• JSTS:Journal of Semiconductor Technology and Science
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• 제7권1호
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• pp.56-65
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• 2007

This paper describes physical meanings of various influences of cavity (or pillar) shape and filling factor of dielectric material on band structures in two-dimensional photonic crystals. Influences of circular and rectangular cross-sections of cavity (or pillar) arrays on photonic band structures are considered theoretically, and significant aspects of square and triangular lattices are compared. It is shown that both averaged dielectric constant of the photonic crystal and distribution profile of photon energy play important roles in designing optical properties. For the triangular lattice, especially, it is shown that cavity array with a rectangular cross-section breaks the band structure symmetry. So, we discuss this point from the band structure and address optical properties of lattice with a circular cross-section cavity.

• Bulletin of the Korean Chemical Society
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• 제16권2호
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• pp.164-168
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• 1995

The band structure of nickel monoxide having a cation defect rock salt structure is calculated by means of the tight-binding extended Huckel method. The calculation is also made for the net charge, the DOS, the COOP, the electron density of the constituent atoms, and the O 1s binding energy shift when one of the adjacent nickel atoms is defected. It is found that the band gap near the Γ direction on the Brillouin zone is about 0.2 eV, and that all of the properties calculated including the electronic structure of the oxygen atom are more effectively affected by the surface defect than the inside one. The core O 1s binding energy shift is calculated by the use of valence potential method and the results are very satisfactory in comparison with the XPS experimental findings.

• Nano
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• 제13권12호
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• pp.1850138.1-1850138.6
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• 2018

Two-dimensional (2D) or layered materials have a great potential for applications in energy storage, catalysis, optoelectronics and gas separation. Fabricating novel 2D or quasi-2D layered materials composed of relatively abundant and inexpensive atomic species is an important issue for practical usage in industry. Here, we suggest the layer-structured AlOOH (Boehmite) as a promising candidate for such applications. Boehmite is a well-known layer-structured material and a single-layer can be exfoliated from the bulk boehmite by breaking the interlayer hydrogen bonding. We study atomic and electronic band structures of both bulk and single-layer boehmite, and also obtain the single-layer exfoliation energy using first-principles calculations.

• ETRI Journal
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• 제13권4호
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• pp.25-34
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• 1991

The stability and the electronic structure of $In_0.5$.$Ga_0.5$P-based superlattices are examined through self-consistent ab initio pseudopotential calculations. A chalcopyrite-like structure is found to be the lowest energy state over (001) and (111) monolayer superlattices (MLS). Our calculations indicate that all the ordered structures in bulk form are unstable against phase segregation into binary constituents at T = 0 while for epitaxial growth, the chalcopyrite phase is stabilized. The fundamental band gaps of the ordered structures are found to be direct and smaller than that of disordered alloys. The lowering of the band gap is explainable by band folding and pushing effects. We find the reduction of the band gap to be largest for the (111) MLS.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.267-270
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• 2004

A silver indium sulfide($AgInS_2$) epilayer was grown by the hot wall epitaxy method, which has not been reported in the literature. The grown $AgInS_2$ epilayer has found to be a chalcopyrite structure and evaluated to be high qualify crystal. From the photocurrent measurement in the temperature range from 30 K to 300 K, the two peaks of A and B were only observed, whereas the three peaks of A, B, and C were seen in the PC spectrum of 10 K. These peaks. are ascribed to the band-to-band transition. The valence band splitting of $AgInS_2$ was investigated by means of the photocurrent measurement. The crystal field splitting, $\ddot{A}cr$, and the spin orbit splitting, $\ddot{A}so$, have been obtained to be 0.150 eV and 0.009 eV at 10 K, respectively. And, the energy band gap at room temperature has been determined to be 1.868 eV. Also, the temperature dependence of the energy band gap, $E_g(T)$, was determined.

• 전기학회논문지P
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• 제66권4호
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• pp.200-205
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• 2017

In this paper, we propose a technique to determine the normal and arc of an alternating current using a mixed filter composed of an average filter and a band-pass filter and a frequency analysis. The proposed method uses the moving average filter of the FIR filter structure for noise removal and the band-pass filter of the IIR filter structure for detecting only specific frequency components after normalizing the measured current signal based on the maximum value. After performing Fast Fourier Transform (FFT) using the band-pass filtered signal, the total energy is calculated using the magnitude component of the frequency, and the arc is detected using the magnitude of the calculated energy. In order to show the validity of the proposed method, we experimented with various data and found that arc and steady state can be easily discriminated by calculating spectral energy. Therefore, it is considered that the proposed method can be applied to arc diagnosis of low voltage electric wire.

• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.349-356
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• 2011

During the process of synthesis of $TiO_2$ powders using a high-speed planetary milling machine, Fe metallic powders were created which could be dissolved in sulfuric acid solution. With adding $NH_4OH$ solution to the $TiO_2$ powder, it was found that the crystal structure of the synthesized powder did not change and the crystal size decreased slightly. However, when the sulfur powder is mixed with $TiO_2$, the crystal structure of the MA powder was changed from anatase into rutile phase and its size decreased significantly which is in the order of nm in diameter. In case of mechanical alloying with $TiO_2$ powder only, the crystal structure of the powder was transformed into rutile phase and its size was greatly reduced into several nm. Because its size becomes fine, the energy band gap of its rutile phase is larger than that of bulk states (3.0eV).

• 한국진공학회지
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• 제5권1호
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• pp.14-24
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• 1996

We have investigated atomic and electronic structures of a clean Pd(111) surface using low energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES). A typical clean LEED pattern with a 3-fold symmetry has been observed, corresponding to that for an fcc (111) surface. ARPES measurements have been performed along the $\Gamma-M,\Gamma-K,\Gamma-M$TEX> symmetry lines, from which the experimental band structure of Pd(111) has been determined. The experimental band structure and work function of Pd(111) surface are found to agree well with the calculated band structure of bulk Pd and the calculated work function of Pd(111), respectively. However, the peak positions in the experimental band structure are located closer to the Fermi level than in the theoretical band structure by 0.1~0.8 eV, depending on the $\kappa$-points in the Brillouin zone. In additin, the experimental band widths are narrower than the theoretical band widths by about 0.5eV. The effects of the localized surface Pd 4d states and the Coulomb interaction between Pd 4d bulk electrons have been discussed as possible origins of such discrepancies between experiment and theory.

• 전기화학회지
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• 제14권3호
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• pp.145-151
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• 2011

ZnSe는 가시광선 영역에서 넓은 밴드갭을 가지고 있는 II-VI족 화합물 반도체 소자로서 레이저 다이오드, 디스플레이 그리고 태양전지와 같은 다양한 응용분야에 적용되고 있다. 본 연구에서는 전기화학적 전착방법을 이용하여 ITO 전극상에 ZnSe 박막을 합성하여, XRD와 SEM으로 ZnSe 결정의 합성과 zinc blende 구조의 형태를 관측하였고, UV 분광기를 활용하여 밴드갭을 측정한 결과 2.76 eV이었다. 또한, 분자동역학에서 활용되는 밀도범함수 이론 (DFT, Density Functional Theory)을 도입하여 ZnSe 결정에 대한 밴드 구조의 해석을 수행하였다. Zinc blende구조를 갖는 ZnSe 결정에 대하여 LDA (Local Density Approximation), PBE (Perdew Burke Ernzerhof), 그리고 B3LYP (Becke, 3-parameter, Lee-Yang-Parr) 범함수를 이용하여 밴드구조와 상태밀도 (Density of State)를 모사하였다. 각각의 경우에 대해 에너지 밴드갭을 구한 결과, B3LYP 범함수로 해석한 경우에 실험치와 근사치인 2.65 eV의 밴드갭을 보여주었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.351.2-351.2
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• 2016

Graphene quantum dots (GQDs) have attracted much attention because of various advantages such as cost-effectiveness of synthesis, low toxicity, and photostability. The origins of photoluminescence (PL) in GQDs were suggested as the intrinsic states for localized sp2 carbon domains and the extrinsic states formed by oxygen-functional groups.[1,2] Nevertheless, it is still unclear to understand the information of electric band structure in GQD. Here, we observed excitation energy induced S-shaped PL behavior. The PL peak energy position shows an S-shaped shift (redshift-blueshift-redshift) as function of the excitation wavelengths. From various samples, we only observed S-shaped PL shift in the GQDs with both luminescent origins of intrinsic and extrinsic states. Therefore, this S-shaped PL shift is related to different weight of intrinsic and extrinsic states in PL spectrum depending on the excitation wavelengths. This would be the key result to understand the electric band structure of the GQDs and its derivatives.