• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.457-460
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• 2005

Nano-sized titanium oxide and zirconium oxide powders were synthesized by hydrolysis of titanium isopropoxide $[Ti(OC_3H7)_4]$ and zirconium tetrachloride ($ZrC1_4$) via a sol-gel technique. Lead titanate powders were prepared by mixing $TiO_2$ precursors with PbO slurry made with dilute $NH_4OH$. Lead zirconate titanate powders were, then, synthesized by mixing $PbTiO_3$ with $ZrO_2$ powders. The goal of this research was to obtain the $PbZrTiO_3(PZT)$ powders and sintering these powders at low temperature. The $PbTiO_3$ and PZT powders after firing were analyzed by X-ray diffraction(XRD) and transmission electron microscopy(TEM) was utilized to observe the shape and size of the synthesized nano-particles. In the XRD pattern, the well-crystallized PZT phase could be obtained in consequence of firing at $900^{\circ}C$. SEM micrographs also showed that grains of PZT were relatively well grown with the size of the range of $2{\~}4{\mu}m$. The densified perovskite structure of $PbZrTiO_3$ could be obtained by sintering at temperature as low as $900^{\circ}C$. Characterization of the samples showed improved piezoelectric properties.

• 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.

• Progress in Medical Physics
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• v.12 no.1
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• pp.1-8
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• 2001

Diamond thin films were synthesized by a chemical vapor deposition (CVD). Raman spectrum showed the diamond line at 1332 $cm^{-1}$ / and x-ray diffraction pattern exhibited a strong (111) peak of diamond. The scanning electron microscopy analysis showed that the CVD diamond thin film was grown to be unepitaxial crystallites with pyramidal hillocks. A wavelength-resolved thermoluminescence (TL) of the CVD diamond thin film irradiated with X-rays showed one peak at 430 nm around 560 K. The glow curve of the CVD diamond thin film produced one dominant 560-K peak that was caused by first-order kinetics. Its activation energy and the escape frequency were calculated to be 0.92 ～ 1.05 eV and 1.34 $\times$ 10$^{7}$ sec$^{-1}$ , respectively. The emission spectrum at 560 K was split into 1.63-eV, 2.60-eV, and 3.07-eV emission bands which is known to be attribute to silicon-vacancy center, A center, and H3 center, respectively.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.262-266
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• 2010

ZnO nanostructures were grown on an Au seed layer by a hydrothermal method. The Au seed layer was deposited by ion sputter on a Si (100) substrate, and then the ZnO nanostructures were grown with different precursor concentrations ranging from 0.01 M to 0.3M at $150^{\circ}C$ and different growth temperatures ranging from $100^{\circ}C$ to $250^{\circ}C$ with 0.3 M of precursor concentration. FE-SEM (field-emission scanning electron microscopy), XRD (X-ray diffraction), and PL (photoluminescence) were carried out to investigate the structural and optical properties of the ZnO nanostructures. The different morphologies are shown with different growth conditions by FE-SEM images. The density of the ZnO nanostructures changed significantly as the growth conditions changed. The density increased as the precursor concentration increased. The ZnO nanostructures are barely grown at $100^{\circ}C$ and the ZnO nanostructure grown at $150^{\circ}C$ has the highest density. The XRD pattern shows the ZnO (100), ZnO (002), ZnO (101) peaks, which indicated the ZnO structure has a wurtzite structure. The higher intensity and lower FWHM (full width at half maximum) of the ZnO peaks were observed at a growth temperature of $150^{\circ}C$, which indicated higher crystal quality. A near band edge emission (NBE) and a deep level emission (DLE) were observed at the PL spectra and the intensity of the DLE increased as the density of the ZnO nanostructures increased.

• Resources Recycling
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• v.18 no.4
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• pp.24-30
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• 2009

Rare earth based calcium aluminate phosphor ($CaAl_2O_4:Eu^{2+}$, $Nd^{3+}$) supported $TiO_2$ nanoparticles are synthesized by using sol-gel method, which are further characterized using powder X-ray diffraction (XRD), fourier transform infrared (FT-IR), diffuse reflectance UV-Visible spectroscopy (DRS UV-Vis) and transmission electron microscopy (TEM). The XRD pattern of as-prepared and sintered phosphor supported $TiO_2$ does not show the tendency to change the crystal structure from anatase to rutile phase up to $600^{\circ}C$. This indicates that the phosphor support might inhibit the densification and crystallite growth by providing dissimilar boundaries. The diffuse reflectance spectral (DRS) measurements showed shift towards longer wavelength indicating reduction in the band-gap energy as compared to free $TiO_2$. The FT-IR spectra of phosphor supported $TiO_2$ nanoparticles show shift in the peak positions to lower wavelengths. This indicates that the $TiO_2$ nanoparticles are not free, but covalently bonded to the phosphor support. TEM micrographs show presence of crystalline and spherical $TiO_2$ nanoparticles (8 - 15 nm diameter) dispersed uniformly on the surface of phosphor.

• Membrane Journal
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• v.23 no.2
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• pp.151-158
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• 2013

The effect of layered double hydroxides (LDH) on the gas separation properties of ethylene vinyl acetate copolymer was investigated. Mg-Al LDH/EVA nanocomposite membranes were prepared from solution intercalation using organically modified LDH (DS-LDH). Dodecyl sulfate (DS)-LDH was obtained by the intercalation of DS anion in the interlayer. The nanocomposite structure has been elucidated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). XRD pattern clearly shows that the DS-LDH layers are disorderly well dispersed in the EVA matrix. The maximum tensile strength and elongation of the LDH/EVA nanocomposite membrane were found with the LDH content 3 wt%. The thermal properties of nanocompostie membrane were enhanced by the incorporation of LDH in EVA matrix. Gas permeation of LDH/EVA nanocomposite membranes with LDH contents of 1, 3, 5 wt% was studied for $O_2$ and $CO_2$ single gases. The presence of 3 wt% LDH decreased $O_2$ permeability by up to 53% compared to the EVA membrane. In spite of barrier property of nanocomposite membrane, however, the gas permeability for $CO_2$ was increased due to its strong affinity with the residual OH groups on the LDH.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.919-925
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• 1999

Grain boundary characteristics and corrosion behavior of Alloy 600 material were investigated using the concept of grain boundary control by thermomechanical treatment(TMT). The grain boundary character distribution (GBCD) was analyzed by electron backscattered diffraction pattern. The effects of GBeD variation on intergranular at tack(JGA) and primary water stress corrosion cracking(PWSeC) were also evaluated. Changes in the fraction of coinci dence site lattice(CSL) boundaries in each cycle of TMT process were not distinguishable, but the total eSL boundary frequencies for TMT specimens increased about 10% compared with those of the commercial Alloy 600 material. It was found from IGA tests that the resistance to IGA was improved by TMT process. However, it was found from PWSCC test that repeating of TMT cycles resulted in the gradual decrease of the time to failure and the maximum load due to change in grain boundary characteristics, while the average crack propagation rate of primary crack increased mainly due to suppression of secondary crack propagation. It is considered that these corrosion characteristics in TMT specimens is attributed to 'fine tuning of grain boundary' mechanism.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.3
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• pp.49-56
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• 2002

In this study, the InGaP epilayers were grown on the exact and the $2^{\circ}$, $6^{\circ}$, $10^{\circ}$ of cut GaAs substrates by metal-organic vapor phase epitaxy, and the effects of interfacial elastic strains determined by the substrate offcut angle upon the resulting dislocation density of epilayer were investigated for the first time. The elastic strains were obtained from lattice mismatch and lattice misfit by TXRD, and the dislocation densities from epilayer x-ray FWHM. For the offcut angle range used in this study, the elastic strain was maximum and x-ray FWHM minimum at offcut angle $6^{\circ}$. From 11K PL measurements, PL wavelength was found to decrease with an increase of offcut angle. PL intensity was maximum at offcut angle $6^{\circ}$. TEM results showed that the electron diffraction pattern was of typical zincblende structure, and that the dislocation density was minimum for substrate offcut angle $6^{\circ}$. The results obtained in this study, along with the device fabrication process and beam characteristics, clearly demonstrated that the optimum substrate offcut angle for the InGaP/GaAs heterostructures is $6^{\circ}$.

• Journal of the Korean Society of Food Science and Nutrition
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• v.13 no.3
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• pp.268-274
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• 1984

The purpose of this study was to investigate the physico-chemical effects of a potato starch and a purified potato starch under the condition of the microwave heating. They were exposed to the microwave energy in a 950 W, 2,450 MHz oven for 30 through 120 seconds. As the microwave heating time was increased, the contents of moisture and the crude fat of the samples were remarkably decreased irrespective of the starch composition, but on the other hand the contents of crude ash was slightly decreased and the crude protein was almost unchanged. The rings of crystallinity come to gradually changed in the X-ray diffraction pattern, and then the only 1 ring, of which interplanner spacing is wide, is changed strikingly. As the microwave heating time is increased, the starch granules which observed by a scanning electron microscope were broken partially with a special form, and the granules of purified potato starch were broken faster than those of potato starch. With the same condition that the microwave heating time was increased, while the gelatinization temperature comes to fall, the swelling power and the solubility were increased. Besides these, while the gelatinization temperature of the purified potato starch was lower than that of the potato starch, both the swelling power and the solubility of the purified potato starch is higher than those of the potato starch.

• Journal of Powder Materials
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• v.28 no.2
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• pp.143-149
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• 2021

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x(ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.