• Bulletin of the Korean Chemical Society
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• 제27권3호
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• pp.363-367
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• 2006

The structure-property relations of ternary copper chalcogenides, $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ are examined. The density of states, band dispersions, and Fermi surfaces of these compounds are investigated to verify the reason of the metal-insulator transitions by extended Huckel tight-binding band calculations. The origin of the metalinsulator transitions of non-stoichiometric $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ is thought to be the electronic instability induced by their Fermi surface nesting.

• 한국전자파학회논문지
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• 제15권7호
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• pp.677-684
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• 2004

본 논문에서는 X밴드용 고출력 시스템에 적합한 경사진 원형 도파관 구조를 이용한 소형 T $M_{01}$-T $E_{11}$ 모드 변환기를 제안한다. 제안된 모드 변환기는 마이크로파 에너지가 RBWO 전원으로부터 혼 안테나로 효율적으로 전송되도록 파라미터 연구를 통해 최적화된 구조로 설계되었다. 그리고 반사손실, 각 모드의 전력, 임피던스 대역폭, 그리고 모드 패턴의 시뮬레이션 결과와 측정결과를 제시하였다.다.

• 한국재료학회지
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• 제19권10호
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• pp.522-526
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• 2009

Graphene has been effectively synthesized on Ni/SiO$_2$/Si substrates with CH$_4$ (1 SCCM) diluted in Ar/H$_2$(10%) (99 SCCM) by using an inductively-coupled plasma-enhanced chemical vapor deposition. Graphene was formed on the entire surface of the 500 nm thick Ni substrate even at 700 $^{\circ}C$, although CH$_4$ and Ar/H$_2$ gas were supplied under plasma of 600 W for 1 second. The Raman spectrum showed typical graphene features with D, G, and 2D peaks at 1356, 1584, and 2710 cm$^{-1}$, respectively. With increase of growth temperature to 900 $^{\circ}C$, the ratios of the D band intensity to the G band intensity and the 2D band intensity to the G band intensity were increased and decreased, respectively. The results were strongly correlated to a rougher and coarser Ni surface due to the enhanced recrystallization process at higher temperatures. In contrast, highquality graphene was synthesized at 1000 $^{\circ}C$ on smooth and large Ni grains, which were formed by decreasing Ni deposition thickness to 300 nm.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2333-2337
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• 2007

Nanoporous TiO2 and ZrO2 thin films were spin-coated using a surfactant-templated approach from Pluronic P123 (EO20PO70EO20) as the templating agent, titanium alkoxide (Ti(OC4H9)4) as the inorganic precursor, and butanol as a the solvent. The control of the electronic structure of TiO2 is crucial for its various applications. We found that the band gap of the hybrid nanoporous thin films can be easily tuned by adding an acetylacetonestabilized Zr(OC4H9)4 precursor to the precursor solution of Ti(OC4H9)4. Pores with a diameter of 5 nm-10 nm were randomly dispersed and partially connected to each other inside the films. TiO2 and ZrO2 thin films have an anatase structure and tetragonal structure, respectively, while the TiO2-ZrO2 hybrid film exhibited no crystallinity. The refractive index was significantly changed by varying the atomic ratio of titanium to zirconium. The band gap for the nanoporous TiO2 was estimated to 3.43 eV and that for the TiO2-ZrO2 hybrid film was 3.61 eV.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.378.2-378.2
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• 2014

We have investigated optical characteristics of $p-Ge_{0.99}Sn_{0.01}$ and Ge films grown on Si substrates using photoreflectance (PR) spectroscopy. The $Ge_{0.99}Sn_{0.01}$ and Ge films were grown by using an ultra-high vacuum chemical vapor deposition and molecular beam epitaxy methods, respectively. PR spectra were measured at 25 K and an extended InGaAs detector was used. By comparing $Ge_{0.99}Sn_{0.01}/Si$ and Ge/Si spectra, we observed the signals related to direct transition and split-off band of $Ge_{0.99}Sn_{0.01}$. The transition energies of $Ge_{0.99}Sn_{0.01}$ and Ge films were approximately 0.74 and 0.84 eV, respectively. Considering the shift of split-off band transition of $Ge_{0.99}Sn_{0.01}$, we suppose that the transition at 0.74 eV is attributed to direct transition between ${\Gamma}$ band and valence band. The temperature- and excitation power-dependent PR spectra were also measured.

• ETRI Journal
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• 제43권6호
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• pp.957-965
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• 2021

A miniaturized wideband band-pass filter with a 3-dB fractional bandwidth of 109.3% (1.53 GHz to 5.22 GHz), high out-of-band attenuation greater than 25 dB, and wide upper stopband up to 14 GHz is proposed. The design consists of a dual-composite right/left handed resonator, embedded open-circuited stub, and a pair of quarter-wavelength short-circuited stubs. These elements are coupled in the near distance to form a miniature filter with a compact occupied area of 0.21 λ_g×0.19 λ_g (≈ 0.013 cm²). The optimized filter has multitransmission poles in the passband, substantially improving the return loss and insertion loss characteristics. The behavior of the passband and stopband is verified against the results of a lumped element model and matrix analysis with a full-wave moment-based analysis and actual measurements. The results of this verification and a comparison with the performance of filters in other references indicate that the proposed filter is very efficient and applicable to compact microwave systems.

• 한국전기전자재료학회논문지
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• 제17권1호
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• pp.46-51
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• 2004

The cause for the variation of the initial permeability according to the Co substitution of Ni-Zn ferrite used in the LC resonance filter for the power line communication is studied. The initial permeability decreases as the quantity of Co diminishes, and the saturation magnetization increases as the quantity increases. Because the sintering density and the microstructure of ferrite show little change, the variation of the initial permeability can't be explained by the density, microstructure nor the saturation magnetization factor. The magnetocrystalline anisotropy increases, similar with the saturation magnetization, as the quantity of Co increases. The increase of magnetocrystalline anisotropy value makes the domain wall energy grow, which leads to the decrease of the initial permeability, because there's linear law between the magnetocrystalline anisotropy and the domain wall energy. The resonance frequency to Co substitution moved to high frequency band, due to the close relationship with domain wall energy, Initial permeability decreaed a little with an increase of Co contents, but resonace frequency moved to high frequency band. as a result of that, when Co was added 0.05 mol, initial permeability and resonace frequency was 75 and 25 MHz respectively.

• 분석과학
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• 제27권6호
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• pp.314-320
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• 2014

$La_{2-x}(MoO_4)_3:Er^{3+}/Yb^{3+}$ particles with doping concentrations of $Er^{3+}$ and $Yb^{3+}$ ($x=Er^{3+}+Yb^{3+}$, $Er^{3+}$=0.05, 0.1, 0.2 and $Yb^{3+}$ = 0.2, 0.45) were successfully prepared by the microwave-modified sol-gel method, and the upconversion photoluminescence properties were investigated. Well-crystallized particles, formed after heat-treatment at $900^{\circ}C$ for 16 h, showed a fine and homogeneous morphology with particle sizes of $2-5{\mu}m$. Under excitation at 980 nm, $La_{1.7}(MoO_4)_3:Er_{0.1}Yb_{0.2}$ and $La_{1.5}(MoO_4)_3:Er_{0.05}Yb_{0.45}$ particles exhibited a strong 525 nm emission band, a weak 550 nm emission band in the green region, and a very weak 655 nm emission band in the red region. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 752, 846, 922, 1358 and $1435cm^{-1}$ and lower frequency of $314cm^{-1}$ induced by the disorder of the $[MoO_4]^{2-}$ groups with the incorporation of the $Er^{3+}$ and $Yb^{3+}$ elements into the crystal lattice or by a new phase formation.

• Bulletin of the Korean Chemical Society
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• 제30권4호
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• pp.803-809
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• 2009

Notable blue shifts of the ν2 $C{\equiv}N$ stretching, $_{v4}$ C-C stretching and $_{v8}$ CCN deformation bands of $CD_3CN$ are observed upon solvation of $InCl_3$, resulting from the donor-acceptor interaction. The Raman spectrum in the $_{v2}$ region shows further details; at least two new bands emerge on the blue side of the $_{v2}$ band of free $CD_3CN$, whose relative intensities vary with concentration, suggesting that there exist at least two different cationic species in the solution. The strong hydrogen bonds formed between the methyl group and ${InCl_4}^-$ result in a large band appearing on the red side of the ν1 $CD_3$ symmetric stretching band. The solvation number of $InCl_3$, determined from the Raman intensities of the $C{\equiv}N$ stretching bands for free and coordinated $CD_3CN$, increases from $\sim$1.5 to $\sim$1.8 with decreasing concentration.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2016년도 자성 및 자성재료 국제학술대회
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• pp.34-34
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• 2016