• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.352-356
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• 2003

A stoichiometric mixture of evaporating materials for $CuGaSe_2$ single crystal am films was prepared from horizontal electric furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal $CuGaSe_2$, it was found tetragonal structure whose lattice constant $a_0$ and $c_0$ were $5.615\;{\AA}\;and\;11.025\;{\AA}$, respectively. To obtain the single crystal thin films, $CuGaSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $610^{\circ}C$ and $450^{\circ}C$, respectively, The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuGaSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.24{\times}10^{16}\;cm^{-3}$ and $295\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;:\;1.7998\;eV\;-\;(8.7489\;{\times}\;10^{-4}\;eV/K)T^2(T\;+\;335\;K)$. After the as-grown $CuGaSe_2$ single crystal thin films was annealed in Cu-, Se-, and Ga-atmospheres, the origin of point defects of $CuGaSe_2$ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of $V_{CU}$, $V_{Se}$, $CU_{int}$, and $Se_{int}$, obtained by PL measurements were classified as a donors or accepters type. And we concluded that the heat-treatment in the Cu-atmosphere converted $CuGaSe_2$ single crystal thin films to an optical n-type. Also, we confirmed that Ga in $CuGaSe_2/GaAs$ did not form the native defects because Ga in $CuGaSe_2$ single crystal thin films existed in the form of stable bonds.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.953-954
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• 2006

Ti-Cu-Ni-Sn quaternary amorphous alloys of $Ti_{50}Cu_{32}Ni_{15}Sn_3$, $Ti_{50}Cu_{25}Ni_{20}Sn_5$, and $Ti_{50}Cu_{23}Ni_{20}Sn_7$ composition were prepared by mechanical alloying in a planetary high-energy ball-mill (AGO-2). The amorphization of all three alloys was found to set in after milling at 300rpm speed for 2h. A complete amorphization was observed for $Ti_{50}Cu_{32}Ni_{15}Sn_3$ and $Ti_{50}Cu_{25}Ni_{20}Sn_5$ after 30h and 20h of milling, respectively. Differential scanning calorimetry analyses revealed that the thermal stability increased in the order of $Ti_{50}Cu_{32}Ni_{15}Sn_3$, $Ti_{50}Cu_{25}Ni_{20}Sn_5$, and $Ti_{50}Cu_{23}Ni_{20}Sn_7$.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.288-294
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• 1999

In the flip chip interconnection using solder bump, the Under Bump Metallurgy (UBM) is required to perform multiple functions in its conversion of an aluminum bond pad to a solderable surface. In this study, various UBM systems such as $Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 5\mu\textrm{m}, Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}, al 1\mu\textrm{m}/Ni 0.2\mu\textrm{m} / Cu 1\mu\textrm{m} and Al 1\mu\textrm{m}/Pd 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}$ for flip chip interconnection using the low melting point eutectic 63Sn-37Pb solder were investigated and compared to their metallurgical properties. $100\mu\textrm{m}$ size bumps were prepared for using an electroplating process. The effects of the number of reflows and aging time on the growth of intermetallic compounds(IMC) were investigated. $Cu_6Sn_5$ and $Cu_3Sn$ IMC were abserved after aging treatment in the UBM system with thick coper $(Al 1\mu\textrm{m}/Ti 0.2\mu\textrm{m}/Cu 5\mu\textrm{m})$. However only the $Cu_6Sn_5$ was detected in the UBM system with $1\mu\textrm{m}$ thick copper even after 2 reflow and 7 day aging at $150^{\circ}C$. Complete Cu consumption by Cu-Sn IMC growth gives rise to a direct contact between solder inner layer such as Ti, Ni and Pd, and hence to possibly cause reactions between two of them. In this study, however, only for the Pd case, IMC of PdSn. was observed by Cu consumption. UBM interfacial reactions with s이der affected the adhesion strength ot s이der balls after s이der reflow and annealing treatment.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.28-31
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• 2012

We report the solid-liquid phase equilibria on the $GdBa_2Cu_3O_{7-{\delta}}$ (GdBCO) stability phase diagram in low oxygen pressures ($PO_2$) ranging from 1 to 100 mTorr. On the basis of the GdBCO stability phase diagram experimentally determined in low oxygen pressures, the isothermal sections of three different phase fields on log $PO_2$ vs. 1/T diagram were schematically constructed within the $Gd_2O_3-Ba_2CuO_y-Cu_2O$ ternary system, and the solid-liquid phase equilibria in each phase field were described. The invariant points on the phase boundaries include the following three reactions; a pseudobinary peritectic reaction of $GdBCO{\leftrightarrow}Gd_2O_3$ + liquid ($L_1$), a ternary peritectic reaction of $GdBCO{\leftrightarrow}Gd_2O_3+GdBa_6Cu_3O_y$ + liquid ($L_2$), and a monotectic reaction of $L_1{\leftrightarrow}GdBa_6Cu_3O_y+L_2$. A conspicuous feature of the solid-liquid phase equilibria in low $PO_2$ regime (1 - 100 mTorr) is that the GdBCO phase is decomposed into $Gd_2O_3+L_1$ or $Gd_2O_3+GdBa_6Cu_3O_y+L_2$ rather than $Gd_2BaCuO_5+L$ well-known in high $PO_2$ like air.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.196-201
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• 2023

In this study, a CNT fiber flexible electrode grafted with CuO nanoparticles (CuO NPs) and polyaniline (PANI) was developed and applied to a nonenzymatic electrochemical sensor for H₂O₂ detection. CuO NPs/PANI/CNT fiber electrode was fabricated through the synthesis and deposition of PANI and CuO NPs on the CNT fiber surface using an electrochemical method. Surface morphology and elemental composition of the CuO NPs/PANI/CNT fiber electrode were characterized by scanning electron microscope with energy dispersive X-ray spectrometry. And its electrochemical characteristics were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). Compared with a bare CNT fiber as a control group, the CuO NPs/PANI/CNT fiber electrode showed a 4.78-fold increase in effective surface area and a 8.33-fold decrease in electron transfer resistance, which leads to excellent electrochemical properties such as a good electrical conductivity and an efficient electron transfer. These improved characteristics were due to the synergistic effect through the grafting of CNT fiber, PANI and CuO NPs. As a result, this electrode enhanced the H₂O₂ sensing performance.

• Solar Energy
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• v.20 no.2
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• pp.43-54
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• 2000

We prepared and characterized $Cu(In_{1-x}Ga_x)Se_2$(CIGS) films using a elemental co-evaporation method for absorbing layer of high efficiency thin film solar cells. The CIGS films deposited on a soda-lime glass exhibited low resistivity because of higher carrier concentration. Na was accumulated at the CIGS surface and the 0 and Se were also accumulated at the surface, suggesting that oxidation is a driving force of Na accumulation. The structure of CIGS film was modified or a secondary phase was formed in the Cu-poor CIGS bulk films probably due to the incorporation of Na into Cu vacancy sites. As the Ga/(In+Ga) ratio increased, the diffraction peaks of $Cu(In_{1-x}Ga_x)Se_2$ films were shifted to larger angle and splitted, and the grain size of $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films became smaller. All $Cu_{0.91}(In_{1-x}Ga_x)Se_2$ films showed the p-type conductivity regardless of the Ga/(In+Ga) ratio. Ag/n-ZnO/i-ZnO/CdS/$Cu_{0.91}(In_{0.7}Ga_{0.3})Se_2$/Mo solar cells were fabricated. The currently best efficiency in this study was 14.48% for $0.18cm^2$ area ($V_{oc}=581.5mV,\;J_{sc}=34.88mA$, F.F=0.714).

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.282-287
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• 1998

Dependence of magnetoresistance on base pressure and deposition rates of each Fe, Co, Cu layers in the $Fe(50{\AA}/[Co(17{\AA})/Cu(24{\AA})]_20$ multilayer thin films, prepared by dc magnetron sputtering on Corning glass, were investigated. AFM analysis, X-ray diffraction analysis, vibrating sample magnetometer analysis, and magnetoresustance measurement (4-probe method) were performed. The multilayer films deposited under low base pressure increases magnetoresistance ratio by preventing oxidation. Annealing for the samples at a moderate temperature allowed larger textured grain with no loss in the periodicity. Magnetoresistance ratio of the annealed multilayers was increased due to the increase antiferromagnetically coupled fraction of the film after annealing. Optimization of deposition rate was greater than 1 $\AA$/s for Fe, and 2.8 $\AA$/s for Cu. Deposition rate of Co showed a tendency of increasing of magnetoresistance ratio due to the formation of flat magnetic layer in case of high deposition rate of Co.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.3
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• pp.149-156
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• 1992

Transformation behavior and reversible shape memory effct of Ti-Ni-Cu alloys with various Cu content has been investigated by means of electrical resistivity measurement, differential scanning calorimetry. X-ray diffraction and strain gage sensor. The transformation sequence in Ti-Ni-Cu alloys substituted by Cu for Ni up to 5at.% occurs to $B2{\leftrightarrow}B19^{\prime}$ and it proceeds in two stages by addition of 10 at.%Cu. i.e. $B2{\leftrightarrow}B19{\leftrightarrow}B19^{\prime}$. But the content of Cu increases up to 20at.%, it has been transformed in one stage ; $B2{\leftrightarrow}B19$. The shape change of Ti-40Ni-10Cu alloy which was constrain aged in circular form bended in $B2{\leftrightarrow}B19$ transformation but it spreaded out in $B19{\leftrightarrow}B19^{\prime}$ transformation. The amount of reversible shape change (${\Delta}{\varepsilon}$) of Ti-47Ni-3Cu alloy constrain aged at $400^{\circ}C$ after solution treatment has a maximum value of about $5.6{\times}10^{-3}$, but that of cold rolled and constrain aged specimens exhibits a little value independent of Cu concentrations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.258-259
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• 2005

[ $CuInSe_2$ ] thin films were fabricated at various fabrication conditions (substrate temperature, sputtering pressure, BC/RF power, vapor deposition, heat treatment). And structural and electrical properties were measured in order to certify optimum conditions for growth of the ternary compound semiconductor $CuInSe_2$ thin films with stoichiometric composition. $CuInSe_2$ thin film was well made at the heat treatment of 500[$^{\circ}C$] of SLG/Cu/In/Se stacked elemental layer which was prepared by sputter and thermal evaporator, and chemical composition of the thin film was analyzed nearly as the proportion of 1 : 1 : 2. At the same time, carrier concentration, hall mobility and resistivity of the thin films was $1.27\sim9.88\times10^{17}[cm^{-3}]$, $49.95\sim185[cm^2/V{\cdot}s]$ and $10^{-1}\sim10^{-2}[\Omega{\cdot}cm]$, respectively

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.5
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• pp.525-532
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• 1992

Fluorine-doped YBaS12TCuS13TOS17-xTFS1yT superconducting materials with y varing two orders of magnitude form 0.02 to 2.0 have been prepared by a sol-gel process by using metal nitrate salts, sodium hydroxide and sodium fluoride. Fluorine contents have been measured using an ion-selective electrode. All fluorine doped as reactant were found to be present in the resulted samples. From the observation of XRD it has been concluded that the samples with y 0.2 formed simply the single phase of perovskite structure, whereas those with y 0.5 yielded together some compounds such as BaFS12T, YFS13T and CuO in the resulted samples. The observation of solid state S019TF NMR has been carried out in order to check whether fluorine was actually incorporated into the lattice sites, and the experimental results revealed that the mole ratio of fluorine incorporated into the lattice sites of YBaS12TCuS13TOS17-xT was approximately 0.2 per mole of the compound. Also electrical resistivity measurement indicated that onset transition temperature has the tendency to increase slightly with increasing y in the dilute region as y 0.2.