• Journal of the Mineralogical Society of Korea
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• v.5 no.2
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• pp.72-78
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• 1992

The Earth outer core accomodates moderately considerable amount of lighter elements than pure iron itself. Hydrogen is one of the possible candidates of minor constituents in the outer core. It would be worth while to extend for the pressure effect on the solubility of hydrogen in the metal-hydrides including iron hydride. In view of hydrogen being one of the potential substitutes for petroleum, searching a more efficient way for storing hydrogen in the form of hydrides is of considerable value. For two purposes, $TiH_2$was selected among lot of hydrides for its characteristics under pressure and temperature. There have been two kinds of experiment carried out on $TiH_2$ under different experimental conditions. As one of these attempts, polycrystalline $TiH_2$ was loaded up to 15 GPa stepwise at the constant temperature 500${\circ}$ using a piston-cylinder diamond anvil cell equipped with a miniature furnace of an electric power supply. The X-ra diffraction technique was employed on the quenched samples after the simultaneous high pressure and temperature treatments. During these high pressure-temperature runs, and irreversible phase of $TiH_2$ has been observed at the pressures higher than 11.3 GPa, which would be assigned to the orthorhombic crystal system as one of the new phase(s) of $TiH_2$. Molar volume change on this phase transition is ∼10%.

• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.75-78
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• 2008

$AB_2X_4$(A, B=Transition Metal, X=O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline $[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$ compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90K. $M\"{o}ssbauer$ absorption spectra at 4.2K show that the well-developed two sextets are superposed with small difference in hyperfine fields($H_{hf}$). The hyperfine fields of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$ and $Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$ were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature($T_S=18K$) changes with Zn ions substitution below spin-reorientation temperature($T_S=28K$) of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.245-250
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• 2005

ZnO was deposited on sapphire single crystal substrate by an ultrasonic pyrolysis of Zinc Acetate Dehydrate (ZAH) with carrying Ar gas. Through Thermogravimetry-Differential Scanning Calorimetry(TG-DSC), zinc acetate dihydrate was identified to be dissolved into ZnO above $380^{\circ}C$. ZnO deposited at $380-700^{\circ}C$ showed polycrystalline structures with ZnO (101) and ZnO (002) diffraction peaks like bulk ZnO in XRD, and from which c-axis strain ${\Sigma}Z=0.2\%$ and compressive biaxial stress$\sigma=-0.907\;GPa$ was obtained for the ZnO deposited $400^{\circ}C$. Scanning electron microscope revealed that microstructures of the ZnO were dependent on the deposition temperature. ZnO grown below temperature $600^{\circ}C$ were aggregate consisting of zinc acetate and ZnO particles shaped with nanoblades. On the other hand the grain of the ZnO deposited at $700^{\circ}C$ showed a distorted hexagonal shape and was composed of many ultrafine ZnO powers of 10-25 nm in size. The formation of these ulrafine nm scale ZnO powers was explained by the model of random nucleation mechanism. The optical property of the ZnO was analyzed by the photoluminescence (PL) measurement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.16-22
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• 2008

We fabricated thermally-evaporated 10 nm-Ni/30 nm and 70 nm Poly-Si/200 nm-$SiO_2/Si$ structures to investigate the thermal stability of nickel silicides formed by rapid thermal annealing(RTA) of the temperature of $300{\sim}1100^{\circ}C$ for 40 seconds. We employed for a four-point tester, field emission scanning electron microscope(FE-SEM), transmission electron microscope(TEM), high resolution X-ray diffraction(HRIXRD), and scanning probe microscope(SPM) in order to examine the sheet resistance, in-plane microstructure, cross-sectional microstructure evolution, phase transformation, and surface roughness, respectively. The silicide on 30 nm polysilicon substrate was stable at temperature up to $900^{\circ}C$, while the one on 70 nm substrate showed the conventional $NiSi_2$ transformation temperature of $700^{\circ}C$. The HRXRD result also supported the existence of NiSi-phase up to $900^{\circ}C$ for the Ni silicide on the 30 nm polysilicon substrate. FE-SEM and TEM confirmed that 40 nm thick uniform silicide layer and island-like agglomerated silicide phase of $1{\mu}m$ pitch without residual polysilicon were formed on 30 nm polysilicon substrate at $700^{\circ}C\;and\;1000^{\circ}C$, respectively. All silicides were nonuniform and formed on top of the residual polysilicon for 70 nm polysilicon substrates. Through SPM analysis, we confirmed the surface roughness was below 17 nm, which implied the advantage on FUSI gate of CMOS process. Our results imply that we may tune the thermal stability of nickel monosilicide by reducing the height of polysilicon gate.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.399-399
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• 2013

Metal silicides는 Si 기반의microelectronic devices의 interconnect와 contact 물질 등에 사용하기 위하여 그 형성 mechanism과 전기적 특성에 대한 연구가 많이 이루어지고 있다. 이 중 Rare-earth(RE) silicides는 저온에서 silicides를 형성하고, n-type Si과 낮은 Schottky Barrier contact (~0.3 eV)을 이룬다. 또한 낮은 resistivity와 Si과의 작은 lattice mismatch, 그리고 epitaxial growth의 가능성, 높은 thermal stability 등의 장점을 갖고 있다. RE silicides 중 ytterbium silicide는 가장 낮은 electric work function을 갖고 있어 n-channel schottky barrier MOSFETs의 source/drain으로 주목받고 있다. 또한 Silicon 기반의 CMOSFETs의 성능 향상 한계로 인하여 germanium 기반의 소자에 대한 연구가 이루어져 왔다. Ge 기반 FETs 제작을 위해서는 낮은 source/drain series/contact resistances의 contact을 형성해야 한다. 본 연구에서는 저접촉 저항 contact material로서 ytterbium germanide의 가능성에 대해 고찰하고자 하였다. HRTEM과 EDS를 이용하여 ytterbium germanide의 미세구조 분석과 면저항 및 Schottky Barrier Heights 등의 전기적 특성 분석을 진행하였다. Low doped n-type Ge (100) wafer를 1%의 hydrofluoric (HF) acid solution에 세정하여 native oxide layer를 제거하고, 고진공에서 RF sputtering 법을 이용하여 ytterbium 30 nm를 먼저 증착하고, 그 위에 ytterbium의 oxidation을 방지하기 위한 capping layer로 100 nm 두께의 TiN을 증착하였다. 증착 후, rapid thermal anneal (RTA)을 이용하여 N2 분위기에서 $300{\sim}700^{\circ}C$에서 각각 1분간 열처리하여 ytterbium germanides를 형성하였다. Ytterbium germanide의 미세구조 분석은 transmission electron microscopy (JEM-2100F)을 이용하였다. 면 저항 측정을 위해 sulfuric acid와 hydrogen peroxide solution (H2SO4:H2O2=6:1)에서 strip을 진행하여 TiN과 unreacted Yb을 제거하였고, 4-point probe를 통하여 측정하였다. Yb germanides의 면저항은 열처리 온도 증가에 따라 감소하다 증가하는 경향을 보이고, $400{\sim}500^{\circ}C$에서 가장 작은 면저항을 나타내었다. HRTEM 분석 결과, deposition 과정에서 Yb과 Si의 intermixing이 일어나 amorphous layer가 존재하였고, 열처리 온도가 증가하면서 diffusion이 더 활발히 일어나 amorphous layer의 두께가 증가하였다. $350^{\circ}C$ 열처리 샘플에서 germanide/Ge interface에서 epitaxial 구조의 crystalline Yb germanide가 형성되었고, EDS 측정 및 diffraction pattern을 통하여 안정상인 YbGe2-X phase임을 확인하였다. 이러한 epitaxial growth는 면저항의 감소를 가져왔으며, 열처리 온도가 증가하면서 epitaxial layer가 증가하다가 고온에서 polycrystalline 구조의 Yb germanide가 형성되어 면저항의 증가를 가져왔다. Schottky Barrier Heights 측정 결과 또한 면저항 경향과 동일하게 열처리 증가에 따라 감소하다가 고온에서 다시 증가하였다.

• Journal of Conservation Science
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• v.34 no.3
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• pp.179-193
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• 2018

This study is aimed to investigate the provenance of raw materials and firing temperature of jar coffins excavated from the Oryang-dong kiln site and Jeonchon tomb site, Naju, Korea. Most of jar coffin samples shows same range of magnetic susceptibility and have gray color, while 404 and 405 of Jeongchon site are reddish yellow. In some samples fired at high temperature, the water absorption at the mouth rim and body part of same jar coffin were 3.50% and 7.56% respectively. It means that heat transfer and equilibrium in the kiln was not properly continued and the heat energy transferred to the mouth rim and the body part was different. In the petrographic analysis, As a tempering materials, biotite, weathered quartz and feldspar were added in the jar coffins of Oryang-dong site, and biotite, polycrystalline quartz and feldspar in it of Jeongchon site. Tempering materials were found more in the body than in the mouth rim of same jar coffin of Oryang-dong site. It seemed that some samples were fired at over 1,000 to $1,100^{\circ}C$, which showed vitrified texture in the scanning electron images and the rest of samples were fired at below $900^{\circ}C$. Due to similarity of chemical compositions, it is estimated that jar coffins of Jeongchon tomb were produced and supplied from Oryang-dong kiln site. However, the slight difference of some trace elements distribution of samples is attributed to the selection of clay depending on the location.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.11
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• pp.2573-2584
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• 1997

In this paper, Ca, Sn substitute YIC(Yttrium Iron Garnet) ceramics were fabricated with Al substitutions in Fe sites. The strip-line circulator was designed and the properties of fabricated ciculator were measured. When the electric, magnetic and microwave properties were measured in Ca, Sn substituted YIG with Al subsititions, the relative permittivity and perfmeability in microwave frequencies were 15.623 and 0.972, repectively. For $Y_{2.4}Ca_{0.3}Sn_{0.3}Fe_{5-x}Al_xO_{12}$ garnet ceramics sintered at $1450^{\circ}C$, the ferrimagnetic resonance line width $\Delta{H}$) of 42 Oe and the saturation magnetization of 487 G were measured at 10 GHz. The strip-line circulator was simulated with 3-D FEM(Finite Element Method) software and designed to have insertion loss of 0.8dB, return loss of 25dB, isolation of 35dB at the center frequency of 1.9GHz. The fabricated strition loss of 0.8B, reture loss of 25dB, isolation of 35dB at the center frequency of 1.9GHz. The fabricated strip-line junction circulator using above YIG ceramics had insertion loss of 0.869dB, return loss of 26.955dB, isolation of 44.409dB at the center frequency of 1.9GHz.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.216-219
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• 2011

Perovskite manganites such as $RE_{1-x}A_xMnO_3$ (RE = rare earth, A = Ca, Sr, Ba) have been the subject of intense research in the last few years, ever since the discovery that these systems demonstrate colossal magnetoresistance (CMR). The CMR is usually explained with the double-exchange (DE) mechanism, and CMR materials have potential applications for magnetic switching, recording devices, and more. However, the intrinsic CMR effect is usually found under the conditions of a magnetic field of several Teslas and a narrow temperature range near the Curie temperature ($T_c$). This magnetic field and temperature range make practical applications impossible. Recently, another type of MR, called the low-field magnetoresistance(LFMR), has also been a research focus. This MR is typically found in polycrystalline half-metallic ferromagnets, and is associated with the spin-dependent charge transport across grain boundaries. Composites with compositions $La_{0.7}(Ca_{1-x}Sr_x)_{0.3}MnO_3)]_{0.99}/(BaTiO_3)_{0.01}$ $[(LCSMO)_{0.99}/(BTO)_{0.01}]$were prepared with different Sr doping levels x by a standard ceramic technique, and their electrical transport and magnetoresistance (MR) properties were investigated. The structure and morphology of the composites were studied by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). BTO peaks could not be found in the XRD pattern because the amount of BTO in the composites was too small. As the content of x decreased, the crystal structure changed from orthorhombic to rhombohedral. This change can be explained by the fact that the crystal structure of pure LCMO is orthorhombic and the crystal structure of pure LSMO is rhombohedral. The SEM results indicate that LCSMO and BTO coexist in the composites and BTO mostly segregates at the grain boundaries of LCSMO, which are in accordance with the results of the magnetic measurements. The resistivity of all the composites was measured in the range of 90-400K at 0T, 0.5T magnetic field. The result indicates that the MR of the composites increases systematically as the Ca concentration increases, although the transition temperature $T_c$ shifts to a lower range.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.14-19
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• 2013

We have successfully synthesized $Bi_{4-x}La_xTi_3O_{12}$ (x~2) having Aurivillius-type layered perovskite structure from exfoliated layered perovskite oxide of $K_2La_2Ti_3O_{10}$ with Ruddlesden-Popper structure. The reaction between the exfoliated lanthanum titanate nanosheets and BiOCl nanocrystal resulted in the formation of polycrystalline $Bi_{4-x}La_xTi_3O_{12}$ (x~2) after heating above $700^{\circ}C$. Colloidal suspension of the nanosheets could be obtained by intercalating ethylamine (EA) into the protonated lanthanum titanate, $H_2La_2Ti_3O_{10}$, derived from $K_2La_2Ti_3O_{10}$. Transmission electron microscopic (TEM) analysis show that the exfoliated lanthanium titanate nanosheets have a thickness of a few nano meters. According to X-ray diffraction (XRD) analysis, the exfoliated lanthanium titanate was found to be transformed into $Bi_{4-x}La_xTi_3O_{12}$ (x~2) after restacking with BiOCl and subsequent thermal treatment at > $700^{\circ}C$.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.17-25
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• 1999

Tungsten nitride($WN_x$) films were deposited by PECVD method on silicon nitride($WSi_3N_4$) substrate. The characteristics of $WN_x$ film were investigated with changing various processing parameters ; substrate temperature, gas flow rate, rf power, and different nitrogen sources. The nitrogen composition in $WN_x$ film varied from 0 to 45% according to the $NH_3$ and $N_2$ flow rate. The highest deposition rate of 160 nm/min was obtained for the $NH_3$ gas and relatively low deposition rate of $WN_x$ films were formed by $N_2$ gas. $WN_x$ films deposited on $WSi_3N_4$ substrate had higher deposition rate than that of TiN and Si substrates. The purity of $WN_x$ film were analyzed by AES and higher purity $WN_x$ films were deposited using $NH_3$ gas. The XRD analysis indicates a phase transition from polycrystalline tungsten(W) to amorphous tungsten nitride($WN_x$), showing improved etching profile of $WN_x$ films Thick $WN_x$ films were deposited on various substrates such as Tin, NiCr and Al and maximum thickness of $1.6 {\mu}m$ was obtained on the Al adhesion layer.