• Journal of the Korean Magnetics Society
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• v.12 no.5
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• pp.184-188
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• 2002

The Cu/Ni/Cu(002)/Si(100) films which have perpendicular magnetic anisotropy were deposited by e-beam evaporation methods. From the reflection high energy electron diffraction pattern, the films were confirmed to be grown epitaxially on silicon. After 2X lots ions/$\textrm{cm}^2$ C+ irradiation, magnetic easy-axis was changed from surface normal to in-plane as shown in the hysteresis loop of magneto-optical Kerr effects. It became manifest from analysis of X-ray reflectivity and grazing incident X-ray diffraction that even though interface between top Cu layer and Ni layer became rougher, the contrast of Cu and Ni's electron density became manifest after ion irradiation. In addition, the strain after deposition of the films was relaxed after ion irradiation. Strain relaxation related with change of magnetic properties and mechanism of intermixed layer's formation was explained by thermo-chemical driving force due to elastic and inelastic collision of ions.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.2 no.4
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• pp.253-262
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• 2004

Construction of tunnels in a deep crystalline host rock for a potential High-Level Radioactive Waste(HLW) repository inevitably generates an excavation disturbed zone (EDZ). There have been a series of debates on whether a permeability in an EDZ increases or not and what would be the maximum depth of an EDZ. Recent studies show mixed opinions on permeability. However, there has been an international consensus on the thickness of an EDZ; 30 cm for TBM and 1 meter for controlled blast. One of the impacts of an EDZ is on determining the distance between adjacent deposition holes. The void gap by the excavation hinders relaxation of temperature profiles so that the current Korean reference designing distance between holes should be stretched out more to keep the maximum temperature in a buffer region below 100 degrees Celsius. The other impact of an EDZ is on the long-term post closure radiological safety. To estimate the impact, the reference scenario, the well scenario, is chosen. Released nuclides diffuse through a bentonite buffer region experiencing strong sorption and reach a fracture surrounded by a porous medium. Inside a fractured porous region, radionuclides migrate by advection and dispersion with matrix diffusion into a porous medium. Finally, they reach a well assumed to be a source of potable water for local residents. The annual individual dose is assessed on this well scenario to find out the significance of an EDZ. A profound sensitivity study was performed, but all results show that the impact is negligible. Even though the role of an EDZ turns out to be limited on overall safety assessment, still it is worthwhile to study the chemical role of an EDZ, such as a potential source for natural colloids, potential sealing of an open fracture by fine clay particles generated by the process of an EDZ, and alteration of a sorption mechanism by an EDZ in the future.

• Journal of the Mineralogical Society of Korea
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• v.24 no.4
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• pp.301-312
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• 2011

The study on the atomic structure of iron-bearing silicate glasses has significant geological implications for both diverse igneous processes on Earth surface and ultra-low velocity zones at the core-mantle boundary. Here, we report experimental results on the effect of iron content on the atomic structure in iron-bearing alkali silicate glasses ($Na_2O-Fe_2O_3-SiO_2$ glasses, up to 16.07 wt% $Fe_2O_3$) using $^{29}Si$ and $^{17}O$ solid-state NMR spectroscopy. $^{29}Si$ spin-lattice ($T_1$) relaxation time for the glasses decreases with increasing iron content due to an enhanced interaction between nuclear spin and unpaired electron in iron. $^{29}Si$ MAS NMR spectra for the glasses show a decrease in signal intensity and an increase in peak width with increasing iron content. However, the heterogeneous peak broa-dening in $^{29}Si$ MAS NMR spectra suggests the heterogeneous distribution of $Q^n$ species around iron in iron-bearing silicate glasses. While nonbridging oxygen ($Na-O-Si$) and bridging oxygen (Si-O-Si) peaks are partially resolved in $^{17}O$ MAS NMR spectrum for iron-free silicate glass, it is difficult to distinguish the oxygen clusters in iron-bearing silicate glass. The Lorentzian peak shape for $^{29}Si$ and $^{17}O$ MAS NMR spectra may reflect life-time broadening due to spin-electron interaction. These results demonstrate that solid-state NMR can be an effective probe of the detailed structure in iron-bearing silicate glasses.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.94.2-94.2
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• 2010

Indium tin oxide (ITO) Thin films were grown on Non-alkarai glass Substrates by PVD method and Subsequently Subjected to ($100^{\circ}C-350^{\circ}C$) Thermal Annealing (TA) In Nitr Oxygen ambinent. Most of all, The effect of TA treatment on the structural properties were studied by using X-Ray diffraction and atomic force microscopy, while optical properties were studied by UV-Transmittance measurements. After TA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, As a result, XRD peaks increase of the intensity and narrowing of full width at half-maximun (FWHM). In addtion The microstructure, The surface morphology, the optical transmittance changed and improved, and we investigated The effects of temperature, Time and atmosphere during the TA on the structural and electrical properties of the ITO/glass on TA at $300^{\circ}C$. As a results, the films are highly transparent (80%～89%) in visible region. AFM analysis shows that the films are very smooth with root mean square surface roughness 0.58nm -2.75nm thickness film. It is observed that resistivity of the films drcreases T0 $1.05{\times}10^{-4}{\Omega}cmt$ $6.06{\times}10^{-4}{\Omega}cm$, while mobility increases from $152cm^2/vs$ to $275cm^2/vs$.

• Journal of Photoscience
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• v.10 no.3
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• pp.257-261
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• 2003

We have systematically studied the evolution of the photoluminescence(PL) tuning of porous silicon(PS) by electrochemical etching in various mixed electrolytes. The electrolytes employed as an etchants were mixtures of HF:CH$_3$COOH:HNO$_3$:C$_2$H$\_$5/OH solutions where the composition ratios (%) were varied from 10:1.98:0:88.02 to 10: 1.98:8.4:79.62 under constant concentration of HF and CH$_3$COOH with a total volume of 100 ml. Changes in the surface morphology of the samples caused by variations in the etching process were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). After samples are etched in various mixed electrolytes, FTIR analyses show that there is the non-photoluminescent state and the photoluminescent state simultaneously. The PL spectra show the PL tuning in the ranging from 560 to 700 nm with the increase of HNO$_3$ concentration. An analysis of the subsequent PL relaxation mechanism was carried out by time-correlated single photon counting (TCSPC) method. Based on experimental results, it is assumed that a red shift of the main PL peak position is related to the HNO$_3$ activated formation of silicon oxygen compounds. Therefore, the use of electrolyte mixtures with composition ratios can be obtained adequate and reproducible results for PL tuning.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.160.2-160.2
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• 2014

Recently silicon has attracted intense interest as a promising anode material of lithium-ion batteries due to its extremely high capacity of 4200 mA/g (for Li4.2Si) that is much higher than 372 mAh/g (for LiC6) of graphite. However, it seriously suffers from large volume change (even up to 300%) of the electrode upon lithiation, leading to its pulverization or mechanical failure during lithiation/delithiation processes and the rapid capacity fading. To overcome this problem, Si nanowires have been considered. Use of such Si nanowires provides their facile relaxation during lithiation/delithiation without mechanical breaking. To design better Si electrodes, a study to unveil atomic-scale mechanisms involving the volume expansion and the phase transformation upon lithiation is critical. In order to investigate the lithiation mechanism in Si nanowires, we have developed a reactive force field (ReaxFF) for Si-Li systems based on density functional theory calculations. The ReaxFF method provides a highly transferable simulation method for atomistic scale simulation on chemical reactions at the nanosecond and nanometer scale. Molecular dynamics (MD) simulations with the ReaxFF reproduces well experimental anisotropic volume expansion of Si nanowires during lithiation and diffusion behaviors of lithium atoms, indicating that it would be definitely helpful to investigate lithiation mechanism of Si electrodes and then design new Si electrodes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.6
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• pp.460-464
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• 2003

The barium strontium titannate ((Ba,Sr)TiO$_3$:BST) thin films were etched in an inductively coupled plasma (ICP) as a function of CF$_4$/Ar gas mixing ratio. Under CF$_4$(20%)/Ar(80%), the maximum etch rate of the BST films was 400 $\AA$/min. Etching products were redeposited on the surface of BST and then the nature of crystallinity were varied. Therefore, we investigated the etched surface of BST by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The plasma damages were evaluated in terms of leakage current density by Agilent 4145C and dielectric constant by HP 4192 impedance analyzer. After the BST thin films exposed in the plasma, the leakage current density and roughness increases. After annealing at 600 $^{\circ}C$ for 10 min in $O_2$ ambient, the leakage current density, roughness and nonvolatile etch byproducts reduced. From this results, the plasma induced damages were recovered by annealing process owing to the relaxation of lattice mismatches by Ar ions and the desorption of metal fluorides in high temperature.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.27-32
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• 2013

We investigated the growth mechanism of amorphous-phase Si thin films in order to improve the film characteristics and circumvent photo-degradation effects by implementation of hot-wire chemical vapor deposition. Amorphous silicon thin films grown in a silane/hydrogen mixture can be decomposed by a resistive heat filament. The structural properties were observed by Raman spectroscopy, FTIR, SEM, and TEM. The electrical properties of the films were measured by photo-conductivity, dark-conductivity, and photo-sensitivity. The contents of Si-H and $Si-H_n$ bonds were measured to be 19.79 and 9.96% respectively, at a hydrogen flow rate of 5.5 sccm, respectively. The thin film has photo-sensitivity of $2.2{\times}10^5$ without a crystalline volume fraction. The catalyst behavior of the hot-wire to decompose the chemical precursors by an electron tunneling effect depends strongly on the hydrogen mixture rate and an amorphous Si thin film is formed from atomic relaxation.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.271-282
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• 2012

We explore the effect of removal of organic ligand on the atomic configurations around oxygen in hydroxyl groups in amorphous silica gel (synthesized through hydrolysis of $SiCl_4$ in diethyl-ether) using high resolution $^{17}O$ solid state NMR spectroscopy. $^1H$ and $^{29}Si$ MAS NMR spectra for amorphous silica gel showed diverse hydrogen environments including water, hydroxyl groups (e.g., hydrogen bonded silanol, isolated silanol), and organic ligands (e.g., alkyl chain) that may interact with surface hydroxyls in the amorphous silica gel, for instance, forming silica-organic ligand complex (e.g., Si-$O{\cdots}R$). These physically and chemically adsorbed organic ligands were partly removed by ultrasonic cleaning under ethanol and distilled water for 1 hour. Whereas $^{17}O$ MAS NMR spectra with short pulse length ($0.175{\mu}s$) at 9.4 T and 14.1 T for as-synthesized amorphous silica gel showed the unresolved peak for Si-O-Si and Si-OH structures, the $^{17}O$ MAS NMR spectra with long pulse length ($2{\mu}s$) showed the additional peak at ~0 ppm. The peak at ~0 ppm may be due to Si-OH structure with very fast relaxation rate as coupled to liquid water molecules or organic ligands on the surface of amorphous silica gel. The observation of the peak at ~0 ppm in $^{17}O$ MAS NMR spectra for amorphous silica gel became more significant as the organic ligands were removed. These results indicate that the organic ligands on the surface of amorphous silica gel interact with oxygen atoms in Si-OH and provide the information about atomic structure of silanol and siloxane in amorphous silica gel. The current results could enhance the understanding of dehydration mechanism of diverse silicates, which is known as atomic scale origins of intermediate depth (approximately, 70~300 km) earthquakes in subduction zone.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.237-238
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• 2006

The electrical properties such as dielectric constants and dielectric losses in the spinel samples of $LiGaTiO_4$, Li(Ga,Eu)$TiO_4$, $Li(Ga.Yb)TiO_4$ have been characterized by varying measuring temperature and frequency. The long range order structures are analyzed by rietveld refinement method. and local atomic disorder structures are analyzed by MEM (maximum entropy method). The relation between the crystal structure and dielectric properties are discussed. $LiGaTiO_4$ spinel has the IMMA with lattice constant, a = 5.86333, b=17.5872. c = 8.28375 ${\AA}$, Li-sites are partially substituted by Ga or Ti. Two crystallographic oxygen sites are partially occupied(40~50%). The dielectric constants of $LiGaTiO_4$, $LiYbTiO_4$, and $LiGa_{2/6}Eu_{1/6}Ti_{1.5}O_4$ ceramics were 127, 75 and 272, respectively at 100 kHz. The dielectric relaxation were observed in the $LiGaTiO_3$ ceramics and the temperature where dielectric loss shows maximum was $390^{\circ}C$ at 1 kHz and increased with increasing the measuring frequency.