the coprecipitation method at low temperature using $Zn(CH_3COO)_2$. $2H_2O$ and $Mn(CH_3COO)_2$. $4H_2O$ powders, as well as HCl and $NH_4OH$ solutions as starting materials. Characterization was conducted using XRD, TEM, XRF, FTIR and VSM. The result shows that the $Zn_{(1-x)}Mn_xO$ ($0.00{\leq}x{\leq}0.06$) nanoparticles have the wurtzite phase with a hexagonal structure and particle sizes ranging from 17.48 to 118.83 nm. In a qualitative analysis of XRF, the peaks that confirm the existence of the manganese element in Mn-doped ZnO samples were observed. Meanwhile, FTIR test result shows that there are peaks at around $500cm^{-1}$ and $400cm^{-1}$ in the FTIR spectra for Mn doped ZnO samples which clearly reveal the existence of the (Zn, Mn)-O strain mode. The (Zn, Mn)-O absorption peak positions have shifted to a lower wave number with increasing Mn doping content. The peak intensity is also lower if compared to that of the ZnO sample without doping. From the VSM test, it is shown that $Zn_{(1-x)}Mn_xO$ ($0.00{\leq}x{\leq}0.06$) nanoparticles are all paramagnetic having monotonically increased susceptibility as increasing Mn content.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.290.2-290.2
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• 2014

본 연구에서는 스핀코팅방법으로 증착된 ZnO 박막의 Zn-seed 층 열처리에 따른 구조적 광학적 특성에 관한 연구를 수행하였다. ZnO 박막을 증착하기 전, Quartz 기판에 열증착법으로 Zn-seed층을 증착하였고, furnace에서 300, 350, 400, $450^{\circ}C$의 온도로 1시간 동안 열처리하였다. ZnO 박막은 스핀코팅방법으로 5층을 증착한 후, $600^{\circ}C$에서 1시간 동안 후열처리를 하였다. X-ray diffractometer, UV-visible spectrometer, Photoluminescence를 이용하여 ZnO 박막의 구조적, 광학적 특성을 분석하였다. 모든 ZnO 박막 시료에서 c-축 배향성을 나타내는 강한 ZnO(002)피크와 ZnO(100), ZnO(101) 회절피크가 나타났고, wurtzite 형태의 ZnO 박막이 관찰되었다. Zn-seed층을 $350^{\circ}C$에서 열처리함에 따라 deep-level emission 피크에 대한 near-band-edge emission 피크의 발광세기 비율이 증가하였으나, 온도가 증가함에 따라 점점 감소하였다. 또한, Zn-seed층을 $350^{\circ}C$에서 열처리 하였을 때 가장 높은 광 투과도를 나타내었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.434.2-434.2
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• 2014

We observe enhanced pH response of solution-gated field-effect transistors (SG-FET) having 1D-2D hybrid channel of vertical grown ZnO nanorods grown on CVD graphene (Gr). In recent years, SG-FET based on Gr has received a lot of attention for biochemical sensing applications, because Gr has outstanding properties such as high sensitivity, low detection limit, label-free electrical detection, and so on. However, low-defect CVD Gr has hardly pH responsive due to lack of hydroxyl group on Gr surface. On the other hand, ZnO, consists of stable wurtzite structure, has attracted much interest due to its unique properties and wide range of applications in optoelectronics, biosensors, medical sciences, etc. Especially, ZnO were easily grown as vertical nanorods by hydrothermal method and ZnO nanostructures have higher sensitivity to environments than planar structures due to plentiful hydroxyl group on their surface. We prepared for ZnO nanorods vertically grown on CVD Gr (ZnO nanorods/Gr hybrid channel) and to fabricate SG-FET subsequently. We have analyzed hybrid channel FETs showing transfer characteristics similar to that of pristine Gr FETs and charge neutrality point (CNP) shifts along proton concentration in solution, which can determine pH level of solution. Hybrid channel SG-FET sensors led to increase in pH sensitivity up to 500%, compared to pristine Gr SG-FET sensors. We confirmed plentiful hydroxyl groups on ZnO nanorod surface interact with protons in solution, which causes shifts of CNP. The morphology and electrical characteristics of hybrid channel SG-FET were characterized by FE-SEM and semiconductor parameter analyzer, respectively. Sensitivity and sensing mechanism of ZnO nanorods/Gr hybrid channel FET will be discussed in detail.

• Korean Journal of Materials Research
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• v.21 no.9
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• pp.486-490
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• 2011

Nano-indium-coated ZnO:In thick films were prepared by a hydrothermal method. ZnO:In gas sensors were fabricated by a screen printing method on alumina substrates. The gas sensing properties of the gas sensors were investigated for hydrocarbon gas. The effects of the indium concentration of the ZnO:In gas sensors on the structural and morphological properties were investigated by X-ray diffraction and scanning electron microscopy. XRD patterns revealed that the ZnO:In with wurtzite structure was grown with (1 0 0), (0 0 2), and (1 0 1) peaks. The quantity of In coating on the ZnO surface increased with increasing In concentration. The sensitivity of the ZnO:In sensors was measured for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity to $CH_4$ gas and $CH_3CH_2CH_3$ gas of the ZnO:In sensors was observed at the In 6 wt%. The response and recovery times of the 6 wt% indiumcoated ZnO:In gas sensors were 19 s and 12 s, respectively.