• The Journal of Engineering Geology
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• v.9 no.3
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• pp.187-206
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• 1999

A computer program to numerically predict the permeability tensor of fractured rocks is developed using information on discontinuities which Borehole Televiewer and Borehole Image Processing System (BIPS) provide. It uses orientation and thickness of a large number of discontinuities as input data, and calculates relative values of the 9 elements consisting of the permeability tensor by the formulation based on the EPM model, which regards a fractured rock as a homogeneous, anisotropic porous medium. In order to assess feasibility of the program on field sites, the numerically calculated tensor was obtained using BIPS logs and compared to the results of pumping test conducted in the boreholes of the study area. The degree of horizontal anisotropy and the direction of maximum horizontal permeability are 2.8 and $N77^{\circ}CE$, respectively, determined from the pumping test data, while 3.0 and $N63^{\circ}CE$ from the numerical analysis by the developed program. Disagreement between two analyses, especially for the principal direction of anisotropy, seems to be caused by problems in analyzing the pumping test data, in applicability of the EPM model and the cubic law, and in simplified relationship between the crack size and aperture. Aside from these problems, consideration of hydraulic parameters characterizing roughness of cracks and infilling materials seems to be required to improve feasibility of the proposed program. Three-dimensional assessment of its feasibility on field sites can be accomplished by conducting a series of cross-hole packer tests consisting of an injecting well and a monitoring well at close distance.

• Korean Journal of Materials Research
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• v.13 no.7
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• pp.447-452
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• 2003

Effects of annealing and thickness of Co layer in Co/IrMn bilayers on the magnetic properties have been investigated. The highest interfacial exchange coupling energy($J_{K}$ = 0.12 erg/$\textrm{cm}^2$) was obtained for 10 nm Co layer thickness. Exchange bias field is inversely proportional to the magnetization, the thickness of the pinned layer, and the grain size of antiferromagnetic layer. Also it is related to the interfacial exchange energy difference, which is expected to depend on the surface roughness. These results almost agree with the random-field model of exchange anisotropy proposed by Malozemoff. Exchange bias field decreased slowly with increasing annealing temperature up to X$300^{\circ}C$. However, exchange bias field increased above $300^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.744-751
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• 2003

Co-Pd alloy thin films prepared by a DC-sputter that have self-organized nano structure(SONS), are promising for high-density information storage media in information era. We prepared the samples by varying Pd contents of 0~8.1 wt% at the substrate temperatures of room temperature (RT) and 200 $^{\circ}C$, respectively Microstructure and Pd contents of the Co$_{1-x}$ Pd$_{x}$ films are probed by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an energy dispersive spectrometer (EDS). We also investigated the saturation magnetization (Ms), remanence and coercivity of the Co$_{1-x}$ Pd$_{x}$ films. Surface roughness are measured by an atomic force microscope (AFM). We revealed that self-organized nano size Co-enriched phase and Pd-enriched phase existed with Pd contents at the substrate temperatures of RT and 20$0^{\circ}C$ through microstructure characterization. SONS helped to keep the saturation magnetization and enhance the perpendicular anisotropy with Pd contents. Out result implies that we may tune the perpendicular magnetic properties with keeping the saturation magnetization by varying substrate temperatures and Pd contents for high density magnetic recording.rding.

• Korean Journal of Materials Research
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• v.26 no.4
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• pp.207-211
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• 2016

Ti films were deposited on glass substrates under various preparation conditions in a chamber of two-facing-target type dc sputtering; after deposition, the electric resistivity values were measured using a conventional four-probe method. Crystallographic orientations and microstructures, including the texture and columnar structure, were also investigated for the Ti films. The morphological features, including the columnar structures and surface roughness, are well explained on the basis of Thornton's zone model. The electric resistivity and the thermal coefficient of the resistivity vary with the sputtering gas pressure. The minimum value of resistivity was around 0.4 Pa for both the $0.5{\mu}m$ and $3.0{\mu}m$ thick films; the apparent tendencies are almost the same for the two films, with a small difference in resistivity because of the different film thicknesses. The films deposited at high gas pressures show higher resistivities. The maximum of TCR is also around 0.4 Pa, which is the same as that obtained from the relationship between the resistivity and the gas pressure. The lattice spacing also decreases with increasing sputtering gas pressure for both the $0.5{\mu}m$ and $3.0{\mu}m$ thick films. Because they are strongly related to the sputtering gas pressures for Ti films that have a crystallographic anisotropy that is different from cubic symmetry, these changes are well explained on the basis of the film microstructures. It is shown that resistivity measurement can serve as a promising monitor for microstructures in sputtered Ti films.

• Journal of the Korean Magnetics Society
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• v.6 no.4
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• pp.235-241
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• 1996

Co/Pd and Co/Pt multilayered thin films for perpendicular magnetic recording media were fabricated by sput¬tering method and the effects of the sputtering pressure during the formation of Pd or Pt underlayers on the magnetization behavior and coercivity of the multilayers were investigated. It was found that the coercivity of Co/Pd multilayers was strongly dependent on the sputtering pressure of underlayer and could be enhanced to a large extent merely by increasing the sputtering pressure of underlayer, while in case of Co/Pt films, the degree of coercivity enhancement by controlling the sputtering pressure of underlayer was almost negligible. Coercivity variation of Co/Pd and Co/Pt multilayers with the underlayer material and deposition pressure of underlayer could be well explained in terms of the interface roughness of multilayer films induced by underlayer topology, which could also be correlated to the change of perpendicular anisotropy energy and magnetic reversal feature with the sputtering pressure of underlayer. Kerr rotation angle was hardly affected by the preparation conditions of underlayers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12S
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• pp.1187-1194
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• 2003

A BCl$_3$/Ne plasma chemistry was used to etch Ga-based (GaAs, AIGaAs, GaSb) and In-based (InGaP, InP, InAs and InGaAsP) compound semiconductors in a Planar Inductively Coupled Plasma (ICP) reactor. The addition of the Ne instead of Ar can minimize electrical and optical damage during dry etching of III-V semiconductors due to its light mass compared to that of Ar All of the materials exhibited a maximum etch rate at BCl$_3$ to Ne ratios of 0.25-0.5. Under all conditions, the Ga-based materials etched at significantly higher rates than the In-based materials, due to relatively high volatilities of their trichloride etch products (boiling point CaCl$_3$ : 201 $^{\circ}C$, AsCl$_3$ : 130 $^{\circ}C$, PCl$_3$: 76 $^{\circ}C$) compared to InCl$_3$ (boiling point : 600 $^{\circ}C$). We obtained low root-mean-square(RMS) roughness of the etched sulfate of both AIGaAs and GaAs, which is quite comparable to the unetched control samples. Excellent etch anisotropy ( > 85$^{\circ}$) of the GaAs and AIGaAs in our PICP BCl$_3$/Ne etching relies on some degree of sidewall passivation by redeposition of etch products and photoresist from the mask. However, the surfaces of In-based materials are somewhat degraded during the BCl$_3$/Ne etching due to the low volatility of InCl$_{x}$./.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.486-492
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• 1999

The purpose of this research was to find out what is the dominant factor determining the $H_{ex}$ and the $H_C$ of Mn-Ir/Ni-Fe multilayers with different buffer layers. Regardless of (111) texture of Mn-Ir layer, all samples showed over the $H_{ex}$ of 155 Oe. We found out the $H_{ex}$ and the $H_C$ of Mn-Ir/Ni-Fe multilayers depend on interface morphology and grain size of Mn-Ir layer at the interface between Mn-Ir and Ni-Fe layers. The dependence of magnetroesistance ratio and coupling field on the thickness of ferromagnetic layer, thickness of Cu layer and different buffer layers have been studied. Maximum magnetoresistance ratio appeared for the sample Ta(5 nm)/Mn-Ir(10 nm)/Ni-Fe(7.5 nm)/Cu(2 nm)/Ni-Fe(6 nm)/Ta(5 nm)/Si. Magnetoresistance ratio may be related to grain of ferromagnetic layer. Coupling field may be related to the roughness and the grain size of ferromagnetic layer in the spin-valve multilayers.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.125-125
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• 2010

극성 [0001] 방향으로 성장된 질화물 기반의 LED (light emitting diode) 는 분극현상에 의해 발생하는 강한 내부 전기장의 영향을 받게 된다. 이러한 내부 전기장은 양자우물 내의 전자와 정공의 공간적 분리를 야기하고 quantum confined Stark effect (QCSE)에 의한 발광 파장의 적색 편이가 발생하며 양자효율의 저하를 가져오게 된다. 이러한 문제를 해결하기 위해 InGaN/GaN이나 AlGaN/GaN 양자 우물구조를 GaN의 m-plane (1$\bar{1}$00) 이나 a-plane (11$\bar{2}$0) 등 비극성면 위에 성장하려는 시도를 하고 있다. 그러나 비극성 면의 비등방성 (anisotropy) 으로 인하여 결정성이 높은 비극성 GaN을 성장하는 데에는 많은 어려움이 있다. GaN 층의 표면을 평탄화하고 결정성을 향상시키기 위해서 저온 GaN 또는 AlN 버퍼층을 성장하는 2단계 방법이나 고온 버퍼층을 이용하여 성장하는 연구들이 많이 진행되고 있다. 본 연구에서는 고온 GaN 버퍼층을 이용하여 기존의 2단계 성장과정을 단순화한 비극성 a-plane GaN을 r-plane 사파이어 기판위에 유기금속 화학증착법 (MOCVD)으로 성장하였다. 사파이어 기판위에 AlN 층을 형성하기 위한 nitridation 과정 후 1030 도에서 두께 45 ~ 800 nm의 고온 GaN 버퍼층을 성장하고 총 박막 두께가 2.7 ~ 3 um 가 되도록 a-plane GaN을 성장하여 표면 양상의 변화와 결정성을 확인하였다. 또한 a-plane GaN 박막 성장 시에 성장 압력을 100 ~ 300 torr 로 조절하며 박막 성장의 변화 양상을 관찰하였다. 고온 GaN 버퍼층 성장 두께가 감소함에 따라 결정성은 증가하였으나 표면의 삼각형 형태의 pit 밀도가 증가함을 확인하였다. 또한 성장 압력이 감소함에 따라 표면 pit은 감소하였으나 결정성도 감소하는 것을 확인하였다. 성장 압력과 버퍼층 성장 두께를 조절하여 표면에 삼각형 형태의 pit이 존재하지 않는 RMS roughness 0.99 nm, 관통전위밀도 $1.78\;{\times}\;10^{10}/cm^2$, XRD 반가폭이 [0001], [1$\bar{1}$00] 방향으로 각 798, 1909 arcsec 인 a-plane GaN을 성장하였다. 이 연구를 통해 고온 GaN 버퍼 성장방법을 이용하여 간소화된 공정으로 LED 소자 제작에 사용할 수 있는 결정성 높은 a-plane GaN을 성장할 수 있는 가능성을 확인하였다.