• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.561-561
• /
• 2012

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as fast electron mobility, high thermal conductivity and optical transparency, and also found many applications such as field-effect transistors (FET), energy storage and conversion, optoelectronic device, electromechanical resonators and chemical sensors. Several techniques have been developed to form the graphene. Especially chemical vapor deposition (CVD) is a promising process for the large area graphene. For the electrically isolated devices, the graphene should be transfer to insulated substrate from Cu or Ni. However, transferred graphene has serious drawback due to remaining polymeric residue during transfer process which induces the poor device characteristics by impurity scattering and it interrupts the surface functionalization for the sensor application. In this study, we demonstrate the characteristics of solution-gated FET depending on the removal of polymeric residues. The solution-gated FET is operated by the modulation of the channel conductance by applying a gate potential from a reference electrode via the electrolyte, and it can be used as a chemical sensor. The removal process was achieved by several solvents during the transfer of CVD graphene from a copper foil to a substrate and additional annealing process with H2/Ar environments was carried out. We compare the properties of graphene by Raman spectroscopy, atomic force microscopy(AFM), and X-ray Photoelectron Spectroscopy (XPS) measurements. Effects of residual polymeric materials on the device performance of graphene FET will be discussed in detail.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.450-450
• /
• 2011

This study reports the hydrogen sulfide gas sensing properties of ZnO nanorods bundle and the investigation of gas sensing mechanism. Also the improvement of sensing properties was also studied through the application of ZnO heterstructured nanorods. The 1-Dimensional ZnO nano-structure was synthesized by hydrothermal method and ZnO nano-heterostructures were prepared by sonochemical reaction. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectra confirmed a well-crystalline ZnO of hexagonal structure. The gas response of ZnO nanorods bundle sensor increased with increasing temperature, which is thought to be due to chemical reaction of nanorods with gas molecules. Through analysis of X-ray photoelectron spectroscopy (XPS), the sensing mechanism of ZnO nanorods bundle sensor was explained by well-known surface reaction between ZnO surface atoms and hydrogen sulfide. However at high sensing temperature, chemical conversion of ZnO nanorods becomes a dominant sensing mechanism in current system. In order to improve the gas sensing properties, simple type of gas sensor was fabricated with ZnO nano-heterostructures, which were prepared by deposition of CuO, Au on the ZnO nanorods bundle. These heteronanostructures show higher gas response and higher current level than ZnO nanorods bundle. The gas sensing mechanism of the heteronanostructure can be explained by the chemical conversion of sensing material through the reaction with target gas.

• 한국분말재료학회지
• /
• 제22권6호
• /
• pp.432-437
• /
• 2015

The en-riched $^{58}Ni$ powders are dissolved in acid solution and coated on a Cu target for proton irradiation at cyclotron to produce $^{57}Co$ radioisotope. The condition of the plating bath and the coating process are determined using the en-riched powders. To establish the coating conditions for $^{57}Co$, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a rhodium plate. The thermal diffusion of electroplated Co into a rhodium matrix was studied to apply a $^{57}Co$ Mssbauer source. The diffusion depth from surface to matrix of Co is depended on the annealing temperature and time. The deposited Co atoms diffuse completely into a rhodium (Rh) matrix without substantial loss at an annealing temperature of 1200 for 4 hours.

• 한국마이크로전자및패키징학회:학술대회논문집
• /
• 한국마이크로전자및패키징학회 2002년도 춘계 기술심포지움 논문집
• /
• pp.183-188
• /
• 2002

With the contact pad consisted of $0.5{\mu}{\textrm}{m}$ $Au/5{\mu}{\textrm}{m}$ Ni/Cu layers on a conventional ball grid array(BGA) substrate, metallurgical reaction properties between the pad and In-15(wt.%)Pb-5Ag solder alloy were studied after reflow and solid aging. In as-reflow condition, thin AuIn$_2$or Ni$_{28}$In$_{72}$ intermetallic layer was formed at the solder/pad interface according to reflow time. Dissolution of the Au layer into the molten solder was remarkably limited in comparison with eutectic Sn-37Pb alloy. After solid aging of 300 hrs, thickness of In-Ni layer increased to about $2{\mu}{\textrm}{m}$ in the both as-reflow case. It was observed that In atoms diffuse through the AuIn$_2$phase to react with underlaying Ni layer. The metallurgical reaction properties between In-l5Pb-7Ag alloy and Au/Ni surface finish were analysed to result in suppression of Au-embrittlement in the solder joints.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2006년도 추계학술대회 논문집 광주전남지부
• /
• pp.33-34
• /
• 2006

The effects of Ba and Ce addition has been investigated in YBCO prepared by trifluoroacetate (TFA) metalorganic depostition (MOD) method. Precursor solutions with cation ratios of Y:Ba:Cu:Ce = 1:2+x:3:x (x = 0, 0.05, 0.1 and 1.5) have been prepared by adding an excess amount of cerium and barium. Coated film was calcined at lower temperature and conversion heat treatment at temperature of $780{\sim}810^{\circ}C$. It has been shown that the critical current (Ic) of YBCO film was degraded by doping of Ba and Ce atoms. But Ic was increased as the amount of doped Ba and Ce content increased from 5 % to 15 %. It was observed that there was little increase of a flux pinning force with Ba and Ce addition in YBCO film prepared by TFA-MOD process.

• 한국표면공학회지
• /
• 제27권5호
• /
• pp.292-302
• /
• 1994

Alloy deposits of 80Sn-20Pb, electroplated on Cu-based leadframe alloy from an organic sulfonate bath were aged at $150^{\circ}C$ to form intermetallic phases between substrate and deposit, and effects of the deposit morphology, influenced by deposition conditions, on the fracture resistance of the 80Sn-20Pb deposit aged at $150^{\circ}C$ were examined. The growth rate of intermetallic compound layer on aging depended on the microstructure of deposit ; it was fastest in deposit formed using pulse current in bath without grain refining additive, but slowest in deposit formed using dc current in bath containing grain refining additive in spite of similar structure with equivalent grain size. The grain refining additive incorporated in electrodeposit appears to inhibit diffusion of atoms on aging, resulting in slow growth of intermetallic layer in the thickness direction but substantial growth in the lateral one. Density of surface cracks that were occurring when samples were subjected to the $90^{\circ}$-bending test increased with increasing the thickness of intermatallic layer on aging. For the same aged samples, the surface crack density of the sample electrodeposited from a bath containing the grain refining additive was the least due to the inhibiting effect of the additive incorporated into the deposit during electrolysis on atomic diffusion.

• 대한화학회지
• /
• 제18권5호
• /
• pp.329-340
• /
• 1974

X-선 회절법을 이용하여 sulfadiazine, $C_{10}H_{10}N_4O_2S$, 의 결정 및 분자 구조를 규명하였다. Acetone 과 ethanol의 혼합용액으로 부터 얻은 결정은 일사축계에 속하며, 단위세포에는 4분자가 있고, 공간군은 P21/c이다. 단위세포 상수는 $a=13.71{\pm}0.04,\;b=5.84{\pm}0.03,\;c=15.11{\pm}0.05{\AA},\;{\beta}=115.0{\pm}0.3^{\circ}$이다. 결정구조는 3차원적인 와이센버그사진으로 부터 얻어진 실험치를 이용하여 패터슨합성과 프리에합성을 하고 이를 해석하여 밝혀냈다. 수소원자를 제외한 원자들의 좌표치는 최소자승법으로 정밀화 하였으며, 최종 R값은 관측된 1517개의 독립반사에 대하여 0.15이다. 벤젠고리와 피리미딘고리의 두 평면이 이루는 각은 $76^{\circ}$이고, S-N(1)결합을 중심으로 한 N(1)-C(1) 결합과 S-C(5)결합이 이루는 conformational angle은 $77^{\circ}$로서 gauche형을 하고 있다. 이미노기의 질소원자, N(1)은 대칭중심에 의하여 옮겨지는 다른 분자의 피리미딘고리의 질소원자, N(3)와 $N-H{\cdots}N$형의 수소결합을 이루고 있으며, 아미노기의 질소원자, N(4)는 b축의 거리만큼 떨어져 있는 다른분자의 산소원자, O(1) 및 O(2)와 두개의 $N-H{\cdots}O$형 수소결합을 이루고 있다. 이들 수소결합의 2차원적 그물은 (100)면에 평행한 무한한 분자층을 형성하며 인접분자층 사이에는 van der Waals의 힘에 의하여 결합되어 있다

• 대한화학회지
• /
• 제59권3호
• /
• pp.215-224
• /
• 2015

Unsymmetrical tetradentate Schiff base N-(2-hydroxy-5-methylacetophenone)-N'-(2-hydroxy acetophenone) ethylene diamine (H₂L) and its complexes with Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, IR, electronic spectra and thermogravimetric analyses. ¹H, ¹³C-NMR and FAB Mass spectra of ligand clearly indicate the presence of OH and azomethine groups. Elemental analyses of the complexes indicate that the metal to ligand ratio is 1:1 in all complexes. Infrared spectra of complexes indicate a dibasic quadridentate nature of the ligand and its coordination to metal ions through phenolic oxygen and azomethine nitrogen atoms. The thermal behavior of these complexes showed the loss of lattice water in the first step followed by decomposition of the ligand in subsequent steps. The thermal data have also been analyzed for the kinetic parameters by using Horowitz-Metzger method. The dependence of the electrical conductivity on the temperature has been studied over the temperature range 313-403 K and the complexes are found to show semiconducting behavior. XRD and SEM images of some representative complexes have been recorded. The antimicrobial activity of the ligand and its complexes has been screened against various microorganisms and all of them were found to be active against the test organisms. The Fe(III) and Ni(II) complex have been tested for the catalytic oxidation of styrene.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.218-218
• /
• 2012

Recently, hexagonal manganites have attracted much attention because of the coexistence of ferroelectricity and antiferromagnetic (AFM) order. The crystal structure of hexagonal manganites consists of $MnO_5$ polyhedra in which $Mn^{3+}$ ion is surrounded by three oxygen atoms in plane and two apical oxygen ions. The Mn ions within Mn-O plane form a triangular lattice and couple the spins through the AFM superexchange interaction. Due to incomplete AFM coupling between neighboring Mn ions in the triangular lattice, the system forms a geometrically-frustrated magnetic state. Among hexagonal manganites, $YMnO_3$, in particular, is the best known experimentally since the f states are empty. In addition, for applications, $YMnO_3$ thin films have been known as promising candidates for non-volatile ferroelectric random access memories. However, $YMnO_3$ has low magnetic order temperature (~70 K) and A-type AFM structure, which hinders its applications. We have synthesized $YMn1_{-x}Cr_xO_3$ (x = 0, 0.05 and 0.1) samples by the conventional solid-state reaction. The powders of stoichiometric proportions were mixed, and calcined at $900^{\circ}C$ for $YMn1_{-x}Cr_xO_3$ for 24 h. The obtained powders were ground, and pressed into 5-mm-thick disks of 1/2-inch diameter. The disks were directly put into the oven, and heated up to $1,300^{\circ}C$ and sintered in air for 24 h. The phase of samples was checked at room temperature by powder x-ray diffraction using a Rigaku Miniflex diffractometer with Cu $K{\alpha}$ radiation. All the magnetization measurements were carried out with a superconducting quantum-interference-device magnetometer. Our experiments point out that the Cr-doped samples show the characteristics of a spin-glass state at low temperatures.

• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
• /
• pp.508-508
• /
• 1996

;The growth of films have considerable interest in the field of superlattice structured multi-layer epitaxy led to realization of new devices concepts. Molecular beam epitaxy (MBE) with in situ observation by reflection high-energy electron diffraction (RHEED) is a key technology for controlled layered growth on the atomic scale in oxide crystal thin films. Also, the combination of radical oxygen source and MBE will certainly accelerate the progress of applications of oxides. In this study, the growth process of single crystal films using by MBE method is discussed taking the oxide materials of Bi-Sr-Ca-Cu family. Oxidation was provided by a flux density of activated oxygen (oxygen radicals) from an rf-excited discharge. Generation of oxygen radicals is obtained in a specially designed radical sources with different types (coil and electrode types). Molecular oxygen was introduced into a quartz tube through a variable leak valve with mass flowmeter. Corresponding to the oxygen flow rate, the pressure of the system ranged from $1{\;}{\times}{\;}10^{-6}{\;}Torr{\;}to{\;}5{\;}{\times}{\;}10^{-5}$ Torr. The base pressure was $1{\;}{\times}{\;}10^{-10}$ Torr. The growth of Bi-oxides was achieved by coevaporation of metal elements and oxygen. In this way a Bi-oxide multilayer structure was prepared on a basal-plane MgO or $SrTiO_3$ substrate. The grown films compiled using RHEED patterns during and after the growth. Futher, the exact observation of oxygen radicals with MBE is an important technology for a approach of growth conditions on stoichiometry and perfection on the atomic scale in oxide. The oxidization degree, which is determined and controlled by the number of activated oxygen when using radical sources of two types, are utilized by voltage locked loop (VLL) method. Coil type is suitable for oxygen radical source than electrode type. The relationship between the flux of oxygen radical and the rf power or oxygen partial pressure estimated. The flux of radicals increases as the rf power increases, and indicates to the frequency change having the the value of about $2{\times}10^{14}{\;}atoms{\;}{\cdots}{\;}cm^{-2}{\;}{\cdots}{\;}S^{-I}$ when the oxygen flow rate of 2.0 seem and rf power 150 W.150 W.