Search

In a post-tensioned precast concrete beam–column connection, the precast beams are post-tensioned to ensure the integrity of the connection and to provide recentring characteristics when the connection is subjected to seismic loads. In this study, the post-tensioned precast concrete beam–column connections were tested under reverse-cyclic loading with the test variables of grout strength at the beam–column interface and prestressing stress of stands. The test results showed that the post-tensioned precast concrete beam–column connections have a seismic performance equivalent to that of a conventional reinforced concrete beam–column connection. When high prestress is applied, however, confinement reinforcement is required at the beam ends to secure sufficient deformation capacity without crushing of concrete. An analysis model for post-tensioned precast concrete beam–column connections is also proposed; the model considers the bond properties of prestressing strands, and provides good agreement with the experimental results.

Titanium nitride (TiN) thin films grown by atomic layer deposition (ALD) have attracted considerable attention as electrode materials in semiconductor device applications, such as logic transistors...

Amorphous In-Ga-Zn-O experiences device instability in thin-film transistors (TFTs) due to the vulnerability of oxide channel materials under ambient conditions. Nitrogenation of In-Ga-Zn-O TFTs by partial oxygen substation of nitrogen was performed to enhance stability. The nitrogenated In-Ga-Zn-O thin films were deposited under plasma conditions involving nitrogen gas molecules. The TFT stability was tested under various conditions of temperature, illumination, time, and sweeping. Despite the minor weakness at elevated operation temperature, the nitrogenated In-Ga-Zn-O TFTs exhibited superior tolerance against sweeping operations in TFT devices, illumination, and time-dependent degradation. The improved stability is attributed to the incorporation of nitrogen into In-Ga-Zn-O via oxygen vacancy and its corresponding interface trap improvement.

Electrodes composed of multilayered graphene grown on a metal foam (GMF) were prepared by directly growing multilayer graphene sheets on a three-dimensional (3D) Ni-foam substrate via a self-catalyzing chemical vapor deposition process. The multilayer graphene sheets are successfully grown on the Ni-foam substrate surface, maintaining the unique 3D macroporous structure of the Ni foam. The potential use of GMF electrodes in nonaqueous redox flow batteries (RFBs) is carefully examined using [Co(bpy)3]+/2+ and [Fe(bpy)3]2+/3+ redox couples. The GMF electrodes display a much improved electrochemical activity and enhanced kinetics toward the [Co(bpy)3]+/2+ (anolyte) and [Fe(bpy)3]2+/3+ (catholyte) redox couples, compared with the bare Ni metal foam electrodes, suggesting that the 2D graphene sheets having lots of interdomain defects provide sufficient reaction sites and secure electric-conduction pathways. Consequently, a nonaqueous RFB cell assembled with GMF electrodes exhibits high Coulombic and voltage ef...

Analogous to organic light-emitting diode (OLED), quantum dot-light-emitting diode (QLED) possesses a high eligibility with respect to device structure for the transformation to transparent device that may be pursued as a next-generation display. We report the fabrication of a series of highly transparent mono-colored blue, green, and red QLEDs with a standard architecture simply by replacing thermally evaporated Al with sputtered indium tin oxide (ITO) film as a top cathode. To alleviate the sputtering damage on the underlying electron transport layer while securing a reasonable sheet resistance of ITO film, a moderate sputtering power is judiciously chosen to attain high device performance. Fabrication of a transparent tri-colored white or full-color-capable QLED, comprising an emitting layer mixed with three primary colored QDs, is also demonstrated and further implemented on a flexible substrate of polyethylene naphthalate to additionally offer its feasibility toward transparent flexible device.

Xe-arc flashings of 0.4–1.0 ms in pulse duration annealed indium tin oxide (ITO) thin-films deposited on flexible polymeric substrates at room temperature. As flexible substrates, highly transparent polyimide (PI) thin-films of 16 μm in thickness were prepared on a carrier glass. Measuring optical characteristics of the ITO and the PI thin-films and using the Maxwell equations, we estimated complex refractive indices of ITO and PI materials. With the use of these optical properties, one-dimensional conduction/radiation heat transfer simulation was carried out to predict the temperature variations in the specimens, assuring that the temperature in the ITO thin-film during the flash lamp annealing (FLA) process exceeded its crystallization point. Experimental FLA process resulted in a significant enhancement of the electrical conductivities as well as in a slight increase of optical transmittances of the specimen and was compared with the conventional furnace annealing (CFA) process of 1 h. Microscopic changes in the specimen during the annealing processes were compared using the X-ray diffraction pattern, atomic force microscope, and scanning electron microscope (SEM) measurements. Especially SEM images confirmed that sudden degradations in the electrical conductivities of ITO thin-films observed under higher power FLA or higher temperature CFA conditions were strongly related to the physical damages in the thin-films, which were incurred due to the thermal expansion mismatch between the ITO thin-film and the PI substrate at high temperatures.

Nanocrystalline Sm 2 O 3 -Doped CeO 2 (SDC) powders were synthesized in a single- and two-phase material system by using sonochemical processing with high-frequency agitation. The synthesized SDC nanocrystalline powders were used to coat the mixed-conducting La 0.6 Sr 0.4 CoO 3 (LSC) cathode materials. The combined synthesis processing allows the artificial coating of the LSC materials with the ionic-conducting SDC electrolyte. The electrochemical polarizations of the SDC/LSC composites are characterized using a geometrically constricted contact between the ionic probe and the SDC/LSC composites. The lowest cathode polarization was obtained for the LSC (85 wt%)/SDC (15 wt%). The lowest electrode polarization is believed to result from the high density of the triple-phase boundaries when the constituent phases are interconnected in a 3-dimensional manner.

Steel fiber-reinforced prestressed concrete (SFRPSC) members typically have high shear strength and deformation capability, compared to conventional prestressed concrete (PSC) members, due to the resistance provided by steel fibers at the crack surface after the onset of diagonal cracking. In this study, shear tests were conducted on the SFRPSC members with the test variables of concrete compressive strength, fiber volume fraction, and prestressing force level. Their localized behavior around the critical shear cracks was measured by a non-contact image-based displacement measurement system, and thus their shear deformation was thoroughly investigated. The tested SFRPSC members showed higher shear strengths as the concrete compressive strength or the level of prestress increased, and their stiffnesses did not change significantly, even after diagonal cracking due to the resistance of steel fibers. As the level of prestress increased, the shear deformation was contributed by the crack opening displacement more than the slip displacement. In addition, the local displacements around the shear crack progressed toward directions that differ from those expected by the principal strain angles that can be typically obtained from the average strains of the concrete element. Thus, this localized deformation characteristics around the shear cracks should be considered when measuring the local deformation of concrete elements near discrete cracks or when calculating the local stresses.

Frequency-dependent impedance spectroscopy was applied to the 2-dimensioanl conduction transport in the LaAlO 3 /Sr x Ca 1− x TiO 3 /SrTiO 3 system. The 2-dimensional conduction modifies the electrical/dielectric responses of the LaAlO 3 /Sr x Ca 1− x TiO 3 /SrTiO 3 depending on the magnitude of the interfacial 2-dimensional resistance. The high conduction of the 2-dimensional electron gas (2DEG) layer can be described using a metallic resistor in series with two parallel RC circuits. However, the high resistance of the 2-dimensional layer drives the composite system from a finite low resistor in parallel with the surrounding dielectrics composed of LaAlO 3 and SrTiO 3 materials to a dielectric capacitor. This change in the resistance of the 2-dimensional layers modifies the overall impedance enabled by the presence of the interfacial layer due to Sr x Ca 1− x TiO 3 , which alters the charge transport of the 2-dimensional layer from metallic to semiconducting conduction. A noticeable change is observed in the capacitance Bode plots, indicating highly amplified dielectric constants compared with the pristine SrTiO 3 substrates and Sr x Ca 1− x TiO 3 with a greater Ca content.

Automated semantic segmentation is applied to the quantification of microstructural features in three-phase composite cathode materials of solid oxide fuel cells (SOFCs), i.e., GDC/LSC/Pore where GDC stands for Gd2O3-doped CeO2 and LSC for La0.6Sr0.4CoO3-δ. Our aim is to eliminate the tedious involvement of human experts and the associated errors. The high volume of image information sets is generated using automatic acquisition systems involving focused-ion beam scanning electron microscopy through a so-called slice-view procedure. Through the integration of semantic segmentation with image processing-assisted stereography tools, the following detailed microstructural features are quantitatively extracted automatically and objectively without any human involvement: size distribution, surface (or equivalently, volume) fraction, lengths of two-phase boundaries, and density of triple-phase boundaries based on two-dimensional images. The extracted two-dimensional information is connected with three-dimensional reconstruction analysis. The implications of semantic segmentation in SOFCs are discussed considering efficient analysis and design of high-performance electrode structures in energy-oriented devices.

To date, most of the studies on quantum dot-light-emitting diodes (QLEDs) have been dedicated to the fabrication of high-efficiency monochromatic devices. However, for the ultimate application of QLEDs to the next-generation display devices, QLEDs should possess a full-color emissivity. In this study, we report the fabrication of all-solution-processed full-color-capable white QLEDs with a standard device architecture, where sequentially stacked blue (B)/green (G)/red (R) quantum dot (QD)-emitting layers (EMLs) are sandwiched by poly(9-vinylcarbazole) as the hole transport layer and ZnO nanoparticles (NPs) as the electron transport layer. To produce interlayer mixing-free, well-defined B/G/R QD layering assemblies via successive spin casting, an ultrathin ZnO NP buffer is inserted between different-colored QD layers. The present full-color-capable white QLED exhibits high device performance with the maximum values of 16 241 cd m−2 for luminance and 6.8% for external quantum efficiency. The promising results indicate that our novel EML design of ZnO NP buffer-mediated QD layer stacking may afford a viable means towards bright, efficient full-color-capable white devices.

In this study, shear tests on steel fiber reinforced-prestressed concrete (SFR-PSC) members were conducted with test parameters of the concrete compressive strength, the volume fraction of steel fibers, and the level of effective prestress. The SFR-PSC members showed higher shear strengths and stiffness after diagonal cracking compared to the conventional prestressed concrete (PSC) members without steel fibers. In addition, their shear deformational behavior was measured using the image-based non-contact displacement measurement system, which was then compared to the results of nonlinear finite element analyses (NLFEA). In the NLFEA proposed in this study, a bi-axial tensile behavior model, which can reflect the tensile behavior of the steel fiber-reinforced concrete (SFRC) in a simple manner, was introduced into the smeared crack truss model. The NLFEA model proposed in this study provided a good estimation of shear behavior of the SFRPSC members, such as the stiffness, strengths, and failure modes, reflecting the effect of the key influential factors.

Using a Xe-arc flashing of 0.4 ms, indium tin oxide (ITO) thin-films widely applied to fabricate transparent conducting electrodes for solar cells and displays are annealed at room temperature in order to improve their electric conductance and optical transmittances. ITO thin-films of 100 nm in thickness are deposited on a glass substrate of 500 μm in thickness by the magnetron sputtering method. Ray-tracing calculation estimates that heat absorbed in the thin-film during flash lamp annealing (FLA) process with using an additional back-reflector increases by about 2.8 times greater than that without using the back-reflector. Simulation based on one-dimensional conduction/radiation heat transfer model shows that the film temperatures during the FLA process exceed the crystallization point of the ITO material, indicating that its physical properties have been varied accordingly. Undergoing the short experimental FLA process, resistivity of the specimen has been decreased by about 30%, which is comparable to the ones obtained from conventional furnace annealing at temperatures ranging 200–300 °C for an hour, while the transmittances in the visible light range have been slightly increased. Morphological features of the films are investigated using XRD, XPS, AFM, and SEM, indicating that the specimens treated by the FLA or in furnace have crystallites larger than that of the as-received.

Design codes have specified the minimum shear reinforcement requirement for reinforced concrete (RC) and prestressed concrete (PSC) members to prevent brittle and premature shear failure. They are, however, very different from one another, and particularly, ACI318 code allows the required minimum shear reinforcement to be reduced in PSC members, compared to that in RC members, by specifying the additional equation for PSC members whose basis is not clear. In this paper, the minimum shear reinforcement ratio for PSC members was proposed, which can provide a sufficient reserved shear strength and deformation capacity. The proposed equation was also verified by the test results of PSC specimens lightly reinforced in shear, comparing to design codes and other proposed equations from previous studies.

This study introduces two analytical approaches to estimate the torsional behavior of steel fiber reinforced concrete (SFRC) members. The first approach utilized the tensile constitutive relationship of SFRC in tension derived from SFRC panel test results, and the second approach adopted the direct tension force transfer model, which were applied to the smeared-truss model. In addition, three torsional members including two SFRC specimens with large amounts of transverse reinforcement were tested, and twenty-three SFRC torsional specimens were collected from literature to verify the proposed models. From this study, it appears that the proposed approaches provide enhanced analysis accuracy in estimating the torsional capacities of SFRC members, and closely capture their overall torsional responses compared to other models examined in this study.

Impedance spectroscopy was applied to 2-dimensional graphene materials that were thermally grown on copper substrates to quantitatively monitor the quality of the as-grown graphene materials without the subsequent transfer process. The presence of the graphene layer prevents the dissolution of the metallic copper elements in the corrosive electrolyte and provides an interface between the ionic electrolyte and electronic graphene/copper materials. The highest impedance appears at the graphene/electrolyte to be associated with electrochemically robust graphene materials, i.e., the as-grown graphene materials subjected to atomic layer deposition of Al 2 O 3 . Such an effect is attributed to the anti-corrosive protection of graphene materials and the defect-curing function of Al 2 O 3 in graphene materials. The impedance-based information can be exploited in-situ without the use of any destructive approaches to evaluate the electrical perfectness vulnerable to preparation environments.

The delamination of oxygen electrode during the electrolysis mode operation, which is mainly attributed to interfacial stress arising from the inability of oxygen electrode to accommodate oxygen species transported by oxide ion conducting electrolyte at the three phase boundary (TPB), has been major concern in the development of reversible solid oxide cell (RSOC) systems. The use of lanthanum nickelate, La2NiO4+δ (LNO) as a RSOC oxygen electrode, because of its ability to accommodate excess oxygen species in interstitial positions, can be helpful in reliving such interfacial stresses and thus mitigating the problem of delamination. In this work, the possibility of using LNO as an oxygen electrode in RSOCs is examined. The button cells with 10% gadolinium doped ceria (GDC10) electrolyte, Ni-GDC10 fuel electrode and LNO oxygen electrode are fabricated and their current–voltage–power (I–V–P) performance is analyzed in different gas conditions while operating in fuel cell mode in 500–650 °C range. The button cell shows a maximum power density of ~0.19 W cm−2 at a current density of ~0.5 A cm−2 at 650 °C. Electrochemical impedance spectroscopy was performed in open circuit voltage (OCV) condition to analyze the various factors affecting the fuel cell performance. The long term operation of the fuel cell at a fixed input current of 0.1 A cm−2 for 100 h at 600 °C indicates that the fuel cell is capable of stable performance. The microstructural analysis of the fuel cell after the long term operations indicates no structural degradation.

Double (or layered) perovskite GdBaCo 2 O 5+ δ (GBCO) was synthesized via a glycin nitrate process. This mixed ionic-electronic GBCO was composited to ionic GDC conductors as a cathode system for intermediate-temperature solid oxide fuel cells. The electrochemical features of these GBCO/GDC cathodes were investigated via frequency-dependent impedance spectroscopy with a geometric restriction at the cathode/electrolyte interface. Compared to the pure GBCO system, the GBCO/GDC composites exhibited a gradual increase in their electrochemical polarization. The optimized composition was determined to be 75 wt%:25 wt% GBCO:GDC. The larger GBCO fraction is believed to exhibit high mixed ionic-electronic conduction due to the oxygen vacancies in its crystal structure, found in the [Gd–O] layers.

High-frequency sonication at 20 kHz was employed to coat micro-scale Sm x Sr 1− x CoO 3 (SSC) particles with nano-scale Gd 2 O 3 -doped CeO 2 (GDC) electrolyte materials. The composition-controlled GDC/SSC composite cathodes were evaluated simultaneously using scanning electron microscopy and electrochemical impedance spectroscopy. The microstructurally optimized SSC/GDC cathode composites exhibited minimal electrode polarization compared to the pristine mixed–ionic–electronic conducting SSC materials. The artificially designed micro/nano-composite cathode materials can be employed in intermediate-temperature solid oxide fuel cells.

Boron-implanted polycrystalline Si thin films on glass substrates were subjected to a short duration (1 ms) of intense visible light irradiation generated via a high-powered Xe arc lamp. The disordered Si atomic structure absorbs the intense visible light resulting from flash lamp annealing. The subsequent rapid heating results in the electrical activation of boron-implanted Si thin films, which is empirically observed using Hall measurements. The electrical activation is verified by the observed increase in the crystalline component of the Si structures resulting in higher transmittance. The feasibility of flash lamp annealing has also been demonstrated via a theoretical thermal prediction, indicating that the flash lamp annealing is applicable to low-temperature polycrystalline Si thin films.

Thermal warpage of a glass substrate after a flash lamp annealing process for crystallization of amorphous silicon thin-film is critical to subsequent fabrication processes for manufacturing large-scale displays. This phenomenon is understood through the structural mismatching of hypothetical two-layers in a homogeneous glass structure: thermally softened and uninfluenced, and is mechanistically different from that induced by the mismatch in coefficients of thermal expansions among heterogeneous thin-film structures. Thin subsurface region experiencing the intensified heating is softened, the stress in the region is relaxed, and finally the softened region is shrunk laterally, while uninfluenced part of the substrate remains as it is. The model assumes that the shrunk subsurface layer, of which the thickness is proportional to the thermal penetration, is bonded to the uninfluenced part completely. Due to structural mismatching the substrate is deformed considerably and warped towards the light source (the flash lamp) according to the curvature-flash duration relationship, γ = C2η(1 − C1η1/2). This relationship is confirmed by numerical simulation results based on a viscoelastic model and by experimental observations.

Micro-contact printing of self-assembly monolayers (SAMs), i.e., octadecyl-trichlorosilane (OTS) was combined with self limiting atomic layer deposition in order to fabricate the selective deposition of nickel oxide on amorphous Si thin films. The localized nickel species facilitated metal-induced crystallization (MIC) and at later stages, metal-induced lateral crystallization (MILC) in amorphous Si thin films at the elevated temperatures ranging from 500 °C to 550 °C. The uniform coating of SAMs onto amorphous Si thin films was monitored using physical/chemical characterization, i.e., atomic force microscopy, electron microscopy, and Raman spectroscopy. The crystalline feature was found to be superior to the counterpart solid-phase crystallization. The effectiveness of SAMs appears to provide the microscale patterning in addition to the sophisticated control against nickel-species.

Aluminum oxide was deposited into the porous cathode compartment of the (Sc,Al)-doped ZrO 2 electrolyte cell through atomic layer deposition involving trimethyl aluminum and water as aluminum and oxygen sources, respectively. The deposited aluminum oxide had a detrimental effect on the cell performance of the zirconia-based SOFC unit cells in terms of the output power but did not change the open-cell voltage. Based on impedance spectroscopy, the open-cell voltage, and the output performance, the resultant degradation is attributed to the geometrical blockade of functional triple phase boundaries in La 0.6 Sr 0.4 CoO 3 (LSCo)-based cathode materials of mixed ionic electronic conduction, indicating that there is a disruption at the interface between the charge collector and cathode that is proportional to the amount of deposited Al 2 O 3 .

An experimental Portland cement (EPC) was manufactured with pure raw materials under controlled laboratory conditions. The physical properties and biocompatibility of EPC was compared with that of ProRoot MTA. The microstructure and chemical composition of EPC was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The cytotoxicity of the extracts of EPC and ProRoot MTA on MG-63 cells was evaluated by using a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) assay. The setting process was monitored by electrochemical impedance spectroscopy (EIS) and the electrical responses obtained with respect to time were analyzed using equivalent circuit models to separate bulk and electrode response. The EPC paste showed higher electrical conductivity than ProRoot MTA and it set slowly, which could be due to the presence of excess CaO in EPC composition.

Recognizing that steel fibers can supplement the brittle tensile characteristics of concrete, many studies have been conducted on the shear performance of steel fiber reinforced concrete (SFRC) members. However, previous studies were mostly focused on the shear strength and proposed empirical shear strength equations based on their experimental results. Thus, this study attempts to estimate the strains and stresses in steel fibers by considering the detailed characteristics of steel fibers in SFRC members, from which more accurate estimation on the shear behavior and strength of SFRC members is possible, and the failure mode of steel fibers can be also identified. Four shear behavior models for SFRC members have been proposed, which have been modified from the softened truss models for reinforced concrete members, and they can estimate the contribution of steel fibers to the total shear strength of the SFRC member. The performances of all the models proposed in this study were also evaluated by a large number of test results. The contribution of steel fibers to the shear strength varied from 5% to 50% according to their amount, and the most optimized volume fraction of steel fibers was estimated as 1%-1.5%, in terms of shear performance.

Modern structural concrete members have become longer and slender, and the prestressed concrete method is an efficient way for sufficiently satisfying the strength and serviceability requirements of such members. Particularly, pretensioned concrete members are typically produced as a precast system that can reduce the construction time and waste significantly by minimizing on-site work. Thus, the pretensioned precast concrete structure is an effective method that can meet both environmental and economic demands in international society. Productivity of the pretensioned members, however, is significantly influenced by the timing of releasing prestress, because prestressing forces can be transferred when the target compressive strength of early age concrete is attained. Unfortunately, the allowable compressive stress at transfer specified in current design code provisions may not be reliable in some practical situations, and those stress limits were determined by empirical methods without a theoretical basis. To overcome such problems, a reasonable estimation equation for allowable compressive stress at transfer was proposed in this paper using extensive analyses based on the Strength Design Method (SDM), in which the eccentricity ratio of the tendon, the sectional size and shape, the level of prestress, and the self-weight moment were considered. The allowable releasing compressive stresses specified in international design codes and based on the proposed equation were compared to test results collected from literature. These comparisons indicated that the allowable stresses specified in current design codes provided unconservative evaluation results for pretensioned members with low eccentricity ratios and conservative results for those with high eccentricity ratios, while the proposed equation reasonably evaluated the allowable compressive stresses of pretensioned members with rectangular, tee, and inverted tee sections.

Steel-fiber-reinforced concrete (SFRC) is an efficient cement-based composite material that can compensate for the drawbacks of the material properties of conventional concrete and has better structural performances than conventional concrete. It can improve torsional behavior as well as flexural and shear behavior. However, analysis of the torsional behavior of SFRC members is quite complicated because force equilibrium and strain compatibility in a three-dimensional space should be satisfied. Accordingly, many studies proposed empirical evaluation equations for the torsional strength of SFRC members based on experimental results. Therefore, this study derived a constitutive model of SFRC in tension, which greatly influences the torsional behavior of SFRC, based on the test results of SFRC shear panels under biaxial stress, and this tensile behavior model was introduced to a fixed-angle softened-truss model. A theoretical evaluation model based on the modified fixed-angle model for torsional behavior of SFRC was developed, and the performance of the analytical model was also evaluated compared to test results obtained from literature.

Due to the complex shear mechanism of steel fiber-reinforced concrete (SFRC) members, there is lack of comprehensive shear behavior models for SFRC members. The shear behavior model, based on a smeared crack model, requires the tensile stress–strain constitutive equation of SFRC membrane subjected to biaxial stresses. After SFRC panel tests under biaxial stresses were recently conducted, it has been possible to create a more complete smeared crack model for estimating the shear behavior of SFRC members. It is, however, very difficult to conduct such experiments for different types of steel fibers, various amount of steel fibers, different ranges of concrete strengths, etc. Thus, in this study, steel fibers are modeled as average direct tensile contribution elements in a modified smeared crack truss model, considering directionality and distribution of fibers. In this way, only simple bond tests are required to reflect the effects of different characteristics of SFRC. In addition, the shear contribution of steel fibers can be obtained considering the bond failure of steel fibers. The proposed model was compared to the test results of 8 SFRC panels and 80 SFRC beams, and the shear behavior of the SFRC members was well estimated.

Impedance spectroscopy was used to monitor the hydration in the electrical/dielectric behaviors of chemical mechanical planarization (CMP)-blended cement mixtures. The electrical responses were analyzed using their equivalent circuit models, leading to the separation of the bulk and electrode based responses. The role of the CMP slurry was monitored as a function of the relative compositions of the CMP-blended cements, i.e. water, CMP slurry, and ordinary Portland cement. The presence of Al₂O₃ nanocrystals in the CMP slurries appeared to accelerate the hydration process, along with a more tortuous microstructure in the hydration, with enhanced hydration products. The frequency-dependent impedance spectroscopy was proven to be a highly efficient approach for evaluating the electrical/dielectric monitoring of the change in the pore structure evolution that occurs in CMP-blended cements.

A 532nm Nd:YAG laser was applied to crystallize amorphous Si thin films in order to evaluate the applicability of Nd:YAG laser to low-temperature polycrystalline Si technology. In this study, we aim at enhancing uniformity as well as crystallinity. In order to achieve the goal, a new optical system called as a diffusing system was used to enhance the uniformity of irradiating beam profile, consequently improving the quality of crystallized microstructures. Optimal processing parameters for high crystallinity and uniformity were developed by design of experiments (DOE). To investigate crystallinity and uniformity, Raman spectroscopy and optical microscopy were utilized. Therefore, the effectiveness of Nd:YAG laser is suggested as a feasible alternative that is capable of crystallizing the amorphous Si thin films.

Our understanding on the shear behavior of SFRC members is still quite limited due to the complex inter-combinatorial mechanisms of shear transfer. Some efforts have been made to extend the application of modified compression field theory and the soften truss model to SFRC members. It is difficult, however, for such models to reflect some of the key behavioral characteristics of SFRC, such as the fiber directionality at the crack interfaces, the differences of bond strengths by fiber types, and the pull-out failure of fibers at crack. Thus, in this study, a nonlinear finite element analysis procedure has been developed that sufficiently reflects the material properties and behavioral characteristics of SFRC, and can be applied to obtain the shear behavior. The accuracy and rationality of the proposed model were also verified in this study by comparing to the recent experimental results on the SFRC shear panels.

Although structural concrete is well known for its good economic efficiency, it has limits of structural performance due to the low tensile strength, for which new structural members utilizing various concrete composite materials have been developed. Steel Fiber-Reinforced Concrete(SFRC) has great tensile strength, which is the one of the excellent composite material to complement the weakness of concrete, and it is also considered as a good alternative to prevent the explosive failure of high strength concrete under fire. Also, prestressed concrete members are of great advantages to long span structures and have greater shear strength compared to conventional reinforced concrete members. In this research, thus, a total of 22 direct shear test specimens were fabricated and tested to understand the shear behavior of Steel Fiber-Reinforced Prestressed Concrete(SFR-PSC) members, in which SFRC members combined with prestressing method. Based on the test results, the constitutive equations of shear behavior at crack interfaces were proposed, which provided good estimation on the shear behavior of the SFR-PSC direct shear test specimens.

Many studies have been performed on steel fiber-reinforced normal/high-strength concrete (SFRC, SFRHC) for years, which is to improve some of the weak material properties of concrete. Most of equations for material strengths of SFRHC, however, were proposed based on relatively limited test results. In this research, therefore, the material test results of SFR(H)C were extensively collected from literature, and material tests have conducted on SFR(H)C; compressive strength tests, splitting tensile tests, and modulus of rupture tests. Based on the extensive test data obtained from previous studies and this research, a database of SFR(H)C material strengths has been established, and improved equations for material strengths of SFR(H)C were also proposed. Test results showed that both the splitting tensile strength and the modulus of rupture of SFR(H)C increased as the volume fraction of steel fiber increased, while the effect of the steel fiber volume fraction on the compressive strength of SFR(H)C were not clearly observed. The proposed equations for the splitting tensile strength and the modulus of rupture of SFR(H)C showed better results than the previous equations examined in this study in terms of not only accuracy but also safety/reliability.

Atomic layer deposition (ALD) of nickel oxide was applied to the nickel-induced crystallization of amorphous Si thin films. The nickel-induced crystallization was monitored as a function of annealing temperature and time using Raman spectroscopy. Since Raman spectroscopy allows for the numerical quantification of structural components, the incubation time and the crystallization rates were estimated as functions of the annealing temperature. The spatial locations of a nickel-based species, probably NiSi2, were investigated using X-ray photoelectron spectrometry. The formed NiSi2 seeds appeared to accelerate the crystallization kinetics in amorphous Si thin films deposited onto glass substrates. The ramifications of the atomic layer deposition are discussed with regard to large-panel displays, with special emphasis on the sophisticated control of the catalytic elements, especially nickel.

We reports on a unique characterization method for the electrode reactions of SOFCs via impedance spectroscopy combined with a spatially-constricted contact based on a robust electrolyte which is expected to give more reliable measurement set-up. Various electrode materials were chosen to validate our method and the corresponding impedance phenomena were analyzed to give an insight for optimization of the SOFC electrode. The ramifications of "limited-contact" impedance spectroscopy are discussed for an exhaustive understanding of electrode-related polarizations in SOFCs

Gd₂O₃-doped CeO₂2 (GDC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O₃ (LSCF) composite cathode materials were prepared in order to be applied to intermediate-temperature solid oxide fuel cells. The electrochemical polarization was evaluated using ac impedance spectroscopy involving geometric restriction at the interface between an ionic electrolyte and a mixed-conducting cathode. In order to optimize the cathode composites applicable to a GDC electrolyte, the cathode composites were evaluated in terms of polarization losses with regard to a given electrolyte, i.e., GDC electrolyte. The polarization increased significantly with decreasing temperature and was critically dependent on the compositions of the composite cathodes. The optimized cathode composite was found to consist of GDC 50 wt% and LSCF 50 wt%; the corresponding normalized polarization loss was calculated to be 0.64 at 650℃.

A rechargeable lithium–oxygen (Li–O2) battery is considered as a promising technology for electrochemical energy storage systems because its theoretical energy density is much higher than those of state-of-the-art Li-ion batteries. The cathode (positive electrode) for Li–O2 batteries is made of carbon and polymeric binders; however, these constituents undergo parasitic decomposition reactions during battery operation, which in turn causes considerable performance degradation. Therefore, the rational design of the cathode is necessary for building robust and high-performance Li–O2 batteries. Here, a binder-free carbon nanotube (CNT) electrode surface-modified by atomic layer deposition (ALD) of dual acting RuO2 as an inhibitor–promoter is proposed for rechargeable Li–O2 batteries. RuO2 nanoparticles formed directly on the binder-free CNT electrode by ALD play a dual role to inhibit carbon decomposition and to promote Li2O2 decomposition. The binder-free RuO2/CNT cathode with the unique architecture shows outstanding electrochemical performance as characterized by small voltage gaps (∼0.9 V) as well as excellent cyclability without any signs of capacity decay over 80 cycles.

The electrochemical property of SOFC cathode composites based on LSM((La 0.7 Sr 0.3 ) 0.95 MnO 3 ) and YSZ(Y 2 O 3 -Stabilized ZrO 2 ) was characterized by using limited-contact geometry of an electrode and electrolyte in AC two-point impedance analysis. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point-contact of YSZ on the planar LSM/YSZ cathode. The point-contacted interface also amplifies the bulk resistance of the electrolyte and electrode which allows quantitative estimation of the electrode-related responses with regard to the amplified bulk resistance. The resultant impedance spectra were analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The electrode-related polarizations were measured with respect to the cathode composition, temperature and oxygen partial pressure. The potentiality of modified impedance spectroscopy is discussed as an alternative approach toward more precise resolving of the electrode-polarization phenomena in solid oxide fuel cells.

Silicon nitride films for an anti-reflection coating were deposited on silicon via RF magnetron sputtering using a Si3N4 target. The best result was obtained at the sputtering condition of 340W RF power, 5 mtorr Ar atmosphere, 100℃ substrate temperature. The films showed 7.9% reflectance minimum with 2.35 refractive index, 0.21 absorption coefficient at 66.6 ㎚ thickness. The surface morphology showed a smooth and dense film with good adhesion to silicon surface.

Atomic layer deposition of nickel oxide was employed to fabricate polycrystalline Si thin films on glass substrates via metal induced crystallization (MIC).

A composite cathode of LSCF (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O₃) and GDC (Gd₂O₃-doped CeO₂ : Ce 0.9 Gd 0.1 O 1.95 ) was characterized in terms of an electrode response, using a point contact in an Yttria-Stabilized Zirconia (YSZ) electrolyte incorporated into AC two-point impedance spectroscopy. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point contact on the planar LSCF/GDC electrode. The point contact interface increases the bulk resistance allowing the estimation of the point contact geometry and resolving the electrode-related responses. The resultant impedance spectra are analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The bulk responses can be resolved from the electrode-related portions in terms of spreading resistance. The electrode-related polarizations are measured in terms of temperature and oxygen partial pressure. The modified impedance spectroscopy is discussed in terms of methodology and analytical aspects, toward resolving the electrode-polarization issues in solid oxide fuel cells.

Amyloid-beta peptide 42 (Abeta42) mediates neuronal degeneration in Alzheimer's disease (AD). We sought to produce recombinant Abeta42 as an ubiquitin extension. A synthetic oligonucleotide encoding Abeta42 was constructed and cloned as an extended polypeptide of hexahistidine-tagged ubiquitin (H(6)Ub) using the pET vector. Isopropyl-beta-D-thiogalactopyranoside induction of transformed Escherichia coli resulted in the production of large amounts of insoluble H(6)Ub-Abeta42 fusion protein. H(6)Ub-Abeta42 was solubilized in 8 M urea and applied to a nickel-nitrilotriacetic acid affinity column for purification. Column washing removed the urea and soluble H(6)Ub-Abeta42 was eluted, indicating that covalently attached ubiquitin prevented Abeta42 from aggregating. Abeta42 was cleaved from H(6)Ub using recombinant yeast ubiquitin hydrolase-1 (YUH-1) and purified using reverse-phase chromatography. The recombinant Abeta42 prepared in this study has the same toxic effect on human neuroblastoma SH-SY5Y cells comparing with chemically synthesized, commercial one. The peptide yield was more than 4 mg/L culture, indicating this ubiquitin fusion technique is an attractive method for production of aggregation-prone peptides such as Abeta42.

The single-layer 400 μm × 200 μm sized Ba0.6Sr0.4TiO3 thin-film embedded chip capacitors with two external electrodes fabricated on the surface of the chip capacitors have been demonstrated. The structure of the external electrodes placed on the same surface allows the reduction of connection length, resulting in low parasitic loss and noise of elecronic devices. The fabricated chip capacitors exhibited excellent electrical properties such as high capacitance density and dielectric constant (1687 nF/cm2 and 452) and a low dielectric loss of 0.052 at 1 kHz, respectively. In addition, the chip capacitors exhibited the superior temperature stability of X5R (ΔC/C = ±15% at -55°C to +85°C) characteristics. Such a low leakage current density of ~ 0.15 μA/cm2 at 3 V and a high breakdown voltage of 19.75 V were obtained as well. In conclusion, the chip capacitors are suggested as a candidate for the applications of embedded passive components.

Digital quantification of a two-dimensional structure was applied to a GDC(Gd2O3-doped CeO2)/LSM(La0.85Sr0.15MnO3) composite cathode employed for solid oxide fuel cells. With the aid of high-resolution imaging capability based on secondary and backscattered electron images, two-dimensional electron micrographs were converted to digital binary files using an image processing tool combined with the line intercept method. Statistical analysis combined with a metallurgical tool was employed to determine microstructural factors, i.e., volume fraction, size distribution, and interconnectivity. The current work reports the quantification of the two-dimensional structural images of GDC/LSM composites applicable to solid oxide fuel cells, with the aim of obtaining the volume fraction, size distribution, and interconnectivity as functions of composite composition. The volume fractions of the solid constituent phases exhibit compositional dependence in cathodes; however, LSM interconnectivity increases gradually as a function of LSM composition, whereas that of GDC decreases significantly at 50 wt% LSM.

The flat plate slab system is widely used in construction fields due to its excellent constructability and savings in story height compared to the conventional beam-column moment-resisting system. Many researchers are, however, concerned about the punching shear failure that can happen in a two-way flat plate slab system, for which many shear-strength-enhancement techniques have been suggested. One of the effective alternatives is the application of steel-fiber-reinforced concrete. However, most previous studies on the punching shear strength of steel-fiber-reinforced concrete flat slabs had presented empirical formulas based on experimental results. On the other hand, theoretical models proposed in previous studies are difficult to be applied to practical situations. Therefore, in this study, a punching shear strength model of the steel-fiber-reinforced concrete two-way flat slab is proposed. In this model, the total shear resistance of the steel-fiber-reinforced concrete flat slab is expressed by sum of the shear contribution of steel fibers in the cracked tension region and that of intact concrete in the compression zone. A total of 91 shear test data on steel-fiber-reinforced concrete slab–column connection were compared to the analysis results, and the proposed model provided a good accuracy on estimating the punching shear strength of the steel-fiber-reinforced concrete flat slabs.

Activation of polycrystalline silicon (poly-Si) thin films doped as n-type using selective ion implantation of phosphorous was performed employing field-enhanced rapid thermal annealing where rapid thermal annealing of halogen lamps is combined with alternating magnetic fields. The ion activation was evaluated using Hall effect measurements incorporating the resistivity, the charge carrier concentration, and the mobility. Statistical design of experiments is attempted in order to clarify the effects and interactions of processes variables on field-enhanced rapid thermal annealing towards ion activation: the three processing variables are furnace temperature, power of halogen lamp, and the alternating magnetic field. Hall effect measurements indicate that the furnace temperature and RTA power are found to be dominant in activating the doped polycrystalline Si in dose. The activation process results from the competition between charge carrier concentration and mobility: the increase in mobility is larger than the decrease in charge carrier concentration.

We performed capacitance–voltage analysis of 5-nm-thick LaAlO3/SrTiO3 heterostructure containing two-dimensional-electron-gas (2DEG) at the interface. The complex impedance of the heterostructure was measured as a function of frequency for a wide range of gate biases. The impedance spectra showed a different behavior above and below an applied voltage of −1.8 V. The capacitance determined from the impedance was approximately 1.2 nF above −1.8 V and was drastically reduced to ∼0.01 nF below this voltage, owing to depletion of 2DEG and the insulating SrTiO3 underneath it. This suggests that devices utilizing LaAlO3/SrTiO3 can facilitate switching operations in a very small voltage range.

A 532 nm Nd-YAG laser was applied to crystallize amorphous Si thin films in order to evaluate the applicability of a Nd-YAG laser to low-temperature polycrystalline Si technology. The irradiation of a green laser was controlled during the crystallization of amorphous Si thin films deposited onto glass substrates in a sophisticated process. Raman spectroscopy and UV-Visible spectrophotometry were employed to quantify the degree of crystallization in the Si thin films in terms of its optical transmission and vibrational characteristics. The effectiveness of the Nd-YAG laser is suggested as a feasible alternative that is capable of crystallizing the amorphous Si thin films.