• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.171.2-171.2
• /
• 2016

The 2-dimensiona electron gas (2DEG) layers have opened tremendous interests in the heterooxide interfaces formed between two insulating materials, especially between LaAlO3 and $SrTiO_3$. The 2DEG layers exhibit extremely high mobility and carrier concentrations along with metallic transport phenomena unlike the constituent oxide materials, i.e., $LaAlO_3$ and $SrTiO_3$. The current work inserted artificially the interfacial layer, $Sr_xCa_{1-x}TiO_3$ between $LaAlO_3$ and $SrTiO_3$, with the aim to controlling the 2-dimensional transports. The insertion of the additional materials affect significantly their corresponding electrical transports. Such features have been probed using DC and AC-based characterizations. In particular, impedance spectroscopy was employed as an AC-based characterization tool. Frequency-dependent impedance spectroscopy have been widely applied to a number of electroceramic materials, such as varistors, MLCCs, solid electrolytes, etc. Impedance spectroscopy provides powerful information on the materials system: i) the simultaneous measurement of conductivity and dielectric constants, ii) systematic identification of electrical origins among bulk-, grain boundary-, and electrode-based responses, and iii) the numerical estimation on the uniformity of the electrical origins. Impedance spectroscopy was applied to the $LaAlO_3/Sr_xCa_{1-x}TiO_3/SrTiO_3$ system, in order to understand the 2-dimensional transports in terms of the interfacial design concepts. The 2-dimensional conduction behavior system is analyzed with special emphasis on the underlying mechanisms. Such approach is discussed towards rational optimization of the 2-dimensional nanoelectronic devices.

• Korean Chemical Engineering Research
• /
• 제53권6호
• /
• pp.709-716
• /
• 2015

본 연구에서는 폴리프로필렌/아이오노머/클레이 삼상 복합체에서 클레이의 분산 및 위치에 따른 복합체의 구조변화와 물성을 연구하였다. 폴리프로필렌 90 wt%, 아이오노머 10 wt%의 블렌드에 클레이를 0~10 wt% 첨가하면서 물성변화를 관찰하였다. 클레이 함량 3%이하의 복합체에서 클레이는 아이오노머 상의 내부에 존재하는 반면, 클레이 함량이 증가하면서 분산상에 클레이가 채워져 견고한 구조가 형성되며 추가적인 클레이는 계면에 존재하게 된다. 이에 따라 계면에서의 상호작용은 폴리프로필렌과 아이오노머로부터 폴리프로필렌-클레이와 아이오노머-클레이의 상호작용으로 변화하며 이에 따라 미세구조 및 유변물성이 변화한다. 복합체의 저장 모듈러스(G')는 클레이가 분산상의 내부에 존재할 때는 거의 영향을 받지 않지만 클레이가 계면에 위치하면서부터 크게 증가한다. 또한 파단면의 모폴로지 역시 클레이가 복합체의 내부에만 존재할 경우에는 분산상의 상 경계가 뚜렷하게 관찰되고 분산상의 크기가 증가하지만, 클레이가 계면에 위치할 때는 분산상의 크기가 줄어들고 파단면의 모폴로지 역시 상의 경계가 뚜렷하게 관찰되지 않는 상용화된 모폴로지를 보인다. 우리는 복합체의 유변물성의 변화를 통하여 분산상 내부구조의 변화에 따른 클레이의 위치변화와 계면에서의 상호작용의 변화를 정량화 하였다. 또한 고체상태에서의 계면 접착량 측정을 통하여 계면에서의 상호작용의 증가함에 따라 접착력이 증가하고, 미세구조상 클레이 입자가 계면에 존재할 때 결정화도가 낮아짐을 확인하였다.

• 한국전산구조공학회논문집
• /
• 제32권4호
• /
• pp.215-222
• /
• 2019

복합재료의 열전달 문제는 일반적으로 만족시켜야 하는 보존방정식과 경계조건 외에 추가적으로 만족시켜야 하는 계면경계조건의 존재로 인해 새로운 수치기법의 개발에 어려움이 있다. 계면경계조건이 미분방정식의 해에 불연속성을 유발시키기 때문에 이것을 적절하게 처리할 수 있는 특수한 함수의 도입이 필요하며, 이산화를 통한 계 방정식의 구성도 쉽지 않다. 본 논문에서는 계면경계의 불연속성을 모사하는 특수함수를 포함하면서 계면경계조건을 항상 만족시킬 수 있도록 계면경계식 자체를 매입한 미분근사식을 제안하고, 불연속 재료상수를 갖는 열전달 문제를 무요소 강형식으로 이산화한 이동최소제곱 차분법을 제시한다. 개발된 수치기법은 기존의 수치기법들과 달리 수치적분과 계면경계조건을 만족시키기 위한 별도의 구속 방정식이 필요없으며, 빠르고 정확하게 이종재료 열전달 문제의 수치해를 구해준다. 개발된 수치기법으로 다양한 복합재료 열전달 문제를 해석하고 오차의 수렴률을 조사한 결과, 높은 정확성과 계산 효율성을 갖는다는 것을 확인할 수 있었으며, 특히, 계면경계가 기하학적 특이성을 나타내는 문제에서도 우수한 성능을 발휘하는 것을 보였다.

• 대한기계학회논문집A
• /
• 제34권10호
• /
• pp.1471-1478
• /
• 2010

미세성형 공정은 마이크로 크기의 부품 생산에 있어 다양한 재료의 활용, 높은 생산성, 적은 재료의 손실, 고품질 생산을 실현할 수 있는 방법으로 최근 산업계와 학계의 많은 주목을 받고 있다. 하지만 매크로 성형에서 마찰거동을 묘사하기 위한 기존의 모델들은 미세성형에서 많은 오차를 유발하는 것으로 알려져 있다. 따라서 미세성형 공정의 성공적인 개발과 실용화를 위해서는 마찰거동의 크기효과에 대한 심도 있는 연구가 필요하다. 본 연구에서는 다양한 크기의 알루미늄 및 황동 재료를 대상으로 링 압축시험을 실시하여 소재의 크기에 대한 마찰거동의 크기효과를 고찰하였다. 유한요소해석을 이용하여 링 압축 시 접촉면의 마찰력이 링 시편의 변형특성에 미치는 영향을 정량적으로 분석하였다. 또한 미끄럼선장 모델링과 상계해석을 응용한 마찰모델을 활용하여 미세성형에서의 마찰거동 특성을 이론적으로 설명하였다.

• Computers and Concrete
• /
• 제10권2호
• /
• pp.135-147
• /
• 2012

At mesoscale, concrete is considered as a three-phase composite material consisting of the aggregate particles, the cement matrix and the interfacial transition zone (ITZ). The reconstruction of the internal structures for concrete composites requires the identification of the boundary of the aggregate particles and the cement matrix using digital imaging technology followed by post-processing through MATLAB. A parameter study covers the subsection transformation, median filter, and open and close operation of the digital image sample to obtain the optimal parameter for performing the image processing technology. The subsection transformation is performed using a grey histogram of the digital image samples with a threshold value of [120, 210] followed by median filtering with a $16{\times}16$ square module based on the dimensions of the aggregate particles and their internal impurity. We then select a "disk" tectonic structure with a specific radius, which performs open and close operations on the images. The edges of the aggregate particles (similar to the original digital images) are obtained using the canny edge detection method. The finite element model at mesoscale can be established using the proposed image processing technology. The location of the crack determined through the numerical method is identical to the experimental result, and the load-displacement curve determined through the numerical method is in close agreement with the experimental results. Comparisons of the numerical and experimental results show that the proposed image processing technology is highly effective in reconstructing the internal structures of concrete composites.

• 한국세라믹학회지
• /
• 제31권12호
• /
• pp.1429-1436
• /
• 1994

We have prepared Ba0.5Sr0.5TiO3 thin films on Si substrate without buffer layer. Deposition was carried out by off-axis rf magnetron sputtering method using Ba0.5Sr0.5TiO3 stoichiometric target. The substrate temperature was changed from 40$0^{\circ}C$ to $700^{\circ}C$ during deposition. As the substrate temperature increased, relative intensity of (110) peak increased up to $600^{\circ}C$, however preferred orientation changed from (110) to (h00) beyond $650^{\circ}C$ of substrate temperature. Deposited films showed microstructures with fine grains whose diameters are less than 100 nm, and columnar structure was observed in the cross-sectional SEM micrograph. AES depth profile showed no significant diffusion at the interfacial reaction area. The effective dielectric constant of films showed maximum value at $600^{\circ}C$, and the leakage current increased with increasing substrate temperature, which may be ascribed to the crystallization of amorphous phases at grain boundary.

• 한국세라믹학회지
• /
• 제47권1호
• /
• pp.75-81
• /
• 2010

The feasibility of using the thin film technology in utilizing lanthanum strontium manganite (LSM) for a solid oxide fuel cell (SOFC) cathode in a low-temperature regime is investigated in this study. Thin film LSM cathodes were fabricated using pulsed laser deposition (PLD) on anode-supported SOFCs with yttria-stabilized zirconia (YSZ) electrolytes. Although cells with a 1 ${\mu}m$-thick LSM cathode showed poor low-temperature cell performance compared to that of a cell with a bulk-processed cathode due to the lack of a triple-phase boundary length, the cell with 200 nm-thick gadolinia-doped ceria (GDC) inserted between the LSM and YSZ showed enhanced performance and more stable operation characteristics in a comparison of a cell without a GDC layer. We postulate that the GDC layer likely improved the cathode adhesion, therefore contributing to the improvement of the cell performance instead of serving as an interfacial reaction buffer.

• Steel and Composite Structures
• /
• 제20권5호
• /
• pp.1023-1042
• /
• 2016

Based on Hamilton's principle, the flexural vibration differential equations and boundary conditions of the steel-concrete composite beam (SCCB) with comprehensive consideration of the influences of the shear deformation, interface slip and longitudinal inertia of motion were derived. The analytical natural frequencies of flexural vibration were compared with available results previously observed by the experiments, the results calculated by the FE model and the other similar beam theories available in the open literatures. The comparison results showed that, the calculation results of the analytical and Timoshenko models had a good agreement with the results of the experimental test and FE model. Finally, the influences of shear deformation and interface slip on the flexural natural frequencies of the SCCB were discussed. The shear deformation effect increases with the increase of the mode orders of flexural natural vibration, and the flexural natural frequencies of the higher mode orders ignoring the influence of shear deformations effect would be overestimated. The interface slip effect decrease with the increase of the mode orders of flexural natural vibration, and the influence of the interface slip effect on flexural natural frequencies of the low mode orders is significant. The influence of the degree of shear connection on shear deformation effect is insignificant, and the low order modes of flexural natural vibration are mainly composed of the rotational displacement of cross sections.

• The Korean Journal of Ceramics
• /
• 제6권3호
• /
• pp.258-261
• /
• 2000

Highly (h00)-oriented (Ba, Sr)TiO$_3$(BST) thin films were grown by pulsed laser deposition on the perovskite LaNiO$_3$(LNO) metallic oxide layer as a bottom electrode. The LNO films were deposited on SiO$_2$/Si substrates by rf-magnetron sputtering method. The crystalline phases of the BST film were characterized by x-ray $\theta$-2$\theta$, $\omega$-rocking curve and $\psi$-scan diffraction measurements. The surface microsturcture observed by scanning electron microscopy was very dense and smooth. The low-frequency dielectric responses of the BST films grown at various substrate temperatures were measured as a function of frequency in the frequency range from 0.1 Hz to 10 MHz. The BST films have the dielectric constant of 265 at 1 kHz and showed multiple dielectric relaxation at the low frequency region. The origin of these low-frequency dielectric relaxation are attributed to the ionized space charge carriers such as the oxygen vacancies and defects in BST film, the interfacial polarization in the grain boundary region and the electrode polarization. We studied also on the capacitance-voltage characteristics of BST films.

• 한국실내디자인학회논문집
• /
• 제18권6호
• /
• pp.96-103
• /
• 2009

Man has an unconscious desire to free oneself from everyday selves and a strong intellectual desire to see and analyze things in a different perspective. This provided a momentum for architectural design that has long been confined to its limits of modernism of being rational and objective. The ever-changing society that we live in filled with various attempts and pluralistic characteristics shows a complex set of attributes that can hardly be defined by a single term. As society moves towards an uncertain and volatile state, the boundary between literature, philosophy and art has dimmed out and converged. Such tendencies have been observable in recent establishments in architecture in the form of introducing external elements and create an alien and farfetched architectural space. Using the 'depaysement' defamiliarization method expressing irrationality and randomness, it is applied in various aspects, sharing the counter-rational structure and features of such architectural space. Hence, it is the purpose of this study to delve into the unique characteristics of depaysement through Magritte's work which reflects the unique pictorial world built under the influence of surrealism, and discover the $D\acute{e}paysement$ tendencies in modern architectural space. It is apparent in Modern architecture that, owing to the development in digital technology, it is showing process changes in design and an interfacial $D\acute{e}paysement$ effect in cyberspace, an interlace of reality and the virtual world. In this study, the focus of analysis was architectural properties such as the program, figure/spatial, material and the objective side, but due to mutual text properties, it is bound to be an overlapping analysis.