Corning (South Korea)

Supercapacitors with porous carbon structures have high energy storage capacity. However, the porous nature of the carbon electrode, composed mainly of carbon nanotubes (CNTs) and graphene oxide (GO) derivatives, negatively impacts the volumetric electrochemical characteristics of the supercapacitors because of poor packing density (<0.5 g cm(-3)). Herein, we report a simple method to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes. Because of their vertically aligned and opened-edge graphene structure, VArGO electrodes displayed high packing density and highly efficient volumetric and areal electrochemical characteristics, very fast electrolyte ion diffusion with rectangular CV curves even at a high scan rate (20 V/s), and the highest volumetric capacitance among known rGO electrodes. Surprisingly, even when the film thickness of the VArGO electrode was increased, its volumetric and areal capacitances were maintained.

Chemically bonded graphene/carbon nanotube composites as flexible supercapacitor electrode materials are synthesized by amide bonding. Carbon nanotubes attached along the edges and onto the surface of graphene act as spacers to increase the electrolyte-accessible surface area. Our lamellar structure electrodes demonstrate the largest volumetric capacitance (165 F cm(-3) ) ever shown by carbon-based electrodes.

Phase-pure solid solutions with the composition of Sr 2 Nb x Ta 2 - x O 7 (SNT, x = 0−2) were prepared at 900 °C for 5 h by the Pechini-type polymerizable complex (PC) technique, based upon polymerization between citric acid and ethylene glycol. The two end compounds, Sr 2 Ta 2 O 7 ( x = 0) and Sr 2 Nb 2 O 7 ( x = 2), produced H 2 and O 2 in a stoichiometric ratio from pure water under UV light irradiation without a NiO cocatalyst. The photocatalytic activity of SNT for the water decomposition was greatly improved by loading NiO as a cocatalyst for a whole range of x . The photocatalytic activity was dramatically decreased approximately by 1 order of magnitude once Ta has been replaced by Nb, even when the amount of Nb was small. For all of the NiO-loaded SNT samples, water was stoichiometrically decomposed into H 2 and O 2 . While samples prior to the complete crystallization showed very low activities despite their high surface area, the corresponding photocatalytic activities of well-crystallized samples depended primarily on their surface area. The low photocatalytic activities of such premature samples were interpreted as a consequence of the increased number of lattice defects acting as inactivation centers. The maximum photocatalytic activity was obtained for NiO (0.15 wt %)/Sr 2 Ta 2 O 7 prepared by the PC method at 800 °C for 48 h; the photocatalyst having a specific surface area of 10.4 m 2 ·g - 1 produced H 2 and O 2 from pure water with specific rates of 3517 and 1733 μmol·h - 1 ·g - 1, respectively, 3.5 times larger than the best result for a sample prepared by the conventional solid-state reaction method.

We report the effects of various substrates and substrate thicknesses on electrospun poly(vinylidene fluoride) (PVDF)-nanofiber-based energy harvesters. The electrospun PVDF nanofibers showed an average diameter of 84.6 ± 23.5 nm. A high relative β-phase fraction (85.2%) was achieved by applying high voltage during electrospinning. The prepared PVDF nanofibers thus generated considerable piezoelectric potential in accordance with the sound-driven mechanical vibrations of the substrates. Slide glass, poly(ethylene terephthalate), poly(ethylene naphthalate), and paper substrates were used to investigate the effects of the intrinsic and extrinsic substrate properties on the piezoelectricity of the energy harvesters. The thinnest paper substrate (66 μm) with a moderate Young's modulus showed the highest voltage output (0.4885 V). We used high-performance 76, 66, and 33 μm thick papers to determine the effect of paper thickness on the output voltage. The thinnest paper substrate resulted in the highest voltage output (0.7781 V), and the numerical analyses of the sound-driven mechanical deformation strongly support the hypothesis that substrate thickness has a considerable effect on piezoelectric performance.

Carbon dioxide (CO2) conversion technology has been estimated as a potentially practical solution for global warming problems although it still has some weaknesses such as cost and energy consumption. In this study, a combined steam reforming process with dry methane reforming process for the CO2 treatment was investigated. Because the dry methane reforming process could generate synthesis gas from carbon dioxide, it could decrease the CO2 emissions from the existing steam reforming process. Models for the steam reforming process and the combined process were developed and extended mitigation cost was suggested to evaluate CO2 reduction of the overall process. The combined process could reduce net CO2 emission by 67% compared with the reference steam reforming process, and the extended mitigation cost of the combined process ranged from 21 to 26.5 (US$/CO2 ton) according to the change of the cost for CO2 transportation.

Abstract Particulate matter (PM) and volatile organic compounds (VOCs) are recognised as hazardous air pollutants threatening human health. Disposable filters are generally used for air purification despite frequent replacement and waste generation problems. However, the development of a novel regenerable and robust filter for long-term use is a huge challenge. Here, we report on a new class of facile water-washing regenerable ceramic catalyst filters (CCFs), developed to simultaneously remove PM (&gt;95%) and VOCs (&gt;82%) in single-pass and maximized space efficiency by coating the inner and outer filter channels with an inorganic membrane and a Cu 2 O/TiO 2 photocatalyst, respectively. The CCFs reveal four-fold increase in the maximum dust loading capacity (approximately 20 g/L) in relation to conventional filters (5 g/L), and can be reused after ten regeneration capability with simple water washing retaining initial PM and VOC removal performances. Thus, the CCFs can be well-suited for indoor and outdoor air purification for 20 years, which shows a huge increase in lifetime compared to the 6-month lifespan of conventional filters. Finally, we believe that the development and implementation of CCFs for air purification can open new avenues for sustainable technology through renewability and zero-waste generation.

Abstract A simple and robust dip‐coating method for fabricating carbon nanotube (CNT) field emitters has been proposed. The thin multiwalled (tMW)CNTs synthesized by CVD were dispersed in various solutions such as N , N‐ dimethylformamide (DMF), isopropyl alcohol (IPA), N ‐methyl‐2‐pyrrolidinone (NMP), and dichloroethane (DCE). The weak adhesion between CNTs and substrate, a serious drawback of the dip‐coating approach, was resolved by anchoring CNTs to the substrate via the melting of an indium layer. We found that the uniformity and density of the CNTs could be optimized by controlling the degree of dispersion of CNTs in solvents. The field‐emission characteristics are also discussed.

The effects of chamber pressure ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) on the structural and chemical properties of an indium gallium tin oxide (IGTO) channel layer were examined. Smoother and denser IGTO films were obtained with decreasing <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , which were explained based on the enhanced kinetic energy of sputtered particles due to fewer collisions with the plasma atmosphere. The resulting IGTO thin-film transistor exhibited a high mobility of 35.0 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, subthreshold gate swing of 0.17 V/decade, threshold voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) of -0.45 V, and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON/OFF</sub> ratio >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> , even at a low annealing temperature of 150 °C.

Understanding the interaction between polyimide and inorganic surfaces is vital in controlling interfacial adhesion behavior. Here, molecular dynamics simulations are employed to study the adhesion of polyimide on both crystalline and glassy silica surfaces, and the effects of hydroxylation, silica structure, and polyimide chemistry on adhesion are investigated. The results reveal that polyimide monomers have stronger adhesion on hydroxylated surfaces compared to nonhydroxylated surfaces. Also, adhesion of polyimide onto silica glass is stronger compared to the corresponding crystalline surfaces. Finally, we explore the molecular origins of adhesion to understand why some polyimide monomers like Kapton have a stronger adhesion per unit area (adhesion density) than others like BPDA-APB. We find this occurs due to a higher density of oxygen’s in the Kapton monomer, which we found to have the highest contribution to adhesion density.

Gallium-doped zinc oxide thin films were prepared on glass substrates by dc magnetron sputtering under various hydrogen contents in sputtering ambient. The carrier concentration of the films deposited at low-temperatures (80 and 160 °C) was increased due to the incorporation of hydrogen atoms, acting as shallow donors. A low resistivity of 4.0×10−4 Ω cm was obtained for the film grown at 160 °C with H2 10%, which has a carrier concentration of 8.2×1020/cm3. The beneficial effect of hydrogen doping was not observed for the films deposited at 270 °C. Both carrier concentration and mobility were decreased by the addition of hydrogen gas in the sputtering ambient. Variations in the electrical transport properties upon vacuum annealing showed that the difference is attributed to the thermal stability of interstitial hydrogen atoms in the films. The hydrogen incorporation was found to induce the lattice expansion and the free carrier absorption in near infrared range. The investigation of the structural and optical properties of the films upon annealing also revealed that the incorporated hydrogen atoms are unstable at high temperature, which is consistent with the results obtained in the electrical properties.

This manuscript provides a comprehensive study of adhesion behavior and its governing mechanisms when polyimide undergoes various modes of detachment from silica glass. Within the framework of steered molecular dynamics, we develop three different adhesion measurement techniques: pulling, peeling, and sliding. Such computational methodologies can be applied to investigate heterogeneous materials with differing interfacial adhesion modes. Here, a novel hybrid potential involving a combination of the INTERFACE force field in conjunction with ReaxFF and including Coulombic and Lennard-Jones interactions is employed to study such interfaces. The studies indicate that the pulling test requires the largest force and the shortest distance to detachment as the interfacial area is separated instantaneously, while the peeling test is observed to exhibit the largest distance for detachment because it separates via line-by-line adhesion. Two kinds of polyimides, aromatic and aliphatic type, are considered to demonstrate the rigidity dependent adhesion properties. The aromatic polyimide, which is more rigid due to the stronger charge transfer complex between chains, requires a greater force but a smaller distance at detachment than the aliphatic polyimide for all of the three methodologies.

Abstract Proposed high‐power electronic and optoelectronic applications of GaN materials rely heavily on the effectiveness of heat removal from the devices. Here we report the results of our measurements of thermal conductivity in the thick free‐standing GaN films prepared by hydride vapor phase epitaxy. The fabrication method allows one to grow the low‐dislocation density films without the use of non‐native substrates. Our experimental data show that the room tempera‐ ture thermal conductivity in free‐standing GaN films can be as high at 225 W/mK, which is a factor of 1.8 increase compared to a reference GaN film grown on sapphire substrate. The modeling, performed for the given sample parameters, indicates that the low‐temperature thermal conductivity can reach a record value of 7460 W/mK. The presented results are important for the thermal management optimization of GaN‐based devices. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Placing the electrical and photonic chiplets in a single package leads to significant power reduction. Chiplets are connected by fine-line electrical routing over a length of a few millimeters and optical interconnects in the package connect photonic chips with optical fibers for off-package communication. A packaging substrate made of glass with optical waveguides, through glass vias and electrical redistribution layers inside a single-sided cavity enables lower-cost assembly. A single-sided 50 μm deep cavity was etched in glass, and electrical copper lines with 5 μm in height and width were deposited on the floor of the cavity. Ion-exchange (IOX) waveguides with propagation loss of <0.1 dB/cm were fabricated below the glass surface. For flip-chip assembly of photonic chips and optical coupling with the IOX waveguides at the top surface of the glass, all electrical interconnects were located inside the cavity. Photonic chips with silicon nitride waveguides were optically coupled to glass waveguides with a minimum loss of 0.5 dB, achieved by fiducial-aligned flip-chip photonic assembly. A low-profile fiber connector with height of 4.4 mm connects the integrated ion-exchanged waveguides with the optical fibers. Average connector loss of 0.83 dB was demonstrated with physical contact between fibers and IOX glass waveguides.

We report a dual-gate, amorphous In-Ga-Sn-O (aIGTO) thin-film transistor (TFT) exhibiting high field-effect mobility (μFE) and very low subthreshold swing. The TFT has a bottom-gate having 5 μm overlap with source/drain (S/D) and a top-gate with 0.5 μm offset with S/D electrodes. The bottom-gate potential is swept at various top-gate voltages. The μFE of a-IGTO TFT is found to be 39.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> which is almost independent of top-gate potential. The subthreshold swing is ~ 0.19 Vdec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and also does not change much with top-gate potential variation between -50 V and +90 V, indicating very low density of states in the gap. The a-IGTO TFT exhibits no effect of negative bias illumination stress.

Orthogonal frequency division multiple access (OFDMA) systems, such as IEEE 802.16e/m and 3GPP Long Term Evolution (LTE), require significantly large signaling overhead for delivering small-sized delay-sensitive traffic such as voice over IP (VoIP) service. It may result in a significant decrease in the spectral efficiency. In order to overcome this drawback, recently, a persistent scheduling scheme has been standardized in standard bodies. In order to reduce the signaling overhead, the modulation and coding scheme (MCS) is set to be fixed during a burst period for the persistent scheduling procedure and an incomplete transmission, if it occurs, is recovered by a hybrid automatic repeat request (HARQ) scheme. In this paper, considering the HARQ retransmissions, we propose a rate selection scheme for the persistent scheduling satisfying given quality of service (QoS) requirements. In our proposed rate selection scheme, we consider two important factors which were not considered in previous HARQ-related work: time-correlations of the wireless channel in the HARQ retransmissions and the resource usage of signaling overhead. Numerical results show that the proposed rate selection scheme can efficiently enhance the utilization of radio resources compared to the conventional schemes.

Atomistic modeling methods are successfully applied to understand interfacial interaction in nanoscale size and analyze adhesion mechanism in the organic-inorganic interface. In this paper, we review recent representative atomistic simulation works, focusing on the interfacial bonding, adhesion strength, and failure behavior between polymer film and silicate glass. The simulation works are described under two categories, namely non-bonded and bonded interaction. In the works for non-bonded interaction, three main interactions, namely van der Waals interaction, polar interaction, and hydrogen bonds, are investigated, and the contributions to interfacial adhesion energy are analyzed. It is revealed that the most dominant interaction for adhesion is hydrogen bonding, but flexibility of the polymer film and modes of adhesion measurement test do affect adhesion and failure behavior. In the case of bonded interactions, the mechanism of covalent silane bond formation through condensation and hydrolysis process is reviewed, and surface reactivity, molecular density, and adhesion properties are calculated with an example of silane functionalized polymer. Besides interfacial interactions, effects of external conditions, such as surface morphology of the glass substrate and relative humidity on the adhesion and failure behavior, are presented, and modeling techniques developed for building interfacial system and calculating adhesion strengths are briefly introduced.

The lattice Boltzmann method (LBM) is utilized to simulate the nanoscale flow physics of air bearings in the head-disk interface. In the high Knudsen number flow analysis of air bearings, the slip boundary model is very important to guarantee the accuracy of solution. In this paper, the Langmuir slip model for the rarefied gas flow was incorporated and its feasibility and accuracy was examined in nanoscale flow simulations. It was shown that our LBM can solve the fluid flow of air bearing with high efficiency due to its complex geometry handling capability and high accuracy comparable to the Boltzmann transport equation in the slip flow regime. The LBM model developed in this paper could serve as a powerful tool for the design of advanced air-bearing systems

Highly ordered mesoporous titania films were synthesized within a short time period by controlling the pH of sols and moisture exposure of as-prepared films.

The effect of nanoscale roughness on the adhesion between glassy silica and polyimides is examined by molecular dynamics simulation. Different silica surfaces, with varying degrees of roughness, were generated by cleaving bulk structures with a predefined surface and a desired average roughness, with different roughness periods and hydroxylation densities in an effort to study the influence of these surface characteristics on adhesion at the silica–polyimide interface. The calculated results reveal that average roughness Ra is the primary controlling factor within the considered conditions. Further, an energy decomposition analysis of the pulling process suggests that hydrogen bonding contributes to the adhesion on all the rough surfaces, while the Coulombic energy contribution becomes significant at higher Ra. From a structural analysis of the vacant volume and surface area, it is shown that the periodicity of roughness provides a rather interesting trend for the adhesion energy. Adhesion can increase with a reduction in period due to the corresponding surface area expansion; however, if vacant volumes exist at the interface, the level of adhesion can decrease. Competition between two opposing tendencies leads to the maximum adhesion, and hence, both Ra and period are key parameters to control the adhesion in nanoscale roughness.

We investigate two types of internal light-extraction layer structures for organic light-emitting diodes (OLEDs) that consist of silica nanoparticles (NPs) embedded in high-refractive-index TiO₂ matrices. The composite of silica NPs and TiO₂ matrices was coated on the glass substrate and fabricated with and without a SiO₂ planarization layer. An increase in the optical out-coupling efficiency by a factor of 2.0 was obtained at a high luminance of 3,000 cd/m² from OLEDs containing the silica NPs embedded in TiO₂ matrices between glass substrates and Zn-doped In₂O₃ (IZO) electrodes after additional planarization processes. This is consistent with the analytical result using the finite-difference time-domain (FDTD) method. Randomly distributed silica NPs acting as scattering centers could reduce the optical loss when extracting light. By using additional planarization processes with a PECVD-derived SiO₂ layer, one can assure that smoother surfaces provide higher out-coupling efficiency, which attain 100% and 97% enhancements in power (lm/W) and current (cd/A) efficiencies, respectively.