• Journal of the Korean Vacuum Society
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• v.16 no.2
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• pp.122-127
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• 2007

In this research, amophous carbon films (a-C, a-C:H, a-C:N) were synthesized by closed-field unbalanced magnetron (CFUBM) sputtering using graphite target. We also fabricated amorphous carbon films with applying negative DC bias voltage of 200 V in during the deposition in working pressure. Also, a-C:H and a-C:N films was synthesized by adding acethylene($C_{2}H_{2}$) and nitrogen(N) gases of 4 and 3 sccm into Ar pressure. The a-C:H film synthesized at -200 V exhibited the maxumum hardness of 26.3 GPa, the smooth surface of 0.1 nm and the good adhesion of 30.5 N. And a-C:N film synthesized at -200 V exhibited at -200 V exhibited the best adhesion of 32 N. This paper examined the effect of $C_{2}H_{2}$ gas, $N_{2}$ gas and negative DC bias voltage as the parameter for improving the physical properties and the relation between structral and physical properties of carbon films.

• Bulletin of the Korean Mathematical Society
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• v.50 no.3
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• pp.839-865
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• 2013

We deal with the existence of positive radial solutions concentrating on spheres for the following class of elliptic system $$\large(S) \hfill{400} \{\array{-{\varepsilon}^2{\Delta}u+V_1(x)u=K(x)Q_u(u,v)\;in\;\mathbb{R}^N,\\-{\varepsilon}^2{\Delta}v+V_2(x)v=K(x)Q_v(u,v)\;in\;\mathbb{R}^N,\\u,v{\in}W^{1,2}(\mathbb{R}^N),\;u,v&gt;0\;in\;\mathbb{R}^N,}$$ where ${\varepsilon}$ is a small positive parameter; $V_1$, $V_2{\in}C^0(\mathbb{R}^N,[0,{\infty}))$ and $K{\in}C^0(\mathbb{R}^N,[0,{\infty}))$ are radially symmetric potentials; Q is a $(p+1)$-homogeneous function and p is subcritical, that is, 1 < $p$ < $2^*-1$, where $2^*=2N/(N-2)$ is the critical Sobolev exponent for $N{\geq}3$.

• Progress in Superconductivity
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• v.12 no.1
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• pp.46-50
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• 2010

In the superconducting $Sr_2VO_3FeAs$, containing bimetallic layers, with maximum $T_c{\approx}\;46\;K$ correlation effects on V ions have been investigated using LDA+U method. Within the local density approximation (LDA) this system has the one-third filled $t_{2g}$ manifold of V, decomposed into $d_{xy}$ of bandwidth W=2 eV and nearly degenerate $d_{zx}d_{yz}$ of W=1 eV. Consideration of correlation effects leads to a metal-insulator transition on V ions $t^{2\uparrow}_{2g}\;{\rightarrow}\;d^{1\uparrow}_{xz}\;d^{1\uparrow}_{yz}$ at the critical on-site Coulomb repulsion $U_c$= 3.5 eV. At U=4 eV, the electronic structure, in which V ions are insulating, leads to several van Hove singularities near $E_F$ and similar Fermiology with other pnictides. Applying U to V ions results in increasing Fe moment as well as V moment, indicating somewhat hybridization between Fe and V ions even though this system is strongly 2-dimesional. Our results show possible importance of correlation effects on this system.

• Journal of the Korean Vacuum Society
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• v.5 no.3
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• pp.213-217
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• 1996

HgS and HgS: Co crystals and films grown by the slow cooling and the chemical bath deposition method were used to measure their crystal structure and their optical absorption spectra. HgS and HgS: Co crystals are hexagonal structure with the lattice constant $a_0=4.155{\AA}$, $c_0=9.505{\AA}$ for HgS and $a_0=4.148{\AA}$, $c_0=9.462{\AA}$ for HgS and $a_0=4.135{\AA}$, $c_0=9.442{\AA}$ for HgS: Co, respectively. The optical energy gap of these crystals are given as 2.040 eV for HgS and 1.900 eV for HgS: Co, and the optical energy gap of these films were 2.440 eV for HgS and 1.940 eV for HgS: Co at room temperature, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.351-356
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• 1995

A optical switch which on the LiNbO$_3$substrate is fabricated by using proton exchange method and self-alignet method. The annealing at 400[$^{\circ}C$] was carried out to control waveguide width and depth. A self-aligned method, which doesn\`t need the additional mask precesses, was applied to simplify the fabrication processes and to maximize efficiency of electric field application. The depths of the two annealed optical waveguides, which were measured by using ${\alpha}$-step, ware 1.435[K${\AA}$] and 1,380[K${\AA}$]. Using ${\alpha}$-step facility, we examined that the width of waveguides is increased from 5[$\mu\textrm{m}$] to 6.45[$\mu\textrm{m}$] and 6.3[$\mu\textrm{m}$] due to the annealing effects. The process of proton exchange was done at 400[$^{\circ}C$] for 60[min] and annealing process was done at 400[$^{\circ}C$] for 60[min]. The high speed optical modulator has very good figures of merits: the measured voltage of the input waveguide power is 3.5[V], the voltage of the coupling waveguide power is 3.9[mV], and -29.5[dB] crosstalk and 8[V] switching voltage were achieved.

• Structural Engineering and Mechanics
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• v.20 no.3
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• pp.293-312
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• 2005

In this paper, free vibration of rotating beam with random properties is studied. The cross-sectional area, elasticity modulus, moment of inertia, shear modulus and density are modeled as random fields and the rotational speed as a random variable. To study uncertainty, stochastic finite element method based on second order perturbation method is applied. To discretize random fields, the three methods of midpoint, interpolation and local average are applied and compared. The effects of rotational speed, setting angle, random property variances, discretization scheme, number of elements, correlation of random fields, correlation function form and correlation length on "Coefficient of Variation" (C.O.V.) of first mode eigenvalue are investigated completely. To determine the significant random properties on the variation of first mode eigenvalue the sensitivity analysis is performed. The results are studied for both Timoshenko and Bernoulli-Euler rotating beam. It is shown that the C.O.V. of first mode eigenvalue of Timoshenko and Bernoulli-Euler rotating beams are approximately identical. Also, compared to uncorrelated random fields, the correlated case has larger C.O.V. value. Another important result is, where correlation length is small, the convergence rate is lower and more number of elements are necessary for convergence of final response.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.94-98
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• 2000

Polycrystalline SBTN ferroelectric thin films were prepared by sol-gel method with various Nb mole ratios on Pt/ $SiO_2$/Si (100) substrates. The films were annealed at different temperatures and characterized in terms of phase and microstructure. Relatively a well saturated hysteresis pattern was obtained at x =0.2 in S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin films. At an applied voltage of 5V, the dielectric constant ($\varepsilon$$_{r}$) and dissipation factor (tan $\delta$) of typical S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin film (x=0.2) were about 236.2 and 0.034. Measured remanent polarization (2Pr) and coercive field (Ec) were 4.28C/c $m_2$, and 38.88kv/cm respectively. No fatigue was observed up to 6$\times$10$_{10}$ switching cycles at 5V and the normalized polarization reduced by a factor of only 4%.%. 4%.%. 4%.%.%.%.%.

• Bulletin of the Korean Chemical Society
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• v.21 no.10
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• pp.953-954
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• 2000

The equilibrium geometrical structures of silver atom clusters at their electronic ground states have been theo-retically determined by using the nonrelativistic semiempirical INDO/1 method. The clusters investigated are Agn, Agn+, and Agn- (n = 7 , 8, 9). In order to find the most stable structure, i.e., the global minimum in energy hypersurface, geometry optimization and energy calculation processes have been repeatedly performed for all the possible graphical models by changing the bond parameters (resonance integral values). The heptamers are pentagonal bipyramidal-Ag7(D5h), Ag7+ (D5h), Ag7- (D5h); the octamers are pentagonal bipyramidal with one atom capped-Ag8(D2d), Ag8+ (Cs), Ag8- (D2d); the nonamers are pentagonal bipyramidal with two atoms capped -Ag9(C2v), Ag9+ (C2v), Ag9- (C2v). Our structures are in good agreement with those by ab initio calculations ex-cept for the anionic Ag9- cluster. And it is noted that the INDO/1 method can accurately predict the Ag cluster geometries when a proper set of bond parameters is used.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.12
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• pp.59-64
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• 1991

Thin (25-103$\AA$) SiO$_2$ films are grown using the rapid thermal oxidation processing at temperatures of 105$0^{\circ}C$-115$0^{\circ}C$ for 5-30 sec, in order to investigate the characteristics of ultra thin oxide. For measuring the thickness of oxide TEM, ellipsometry, and C-V method which is taken in the condition of small surface band bending are used and compared. When neglecting the small deviation affected by both interface state and moisture charge effect, those three methods described above give similar results. In order to examine the effect of rapid thermal annealing, part of samples are annealed in N$_2$ ambient. MOS capacitors are fabricated and the characteristics of I-V and C-V are measured. Measurements show that the activation energy of initial thickness of oxide grown during the ramp-up time is of 1.125eV and the activation energy of the oxidation rate is of 0.98eV. As oxidation temperature is increased, dielectric breakdown field E$_{BD}$ is decreased due to the increase of fixed charge density N$_f$ However, E$_{BD}$ is shown to be decreased as increasing the thickness of oxide. The increase of N$_f$ in the early stage of thermal annealing results in the decrease of E$_{BD}$.

• Communications of the Korean Mathematical Society
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• v.27 no.3
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• pp.557-564
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• 2012

This study concerns the existence of positive solution for the following nonlinear system $$\{-div(|x|^{-ap}|{\nabla}u|^{p-2}{\nabla}u)=|x|^{-(a+1)p+c_1}({\alpha}_1f(v)+{\beta}_1h(u)),x{\in}{\Omega},\\-div(|x|^{-bq}|{\nabla}v|q^{-2}{\nabla}v)=|x|^{-(b+1)q+c_2}({\alpha}_2g(u)+{\beta}_2k(v)),x{\in}{\Omega},\\u=v=0,x{\in}{\partial}{\Omega}$$, where ${\Omega}$ is a bounded smooth domain of $\mathbb{R}^N$ with $0{\in}{\Omega}$, 1 < $p,q$ < N, $0{{\leq}}a<\frac{N-p}{p}$, $0{{\leq}}b<\frac{N-q}{q}$ and $c_1$, $c_2$, ${\alpha}_1$, ${\alpha}_2$, ${\beta}_1$, ${\beta}_2$ are positive parameters. Here $f,g,h,k$ : $[0,{\infty}){\rightarrow}[0,{\infty})$ are nondecresing continuous functions and $$\lim_{s{\rightarrow}{\infty}}\frac{f(Ag(s)^{\frac{1}{q-1}})}{s^{p-1}}=0$$ for every A > 0. We discuss the existence of positive solution when $f,g,h$ and $k$ satisfy certain additional conditions. We use the method of sub-super solutions to establish our results.