• 한국재료학회지
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• 제20권4호
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• pp.199-203
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• 2010

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at $400^{\circ}C$ under an $N_2/O_2$ atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from $400^{\circ}C$ to $600^{\circ}C$. The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under $500^{\circ}C$, while nanowire structures begin to form on the beads above $600^{\circ}C$. The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of $2.0\;V/{\mu}m$ was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

• 한국전기전자재료학회논문지
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• 제24권2호
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• pp.162-165
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• 2011

In this paper, $CuInSe_2$ thin film was prepared by use of the co-evaporation method with the variation of the substrate temperature in the range of $100^{\circ}C$ to $400^{\circ}C$. The film was annealed at $300^{\circ}C$ for an hour in a vacuum chamber at $3{\times}10-4$ Pa. After annealing, the thin film prepared at the substrate temperatures of $100^{\circ}C$ and $200^{\circ}C$ was observed. The XRD (x-ray diffraction) pattern of sample prepared at $100^{\circ}C$ showed the single phase formation of $CuInSe_2$. However, at $200^{\circ}C$, there was no apparent difference in the XRD pattern except a variation in the intensity of the peak. As the annealing treatment of substrate improved the crystal structure of the film, it affected to the increase of an electron mobility, resulted in an increase in conductivity and a decrease in resistance. As a results, when the substrate temperature was at $200^{\circ}C$ and $300^{\circ}C$, the sheet resistance was 1.534 $\Omega/\Box$ and 1.554 $\Omega/\Box$, respectively, and the resistivity was $1.76{\times}10-6\;{\Omega}{\cdot}cm$ and $1.7210-6\;{\Omega}{\cdot}cm$, respectively. From the absorption spectrum measurements, there was no variation between the before and after annealing conductions. And it means that the annealing step does not affect the thickness of the thin film.

• Progress in Superconductivity
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• 제9권1호
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• pp.102-106
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• 2007

YBCO films have been synthesized using a spray pyrolysis method. We used nitrates of Y, Ba, Cu as precursors. Deposition was made on $LaAlO_3$ (100) single crystal substrate by spraying the mist of aqueous precursor solution generated by a concentric nozzle. The distance between concentric nozzle and substrate was 15 cm. C-axis oriented films were obtained at deposition temperature of $740{\sim}800^{\circ}C$ and working pressure of 20 Torr. Oxygen partial pressure was 3 Torr and substrate was transported with the speed ranging from 0.23 cm/min to 0.7 cm/min by reel to reel. Scanning electron microscope (SEM) and X-ray diffraction (XRD) observation revealed that films are smooth and highly textured with (001) planes parallel to substrate. Highest critical current density (Jc) was $1.38\;MA/cm^2$ at 77K and self-field for the film with a thickness of $0.5\;{\mu}m$ prepared at a substrate temperature of $780^{\circ}C$ and $PO_2\;=3\;Torr$. The effect of temperature on the microstructure and YBCO phase formation will be discussed.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3695-3702
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• 2013

A nickel(II) complex $[Ni(H_2biim)_2(H_2O)_2](ClO_4)_2{\cdot}H_2O$ (1) of biimidazole ligand has been synthesized and characterized (Where $H_2biim$ = 2,2'-biimidazole). The single crystal X-ray diffraction of the complex shows a dimeric structure with six coordinated psudo-octahedral geometry. The cyclic voltammograms of complex exhibited one quasireversible reduction wave ($E_{pc}=-0.61V$) and an irreversible oxidation wave ($E_{pa}=1.28V$) in DMF solution. The interaction of the complex with Calf-Thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy. The complex is an avid DNA binder with a binding constant value of $1.03{\times}10^5M^{-1}$. The results suggest that the nickel(II) complex bind to CT-DNA via intercalative mode and can quench the fluorescence intensity of EB bind to CT-DNA with $K_{app}$ value of $3.2{\times}10^5M^{-1}$. The complex also shown efficient oxidative cleavage of supercoiled pBR322 DNA in the presence of hydrogen peroxide as oxidizing agent. The DNA cleavage by complex in presence of quenchers; viz. DMSO, KI, $NaN_3$ and EDTA reveals that hydroxyl radical or singlet oxygen mechanism is involved. The complex showed invitro antimicrobial activity against four bacteria and two fungi. The antimicrobial activity was nearer to that of standard drugs and greater than that of the free ligand.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.79-79
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• 2008

We report the growth of $Ba_{0.5}Sr_{0.5}TiO_3$(BST) thin films and their substrate-dependent electrical characteristics. BST thin films were deposited on alumina(non-single crystal), $Al_2O_3$(100) substrates by Nd:YAG Pulsed Laser Deposition(PLD) with a 355nm wavelength at substrate temperature of $700^{\circ}C$ and post-deposition annealing at $750^{\circ}C$ in flowing $O_2$ atmosphere for 1hours. BST materials had been chosen due to high dielectric permittivity and tunability for high frequency applications, To analyze the oxygen partial pressure effects, deposited films at 1, 10, 50, 100, 150, 200, 300 mTorr. The effects of oxygen pressure on structural properties of the deposited films have been investigated by X-ray diffraction(XRD) and atomic force microscope(AFM), respectively. Then we manufactured a inter-digital capacitor(IDC) patterns twenty fingers and $10{\mu}m$ gap, $700{\mu}m$ length and electrical properties were characterized. The results provide a basis for understanding the growth mechanisms and basic structural and electrical properties of BST thin films as required for tunable microwave devices applications such as varactors and tunable filters.

• Bulletin of the Korean Chemical Society
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• 제32권7호
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• pp.2351-2357
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• 2011

Three new metal-organic copper(II) complexes, $[Cu(H_2PZTC)_2]_n{\cdot}2nH_2O$ (1), $[Cu(HPZTC){\cdot}2H_2O]_n{\cdot}2nH_2O$ (2), and $Cu_2[(PZHD)(OH)(H_2O)_2]_n$ (3) ($H_3PZTC$ = pyrazine-2,3,5-tricarboxylic acid, $PZHD^{3-}$ = 2-hydroxypyrazine-3,5-dicarboxylate), have been synthesized from $Cu(II)/H_3PZTC$ system under different synthetic conditions, and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and thermogravimetric analysis. In complexes 1 and 2, $H_3PZTC$ ligands loose one and two protons, which were transformed into $H_2PZTC^-$ anion and $HPZTC^{2-}$ dianion under different preparation condition, respectively. Furthermore, two ligands coordinate with Cu(II) cations in different modes, leading to the formation of the different chain structures. In complex 3, $H_3PZTC$ ligand was converted into a new ligand-PZHD by in situ decarboxylation and hydroxylation under a higher pH value than that for complexes 1 and 2. PZHD ligands link the Cu(II) cations to form a 2D layer structure. These results demonstrate that the preparation conditions, including pH value and reaction temperature etc, play an important role in the construction of complexes based on $H_3PZTC$ ligand.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4321-4326
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• 2011

A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: $(pqx)_2Ir(acac)$ (1), $(dmpqx)_2Ir(acac)$ (2) and $(dfpqx)_2Ir(acac)$ (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4-dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with ${\mu}$-chloride-bridged dimeric iridium complex, $[(C\^N)_2Ir({\mu}-Cl)]_2$, gives a complex 1 and an unusual hydridoiridium(III) complex, $(pqx)IrH(acac)_2$ (4). The complex 1, 2 and 3 show their emissions in an orangered region (${\lambda}_{PL,max}$ = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from $^3MLCT$ states with little admixture of ligand-based $^3({\pi}-{\pi}^*)$ excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2086-2092
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• 2014

Two novel coordination compounds $[Cu_2(pypya)_3(H_2O)_2]{\cdot}Cl{\cdot}(H_2O)_5$ (1) and $\{[Cd(pypya)(ta)_{1/2}]{\cdot}H_2O\}_n$ (2) (Hpypya=2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetic acid, $H_2ta$=terephthalic acid) were synthesized and characterized by single X-ray diffraction. Structure determination reveals that complex 1 and complex 2 crystallize in the triclinic system, with the P-1 space group. The asymmetric unit of 1 contains two Cu(II) ions, and their coordination modes are different. These units of complex 1 are linked together via hydrogen bonds and ${\pi}-{\pi}$ interactions, and the 3D structure of complex 1 was formed. Complex 2, a mononuclear Cd(II) coordination compound, has a 2D structure which was constructed via coordination bonds. TGA and fluorescence spectra analysis of complex 1 and complex 2 have also been studied. In addition, the geometry parameters of complex 1 have been optimized with the B3LYP method of density functional theory (DFT) to explain its coordination behavior. The electronic properties of the complex 1 and ligand Hpypya have been investigated based on the nature bond orbital (NBO) analysis at the B3LYP level of theory. The result verifies that the synergistic effect have occurred in the compound.

• 한국방사선학회논문지
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• 제12권1호
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• pp.17-22
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• 2018

다층박막거울은 규소나 게르마늄과 같은 단결정 회절소자를 대체할 수 있는 광학소자로 수 나노미터 두께의 인공적인 회절 평면을 갖는다. 작은 두께 주기를 갖는 W/Si 다층박막거울에서 박막의 두께 변화에 따른 첫 번째 브래그 각도 및 반사율 저하를 조사하였다. 작은 두께 주기를 갖는 W/Si 다층박막거울은 $0.55^{\circ}$ 및 17.5 keV에서 최대 반사율을 나타내도록 설계되었고 72.67%의 반사율을 보였다. 텅스텐 및 규소의 박막 두께가 동일하게 변화되었을 때 첫 번째 브래그 각도의 변화 및 반사율 저하가 관찰되었다. 다층박막거울에서 텅스텐 박막중 하나의 층에서만 두께 변화가 있을 때는 반사율의 변화는 없지만 포락선의 요철이 관찰되었다. 무작위적인 가우시안 두께 변화에서도 반사율 저하가 관찰되었다. 작은 두께 주기를 갖는 W/Si 다층박막거울에서 두께 변화에 따른 반사율의 저하를 통해 제작되는 다층박막거울의 공차를 예측할 수 있을 것이다.

• Progress in Superconductivity
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• 제8권1호
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• pp.93-97
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• 2006

YBCO films were deposited on a moving substrate by a spray pyrolysis method using nitrate aqueous solution as precursors. Deposition was made on $LaAlO_3$(100) single crystal substrate by spraying precursor droplets generated by a concentric nozzle. The cation ratio of precursor solution was Y:Ba:Cu=1:2.65:4.5. The distance between nozzle and substrate was 15 cm. Substrate was transported with a speed ranging from 0.23 cm/min to 0.5 cm/min. Films were deposited at the pressure ranging from 10 Torr to 20 Torr and the deposition temperature was ranged from $740^{\circ}C\;to\;790^{\circ}C$. Oxygen partial pressure was controlled between 1 Tow and S Torr. Superconducting YBCO films were obtained from $740^{\circ}C\;to\;790^{\circ}C$ with an oxygen partial pressure of 3 Torr. Scanning electron microscope(SEM) and X-ray diffraction(XRD) observation revealed that films are smooth and highly texture with(001) plans parallel to substrate plane. Highest Jc was 0.72 $MA/cm^2$ at 77K and self-field for the film with a thickness of 0.15 m prepared at a substrate temperature of $740^{\circ}C$ and $PO_2$=3 Torr.