• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.320-325
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• 2023

In Li-ion batteries, a thick electrode is advantageous for lowering the inactive current collector portion and obtaining a high energy density. One of the critical failure mechanisms of thick electrodes is inhomogeneous lithiation and delithiation owing to the axial location of the electrode. In this study, it was confirmed that the top layer of the composite electrode contributes more to the charging step owing to the high ionic transport from the electrolyte. A high-loading multilayered electrode containing LiFePO₄ (LFP) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) was developed to overcome the inhomogeneous electrochemical reactions in the electrode. The electrode laminated with LFP on the top and NCM811 on the bottom showed superior cyclability compared to the electrode having the reverse stacking order or thoroughly mixed. This improvement is attributed to the structural and interfacial stability of LFP on top of the thick electrode in an electrochemically harsh environment.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.261-264
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• 2014

$SrTiO_3$ (STO) single crystal irradiated with a 3-MeV proton beam exhibits blue and green mixed luminescence. However, the same proton beam when used to irradiate STO with a very thin layer of deposited Pt does not show any luminescence. This Pt layer prevents any damage which may otherwise be caused by arcing, which stems from the accumulated surface voltage of tens of kV due to the charge induced by secondary electrons on the surface of the insulator during the ion beam irradiation process. Hence, the luminescence of ion-irradiated STO originates from the modification of the STO surface layer caused by arcing rather than from any direct ion beam irradiation effect. STO treated with atmospheric-pressure plasma, a simple and cost-effective method, also exhibits the same type of blue and green mixed luminescence as STO treated with an ion beam, as the plasma also creates a layer of surface damage due to arcing.

• 중소기업융합학회논문지
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• 제6권3호
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• pp.49-55
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• 2016

본 논문에서는 다양한 채널 환경과 요구 화질 조건에서 사용자의 QoS(Quality of Service)를 만족시키기 위한 영상 전송 방법에 대하여 제안하였다. SVC(Scalable Video Coding) 전송 기법은 비디오 신호를 중요도를 고려한 계층별 신호로 인코딩하여 전송하기 때문에, 비디오 신호 전송에 있어 효과적인 방법이다. 하지만 다양한 채널 환경에 대해서 적응적으로 다수의 사용자가 요구하는 각각의 성능을 선택적으로 만족시키는 기술에 대한 연구는 미비하다. 이에 본 논문에서는 MC-CDMA기반의 SVC 전송 시스템에서 계층 간 차등 OVSF(Orthogonal Variable Spreading Factor) 코드 할당 기법을 통해 SVC 계층 간 protection order를 보장하고 수신부로부터의 피드백을 통해 MC-CDMA의 sub-block과 각각의 계층 신호에 할당된 OVSF 길이를 조절하여 전송함으로써 다양한 채널 환경에서 각각의 사용자의 전송 환경에 따른 최적의 영상품질을 제공하는 적응 전송 시스템을 제안한다. 모의실험을 통해 제안 시스템의 성능분석을 실시한 결과 BER 성능이 향상되어 사용자의 QoS 만족이 가능함을 확인할 수 있었다.

• 반도체디스플레이기술학회지
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• 제20권4호
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• pp.16-22
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• 2021

We search for an appropriate initial adsorption coordination of precursor on surface by using genetic algorithm (GA) and density functional theory. SiH₄ and Al(CH₃)₃ as precursor, and OH-terminated Si (001) as surface are used for this study. Selection, crossover, and mutation as hyperparameters of GA are applied to search for the adsorption coordination of the precursors on the surface as a function of generation. Bond distances between precursors and the surface are used to explain the adsorption behavior of the precursors.

• Applied Science and Convergence Technology
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• 제25권4호
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• pp.73-76
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• 2016

Multi-layer films of $SiN_x/SiO_x$/InSnO with anti-reflective effect were grown by new-concept plasma enhanced chemical vapor deposition system (PECVD) with hybrid plasma source (HPS). Anti-reflective effect of $SiN_x/SiO_x$/InSnO was investigated as a function of ratio of $SiN_x$ and $SiO_x$ thickness. Multi-layers deposited by PECVD with HPS represents the enhancement of anti-reflective effect with high transmittance, comparing to the layers by conventional radio frequency (RF) sputtering system. This change is strongly related to the optical and physical properties of each layer, such as refractive index, composition, film density, and surface roughness depending on the deposition system.

• 한국세라믹학회지
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• 제53권3호
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• pp.282-287
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• 2016

This study involves enhancing the performance of the $Na(Li,Ti)O_2$ system as an Na-ion battery anode with the addition of Mg, which partially replaces Li ions. We perform both computational and experimental approaches to achieve a higher reversible capacity and a faster transport of Na ions for the devised system. Computational results indicate that the $Na(Li,Mg,Ti)O_2$ system can provide a lower-barrier path for Na-ion diffusion than can a system without the addition of Mg. Experimentally, we synthesize various $Na_z(Li_y,Mg_x,Ti)O_2$ systems and evaluate their electrochemical characteristics. In agreement with the theoretical study, Mg addition to such systems improves general cell performance. For example, the prepared $Na_{0.646}(Li_{0.207}Mg_{0.013}Ti_{0.78})O_2$ system displays an increase in reversible capacity of 8.5% and in rate performance of 13.5%, compared to those characteristics of a system without the addition of Mg. Computational results indicate that these improvements can be attributed to the slight widening of the Na-$O_6$ layer in the presence of Mg in the $(Li,Ti)O_6$ layer.

• 한국재료학회지
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• 제24권11호
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• pp.573-577
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• 2014

The existing metal getters are invariably covered with thin oxide layers in air and the native oxide layer must be dissolved into the getter materials for activation. However, high temperature is needed for the activation, which leads to unavoidable deleterious effects on the devices. Therefore, to improve the device efficiency and gas-adsorption properties of the device, it is essential to synthesize the getter with a method that does not require a thermal activation temperature. In this study, getter material was synthesized using palladium oxide (PdOx) which can adsorb $H_2$ gas. To enhance the efficiency of the hydrogen and moisture absorption, a porous layer with a large specific area was fabricated by an etching process and used as supporting substrates. It was confirmed that the moisture-absorption performance of the $SiO_2/Si$ was characterized by water vapor volume with relative humidity. The gas-adsorption properties occurred in the absence of the activation process.

• Carbon letters
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• 제14권4호
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• pp.228-233
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• 2013

In this work, we report in-situ observations of changes in catalyst morphology, and of growth termination of individual carbon nanotubes (CNTs), by complete loss of the catalyst particle attached to it. The observations strongly support the growth-termination mechanism of CNT forests or carpets by dynamic morphological evolution of catalyst particles induced by Ostwald ripening, and sub-surface diffusion. We show that in the tip-growth mode, as well as in the base-growth mode, the growth termination of CNT by dissolution of catalyst particles is plausible. This may allow the growth termination mechanism by evolution of catalyst morphology to be applicable to not only CNT forest growth, but also to other growth methods (for example, floating-catalyst chemical vapor deposition), which do not use any supporting layer or substrate beneath a catalyst layer.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.301-307
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• 2014

We have fabricated $SnO_2$/Zn core-shell nanowires by employing a sputtering technique with a Zn target. Scanning electron microscopy indicated that the surface of the nanowires became rougher by the coating. X-ray diffraction of the coated nanowires exhibited the hexagonal Zn diffraction peaks. TEM image of coated structures showed that shell layer was mainly comprised of hexagonal Zn phase. EDX spectra suggested that the shell layer consisted of Zn elements. The photoluminescence spectrum of the coated nanowires in conjunction with Gaussian fitting analysis revealed that the emission was disconvoluted with three Gaussian functions, which are centered at 2.1 eV in the yellow region, 2.4 eV in the green region, and 3.3 eV in the ultraviolet region. We speculated the possible mechanisms of these emission peaks.

• 한국표면공학회지
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• 제50권1호
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• pp.35-41
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• 2017

$TiO_2$, $Al_2O_3$, and $TiO_2-Al_2O_3$ nanolaminated films were grown by atomic layer deposition (ALD) on the 316L stainless steel (SS316L) substrates at a temperature of $150^{\circ}C$. The growth kinetics of $ALD-TiO_2$ and $Al_2O_3$ thin films were systematically investigated in order to precisely control the thickness of each layers in the $TiO_2-Al_2O_3$ nanolaminated films using a high-resolution transmission electron microscopy. And, the exact deposition rates of $ALD-TiO_2$ on $Al_2O_3$ surface and $ALD-Al_2O_3$ on $TiO_2$ surface were revealed to be 0.0284 nm/cycle and 0.11 nm/cycle, respectively. At given growth conditions, the microstructures of $TiO_2$, $Al_2O_3$ and $TiO_2-Al_2O_3$ nanolaminated films were amorphous. The potentiodynamic polarization test revealed that the $TiO_2-Al_2O_3$ nanolaminated film coated SS316L had a best corrosion resistance, although all ALDcoated SS316L exhibited a clear improvement of the corrosion resistance compared with a bare SS316L.