• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
• /
• pp.20-20
• /
• 2007

Nanowire-based field-effect transistors (FETs) decorated with nanoparticles have been greatly paid attention as nonvolatile memory devices of next generation due to their excellent transportation ability of charge carriers in the channel and outstanding capability of charge trapping in the floating gate. In this work, top-gate single ZnO nanowire-based FETs with and without Au nanoparticles were fabricated and their memory effects were characterized. Using thermal evaporation and rapid thermal annealing processes, Au nanoparticles were formed on an $Al_2O_3$ layer which was semi cylindrically coated on a single ZnO nanowire. The family of $I_{DS}-V_{GS}$ curves for the double sweep of the gate voltage at $V_{DS}$ = 1 V was obtained. The device decorated with nanoparticles shows giant hysterisis loops with ${\Delta}V_{th}$ = 2 V, indicating a significant charge storage effect. Note that the hysterisis loops are clockwise which result from the tunneling of the charge carriers from the nanowire into the nanoparticles. On the other hand, the device without nanoparticles shows a negligible countclockwise hysterisis loop which reveals that the influence of oxide trap charges or mobile ions is negligible. Therefore, the charge storage effect mainly comes from the nanoparticles decorated on the nanowire, which obviously demonstrates that the top-gate single ZnO nanowire-based FETs decorated with Au nanoparticles are the good candidate for the application in the nonvolatile memory devices of next generation.

• 한국재료학회지
• /
• 제29권3호
• /
• pp.196-203
• /
• 2019

We report on the fabrication and characterization of an oxide photoanode with a zinc oxide (ZnO) nanorod array embedded in cuprous oxide ($Cu_2O$) thin film, namely a $ZnO/Cu_2O$ oxide p-n heterostructure photoanode, for enhanced efficiency of visible light driven photoelectrochemical (PEC) water splitting. A vertically oriented n-type ZnO nanorod array is first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type $Cu_2O$ thin film is directly electrodeposited onto the vertically oriented ZnO nanorod array to form an oxide p-n heterostructure. The introduction of $Cu_2O$ layer produces a noticeable enhancement in the visible light absorption. From the observed PEC current density versus voltage (J-V) behavior under visible light illumination, the photoconversion efficiency of this $ZnO/Cu_2O$ p-n heterostructure photoanode is found to reach 0.39 %, which is seven times that of a pristine ZnO nanorod photoanode. In particular, a significant PEC performance is observed even at an applied bias of 0 V vs $Hg/Hg_2Cl_2$, which makes the device self-powered. The observed improvement in the PEC performance is attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential including the light absorption and separation processes of photoinduced charge carriers, which provides a new avenue for preparing efficient photoanodes for PEC water splitting.

• 한국분말재료학회지
• /
• 제28권3호
• /
• pp.239-245
• /
• 2021

The SnSe single crystal shows an outstanding figure of merit (ZT) of 2.6 at 973 K; thus, it is considered to be a promising thermoelectric material. However, the mass production of SnSe single crystals is difficult, and their mechanical properties are poor. Alternatively, we can use polycrystalline SnSe powder, which has better mechanical properties. In this study, surface modification by atomic layer deposition (ALD) is chosen to increase the ZT value of SnSe polycrystalline powder. SnSe powder is ground by a ball mill. An ALD coating process using a rotary-type reactor is adopted. ZnO thin films are grown by 100 ALD cycles using diethylzinc and H₂O as precursors at 100℃. ALD is performed at rotation speeds of 30, 40, 50, and 60 rpm to examine the effects of rotation speed on the thin film characteristics. The physical and chemical properties of ALD-coated SnSe powders are characterized by scanning and tunneling electron microscopy combined with energy-dispersive spectroscopy. The results reveal that a smooth oxygen-rich ZnO layer is grown on SnSe at a rotation speed of 30 rpm. This result can be applied for the uniform coating of a ZnO layer on various powder materials.

• 한국건축시공학회지
• /
• 제21권6호
• /
• pp.519-527
• /
• 2021

본 연구에서는 기존의 전자기파 차폐 성능이 없는 콘크리트를 대상으로 아크 금속용사 공법을 적용하여 전자기파 차폐성능을 확보하고자 한다. 이를 위해 금속 코팅의 두께에 전기적 특성을 평가하기 위해서 8 종류의(Cu, CuAl, CuNi, CuZn, Al, Zn, ZnAl, AlMg) 금속들을 두께 100, 200 및 500㎛의 금속 코팅으로 제작하여 4pin-probe로 표면에서의 전기전도도를 측정하였고, KS C 0304에 의거하여 전자기파 차폐 성능 시험을 실시하였다. 금속 코팅 시험 결과를 토대로 전자기파 차폐를 위한 최적의 금속 코팅 두께 200㎛를 제안하였으며, 이를 300×300×100mm 콘크리트 시험체에 용사하여 전자기파 차폐 성능을 분석한 결과 목표 성능 1GHz에서 80dB의 전자기파 차폐 성능이 확보됨을 확인하였다. 하지만 부착 강도의 경우 최대 1.11MPa로 목표 성능 대비 74% 이하로 확인되어 추후 콘크리트 표면에 미세한 요철을 형성하여 부착 성능을 향상시키는 연구가 필요할 것으로 판단된다.

• 산업기술연구
• /
• 제27권A호
• /
• pp.19-24
• /
• 2007

This research was done for possible treatment of impermeable surfaces rainwater runoff containing heavy metal ions by manganese oxide coated on polypropylene support. Manganese oxide was coated by Birnessite Coating Methods(BCM)and the coating analyzed by SEM and FT-IR techniques. The efficiency of heavy metal ions adsorption was also assessed via both batch and column tests. Adsorption efficiencies of Cd, Zn, Cu, and Pb were 99.4%, 98.9%, 96.7%, and over 95.7%, respectively. The adsorption progress pattern reveals quite fast adsorption at initial periods of treatment and change to slower rates at later times.

• Korean Journal of Chemical Engineering
• /
• 제35권11호
• /
• pp.2303-2312
• /
• 2018

Pretreatment process of silica-coated PET fabrics, a major low-grade PET waste, was developed using the reaction with NaOH solution. By destroying the structure of silica coating layer, impurities such as silica and pigment dyes could be removed. The removal of impurity was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The pretreated PET fabric samples were used for depolymerization into its monomer, bis(2-hydroxylethyl) terephthalate (BHET), by glycolysis with ethylene glycol (EG), and zinc acetate (ZnAc) catalyst. The quality of BHET was confirmed by DSC, TGA, HPLC and NMR analyses. The highest BHET yield of 89.23% was obtained from pretreated PET fabrics, while glycolysis with raw PET fabric yielded 85.43%. The BHET yield from untreated silica-coated PET fabrics was 60.39%. The pretreatment process enhances the monomer yield by the removal of impurity and also improves the quality of the monomer.

• Journal of Welding and Joining
• /
• 제15권6호
• /
• pp.49-56
• /
• 1997

Effect of process parameters on the quality of condenser discharge weld for coated sheet steels was discussed. The welding specimens were coated with pure Zn of 20/20 g/m2 in the production line. Direct measurements of welding parameters such as the discharge current, the pressures and the voltage drop across the electrodes were carried out with welding process monitoring system. High speed camera was also utilized to analyze the weld formation process. Test results indicated that the relation between weld strength and applied energy was stabilized at the acceptable welding heat input range. It was thought that the acceptable welding heat input should be redefined based on the monitored data because the calculated value of the welding heat input could hardly be utilized if the discharge condition was changed. Mechanical test results and high speed photographs showed that expulsion deteriorated the weld quality and the strength at the same time especially when the size of the spatter was large enough to carry the molten metal, which should form the nugget, out of the welding spot. Results also demonstrated that the discharge current should be applied at the appropriate time during the process because sufficient nugget was not produced if the time was deviated from the optimum range.

• 한국해양공학회지
• /
• 제25권1호
• /
• pp.39-43
• /
• 2011

This study has lowered the specific resistance by coating a thin film layer of Ag, playing the role of the electron donor on the ZnO that is used usefully for the transparent conductive oxides. Presently, this study has examined the transmittance and electric characteristics according to the thickness of the Ag thin film layer. Also, this study has observed the transmittance and electric characteristics according to the uppermost ZnO thin film layer of ZnO/Ag/ZnO symmetric film and has conducted the theoretical investigation. In order to observe the transmittance and electric characteristics according to the thickness of the Ag thin film layer and the uppermost ZnO thin film layer, this study conducted the film deposition at room temperature while making use of the DC magnetron sputtering system. In order to see the changes in the thickness of the Ag thin film layer, this study coated a thin film while increasing by 4nm; and, in order to see the changes in the thickness of uppermost ZnO thin film layer, it performed the thin film coating by increasing by 5nm. From the experimental result, the researchers observed that the best transmittance could be obtained when the thickness of the Ag thin film layer was 8nm, but the resistance and mobility increased as the thickness got larger. On the other hand, when the thickness of the uppermost ZnO thin film layer was 20nm, the experiment yielded the best transmittance with excellent electric characteristics. Also, when compared the ZnO/Ag asymmetric film with the ZnO/Ag/ZnO symmetric film, the ZnO/Ag asymmetric film showed better transmittance and electric characteristics.

• 한국전자파학회논문지
• /
• 제26권1호
• /
• pp.101-112
• /
• 2015

II~VI족 화합물 반도체 $Zn_xCd_{1-x}S$ 박막을 Indium-tin-oxide(ITO)가 도포된 유리기판 상에 열증발법을 사용하여 증착하였다. 박막의 합성비(molar ratio) x($0{\leq}x{\leq}1$)는 CdS(x=0) 박막과 ZnS(x=1) 박막을 포함하여, 삼원화합물 $Zn_xCd_{1-x}S$ 박막을 제조하기 위하여 변화시켰다. 또한, 증착한 박막의 결정성을 높이기 위하여 진공전기로에서 열처리 하였으며, 분광학적 특성조사를 위해서는 $400^{\circ}C$에서 열처리한 $Zn_xCd_{1-x}S$ 박막이 최적임을 알았다. $Zn_xCd_{1-x}S$ 박막의 합성비(x)와 전자적 구조를 조사하기 위하여 X-선 광전자 분광법(XPS)을 사용하였고, 박막시료의 광학적 에너지 띠 간격 $E_g$는 자외선-가시광-근접 적외선(UV-Vis-NIR) 분광법으로 측정하였으며, 합성비(x)값이 0에서 1까지 변화함에 따라 2.44~3.98 eV 범위의 값을 보여주었다. 끝으로, THz-TDS(Time Domain Spectroscopy) 시스템을 사용하고 $Zn_xCd_{1-x}S$ 박막의 THz파 특성을 측정하여 테라헤르츠(THz) 영역용 전자 및 광학 소자로서 응용가능성을 확인하였다.

• Journal of Welding and Joining
• /
• 제23권3호
• /
• pp.61-67
• /
• 2005

Since lead (Pb)-free solders for electronics have higher melting points than that of eutectic Sn-Pb solder, they need higher soldering temperatures. In order to decrease the soldering temperature we tried to coat Sn-Bi layer on $Sn-3.5\%Ag$ solder by electroplating, which applies the mechanism of transient liquid phase bonding to soldering. During heating Bi will diffuse into the $Sn-3.5\%Ag$ solder and this results in decreasing soldering temperature. As bonding samples, the 1608 capacitor electroplated with Sn, and PCB, its surface was finished with electroless-plated Ni/Au, were selected. The $Sn-95.7\%Bi$ coated Sn-3.5Ag was supplied as a solder between the capacitor and PCB land. The samples were reflowed at $220^{\circ}C$, which was lower than that of normal reflow temperature, $240\~250^{\circ}C$, for the Pb-free. As experimental result, the joint of $Sn-95.7\%Bi$ coated Sn-3.5Ag showed high shear strength. In the as-reflowed state, the shear strength of the coated solder showed 58.8N, whereas those of commercial ones were 37.2N (Sn-37Pb), 31.4N (Sn-3Ag-0.5Cu), and 40.2N (Sn-8Zn-3Bi). After thermal shock of 1000 cycles between $-40^{\circ}C$ and $+125^{\circ}C$, shear strength of the coated solder showed 56.8N, whereas the previous commercial solders were in the range of 32.3N and 45.1N. As the microstructures, in the solder $Ag_3Sn$ intermetallic compound (IMC), and along the bonded interface $Ni_3Sn_4$ IMC were observed.