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Thermal analysis and Fourier transform infrared spectroscopy were used to investigate the thermal stability of two low-dielectric constant (Dk)/dielectric loss (Df) inks based on polyurethane acrylate. According to Arrhenius law, the Flynn–Wall–Ozawa method was used to calculate the apparent activation energy (as the standard apparent activation energy E0) of the ink film at weight loss rates were 10, 50 and 70% for the evaluation of its thermal aging performance. Results show that the activation energy of the ink compounded with acrylic fluorocarbon resin and polyurethane acrylate is relatively high. The Aehar–Brindey–Sharp–Wend–Worth differential method was used to analyze the most probable mechanism function of the ink film layer. The first, second, and third segments of the thermal decomposition temperature of the ink film are speculated to range from 126 to 247°C, from 247 to 384°C (follows the 3d diffusion model, and from 384 to 508°C (third-order chemical reaction), respectively. This article provides theoretical reference for the formulation design of 5G ink from the perspective of thermal decomposition mechanism and thermal stability.

To investigate the effect of kaolin particles on the flotation performance and froth stability of different particle sizes of bastnaesite, batch flotation tests and froth stability experiments were performed. The results demonstrated that poor froth stability of the coarse particle size bastnaesite led to poor flotation recovery. The medium particle size led to appropriate froth stability and also improved the recovery of bastnaesite. The fine particle size yielded an excessively stable froth, yet did not increase the adherence of bastnaesite particles to the bubbles, but it may have increased the entrainment of kaolin. A longer flotation time may have contributed to improving the recovery of the fine size fraction bastnaesite due to its greater flotation rate. Yet, it had little impact on the recovery of the coarse-grained bastnaesite. In addition, a low proportion (20%) of kaolin improved the recovery and flotation rate of the coarse size fraction bastnaesite. In general, however, the presence of kaolin was detrimental to the flotation performance of bastnaesite. Moreover, the presence of kaolin increased the froth stability of the bastnaesite and resulted in more hydrophilic kaolin particles being entrained into the concentrate products.

The anomalous Hall effect (AHE), and magnetic and electronic transport properties were investigated in a series of amorphous transition metal thin films---${\mathrm{Fe}}_{x}{\mathrm{Si}}_{1--x}, {\mathrm{Fe}}_{x}{\mathrm{Ge}}_{1--x}, {\mathrm{Co}}_{x}{\mathrm{Ge}}_{1--x}, {\mathrm{Co}}_{x}{\mathrm{Si}}_{1--x}$, and ${\mathrm{Fe}}_{1--y}{\mathrm{Co}}_{y}\mathrm{Si}$. The experimental results are compared with density functional theory calculations of the density of Berry curvature and intrinsic anomalous Hall conductivity. In all samples, the longitudinal conductivity (${\ensuremath{\sigma}}_{xx}$), magnetization ($M$), and Hall resistivity (${\ensuremath{\rho}}_{xy}$) increase with increasing transition metal concentration; due to the structural disorder ${\ensuremath{\sigma}}_{xx}$ is lower in all samples than a typical crystalline metal. In the systems with Fe as the transition metal (including ${\mathrm{Fe}}_{1--y}{\mathrm{Co}}_{y}\mathrm{Si}$), the magnetization and AHE are large and in some cases greater than the crystalline analog. In all samples, the AHE is dominated by the intrinsic mechanism, arising from a nonzero, locally derived Berry curvature. The anomalous Hall angle (AHA) $(={\ensuremath{\sigma}}_{xy}/{\ensuremath{\sigma}}_{xx})$ is as large as 5% at low temperature. These results are compared with the AHAs reported in a broad range of crystalline and amorphous materials. Previous work has shown that in a typical crystalline ferromagnet the Hall conductivity (${\ensuremath{\sigma}}_{xy}$) and ${\ensuremath{\sigma}}_{xx}$ are correlated and are usually either both large or both small, resulting in an AHA that decreases with increasing ${\ensuremath{\sigma}}_{xy}$. By contrast, the AHA increases linearly with increasing ${\ensuremath{\sigma}}_{xy}$ in the amorphous systems. This trend is attributed to a generally low ${\ensuremath{\sigma}}_{xx}$, while ${\ensuremath{\sigma}}_{xy}$ varies and can be large. In the amorphous systems, ${\ensuremath{\sigma}}_{xx}$ and ${\ensuremath{\sigma}}_{xy}$ are not coupled, and there may thus exist the potential to further increase the AHA by increasing ${\ensuremath{\sigma}}_{xy}$.

MCrAlY–Al2O3 composite coatings were prepared by high-velocity oxygen fuel thermal spraying with bespoke composite powder feedstock for high-temperature applications. Powder processing via a suspension route was employed to achieve a fine dispersion of α-Al2O3 submicron particles on the MCrAlY powder surface. This was, however, compromised by ~ 50% less flowability of the feedstock during spraying. Nevertheless, the novel powder manufacturing process introduced in this study has shown potential as an alternative route to prepare tailored composite powder feedstock for the production of metal matrix composites. In addition, the newly developed MCrAlY–Al2O3 composite coatings exhibited superior oxidation resistance, compared to conventional MCrAlY coatings, with the formation of nearly exclusively Al2O3 scale after isothermal oxidation at 900 °C for 10 h. The addition of α-Al2O3 particles in the MCrAlY coatings as a second phase was found to have promoted the formation of YAG oxides (YxAlyOz) during spraying and also accelerated the outwards diffusion of Al, which resulted in enhanced oxidation resistance.

To combat the high temperature chlorine-induced corrosion of materials in the biomass and waste fuel-fired thermal power plants NiCr coatings can be used. In this study, a commercially available Ni50Cr gas atomised powder was sprayed onto a power plant alloy using a liquid fuelled and a gas fuelled high velocity oxygen fuel thermal spray (HVOF), cold gas dynamic spray (CS) and laser cladding (LC). High temperature corrosion test was performed at 700 °C in a controlled environment corrosion test with 500 ppm HCl, 5 vol% O2 and bal. N2 for 250 h. KCl was deposited onto certain samples to understand the mechanism of high temperature chlorine-induced corrosion. The corrosion products were characterised in a SEM with EDX and XRD. A wide range of oxide morphology and distribution was found on the coating top surface which was primarily due to their processing techniques. Cross-section examination of the coatings showed various degrees of internal attack and scale growth. In the absence of any deposit on the surface, cold-sprayed coating showed the poorest performance since the corrosive ion penetrated ~600 μm after 250 h exposure, which is due to the inter-connected porosity. In presence of KCl deposit, laser cladded coating showed the best corrosion performance because the grooving pattern (traces of corrosive ion penetration) only penetrated 80 μm, which is predominantly due to its pore free microstructure.

A fully-transparent graphene-based charge-trap memory device was realized by fabricating a graphene-channel field-effect transistor with high-k/low-k/high-k oxide stacks of Al2O3/AlOx/Al2O3 and indium-tin-oxide gate/source/drain electrodes on the polyethylene naphthalate substrate (i.e., ITO-gated AXA-gFET). The usage of low-k AlOx as a charge-trap layer allowed us to demonstrate a high-performance memory device, exhibiting a large memory window of ∼9.2 V and a tenacious retention of the memory window margin up to ∼57% after 10 years. Memory cells comprising the ITO-gated AXA-gFET arrays displayed a high transparency with the average optical transmittance of ∼83% in visible wavelength regions. These properties may move us a step closer to the practical application of graphene-based memories for future transparent electronics. In-depth analyses on the electrical characteristics and the mechanisms of the memory functions are presented.

Gapless interdigitated back contact (IBC) solar cells were fabricated with phosphorous back surface field on a boron emitter, using an ion implantation process. Boron emitter (boron ion implantation) is counter doped by the phosphorus back surface field (BSF) (phosphorus ion implantation) without gap. The gapless process step between the emitter and BSF was compared to existing IBC solar cell with gaps between emitters and BSFs obtained using diffusion processes. We optimized the doping process in the phosphorous BSF and boron emitter region, and the implied Voc and contact resistance relationship of the phosphorous and boron implantation dose in the counter doped region was analyzed. We confirmed the shunt resistance of the gapless IBC solar cells and the possibility of shunt behavior in gapless IBC solar cells. The highly doped counter doped BSF led to a controlled junction breakdown at high reverse bias voltages of around 7.5 V. After the doping region was optimized with the counter doped BSF and emitter, a large-area (5 inch pseudo square) gapless IBC solar cell with a power conversion efficiency of 22.9% was made.

Ni50Cr thermally sprayed coatings are widely used for high temperature oxidation and corrosion in thermal power plants. In this study, a commercially available gas atomised Ni50Cr powder was sprayed onto a power plant alloy (ASME P92) using both gas and liquid fuelled high velocity oxy-fuel (HVOF) thermal spray. Microstructures of the two coatings were examined using SEM-EDX, XRD, oxygen content analysis and mercury intrusion porosimeter. The gas fuelled coating had higher levels of oxygen content and porosity. Shorter term air oxidation tests (4 h) of the free-standing deposits in a thermogravimetric analyser (TGA) and longer term air oxidation tests (100 h) of the coated substrates were performed at 700 °C. The kinetics of oxidation and the oxidation products were characterized in detail in SEM/EDX and XRD. In both samples, oxides of various morphologies developed on top of the Ni50Cr coatings. Cr2O3 was the main oxidation product on the surface of the coatings along with a small amount of NiO and NiCr2O4. Rietveld analysis was performed on the XRD data to quantify the phase composition of the oxides on both Ni50Cr coatings and their evolution with exposure time.

In this paper, we briefly review our recent progress on development of core technologies for 2G HTS NMR/MRI magnets at Korea University. To outperform the current state-of-art NMR/MRI magnet systems, we have developed the following technologies: 1) a REBCO-REBCO superconducting joint for operation of persistent current mode; 2) partial and grease-insulation winding techniques for self-protection of the HTS magnets; 3) pre-shimming to reduce the screening-current-induced-field; and 4) optimization of multi-width winding to minimize conductor consumption and volume of the HTS magnets. The test results demonstrated the feasibility of employing the developed techniques to achieve ultra-high-field and LHe-free 2G NMR/MRI magnets possessing self-protecting feature.

High velocity oxy-fuel (HVOF) thermal spray process has shown obvious advantages over other surface hardening techniques when depositing WC-based layers, such as the laser cladding, electrodeposition and chemical/physical vapour deposition (CVD/PVD) methods, due to its versatility, survivability of hardening phase and low cost. HVOF thermal sprayed WC-based coatings are widely used in components that operate in harsh environments needing excellent sliding, fretting, abrasion and erosion resistance. WC-CrxCy-Ni coating shows better wear performance than the WC-Co-Cr coating at high temperature but inferior wear performance at room temperature at lower loads according to literature; however, the wear performance and relevant mechanisms of these two coatings under higher loads has not been reported. To fill this knowledge gap, wear testing of HVOF thermal sprayed WC-CrxCy-Ni and WC-Co-Cr coatings under high loads (96, 240 and 318 N) against a sintered WC-Co (6 mm diameter ball) counter-body was studied in this paper. For WC-CrxCy-Ni coating, decarburization of CrxCy rather than WC, took place during spraying. While the decarburization of WC to W2C occurred in the WC-Co-Cr coating. The major hardening phase (WC) dominated the wear performance of the coatings given its high hardness and small size, and Co also appeared to be a superior binder phase than Ni. At the maximum load, the specific wear rate of WC-CrxCy-Ni coating against WC-Co counter body was 17.92 × 10-7 mm3 N-1m-1, which is two times that of WC-Co-Cr coating (9.81 × 10-7 mm3 N-1m-1). The wear mechanisms for WC-CrxCy-Ni coatings included abrasion of the matrix, cracking of the secondary carbide phase and pulling out of WC particles. For WC-Co-Cr coatings, abrasion of the matrix was marginal, and cracking of the secondary carbide was not observed. The presence of CrxCy of lower hardness than the WC decreased the wear resistance of entire WC-based coating at room temperature, and improved oxidation resistance of WC at high temperatures due to the higher affinity of Cr to O. Hence, the secondary carbide hardening phase may be detrimental when considering the wear applications of HVOF thermal sprayed WC-based coatings.

A schottky barrier diode (SBD) without field plate was fabricated on a Si-doped N-Ga 2 O 3 drift layer, which was grown by halide vapor phase epitaxy (HVPE) on a heavily Sn-doped (001) $\beta-\text{Ga}_{2}\mathrm{O}_{3}$ substrate. The thickness and concentration of N-drift layer were $5 \mu \mathrm{m}$ and $3.8\times 10^{16}\text{cm}^{-3}$ , respectively. The reverse breakdown voltage (BV) and specific on-resistance $(R_{\text{on}})$ of the fabricated Ga203 SBD were 825 V and $3.5 \mathrm{m}\Omega\cdot \text{cm}^{2}$ , respectively, leading to a high Baliga figure-of-merit $(BV^{2}/R_{\text{on}})$ of 194.5 MW·cm−2. Besides, a high current on/off ratio of $4.2\times 10^{10}$ was obtained.

This study was carried out to investigate a influence of humidity variation (%) on the magnetic properties and the surface flaws in the fabrication of Fe-based Fe Si B amorphous alloy ribbon by Planar Flow Casting process. As a result, the size of the air pocket and the droplet which is observed in the contact surface and the free face of the amorphous alloy ribbon becomes large when the humidity increases and the size highly increases with the surface roughness at the same time. Especially, the surface roughness value which is made in the 65 % of the humidity is the lowest in the contact surface (Ra = 0.60 µm, Rz = 3.11 µm) and the free face (Ra = 0.47 µ m,z =3 .00µm). Also, in case of the soft magnetic property of the magnetic core which is made with the toroidal core of 23(OD)*20(ID)*20(H) size, in the sample of the amorphous alloy ribbon which is made in 65 % of the humidity, the most excellent value is gained as B (B ) = 1.055 T, H = 0.083 Oe, permeability = 1,197 and core loss = 0.276 W/kg.

Pulsed electric field (PEF) may cause irreversible damage to bio-membranes of microorganisms, as electromechanical stresses induced across their membranes can stretch and rupture these phospholipid bi-layers. Local heating is important for further understanding of the biological action of the externally applied electric field as typically the PEF treatment is considered to be a nonthermal process: any increase in the global temperature of the microbial liquid suspension during this process does not result in the thermal inactivation of microorganisms. This paper is aimed at investigation of the transient local heating and transient mechanical stresses across biomembranes of model microorganisms stressed with the external electric field using a model developed in COMSOL Multiphysics. The obtained results demonstrate that high-field impulses can result in the development of strong local electro-mechanical stresses across the membrane, and significant local over-heating of the membrane and the cell wall, as compared with the global temperature of the external suspension. These results and the developed model can help in further understanding the biological action of the impulsive electric fields, and in further development and optimisation of the PEF technology.

We report the fabrication of short-channel FinFETs on InGaAs-on-silicon wafers using the aspect ratio trapping (ART) technique. We demonstrate excellent short-channel control down to 20 nm gate length due to scaled fin width down to 9 nm and reduction of parasitic bipolar effect (PBE). PBE that plagues III-V NFETs with gate-all-around (GAA) or III-V-on-insulator (III-V-OI) structures can be significantly suppressed by optimized ART FinFET technology. We demonstrate record high on-current ION and low drain leakage current for short gate lengths in the 20–32 nm range for InGaAs-on-silicon NFETs.

Following the trend of electronic device miniaturization, on-chip integrated solid-state micro-supercapcaitors (MS) were fabricated based on vertically aligned carbon nanofibers (VACNFs) as electrode materials and polymeric gel electrolyte as the solid electrolyte. The VACNFs were grown at 390 °C and 550 °C temperature on interdigitated micro-patterns, where the dimensions of the digits were kept the same but the gap between the digits varied from 10-100 µm. A maximum capacitance of 1 mF/cm2 and 0.53mF/cm2 (combined footprint area of digits and gaps) were measured for devices with CNFs grown at 390 °C and 20 µm gap, for 550 °C and 10 µm gap, respectively. These capacitances are an order of magnitude higher than the one for solid dielectric based silicon trenches capacitors. The low temperature MS show an inverse capacitance relation with the gap size whereas high temperature shows random behavior. High characteristic frequencies at 45° phase angle are 114 Hz for 100 µm gap and 142 Hz 30 µm gap for 390 °C and 550 °C temperatures. A model for the interdigitated capacitors was developed and the results showed that by eliminating the current collector resistances the characteristic frequencies can be increased to 965 Hz and 866 Hz from 67 Hz and 127 Hz for 10 µm gap patterns for 390 °C and 550 °C temperatures. The entire fabrication was done using CMOS compatible processes thus enabling integration directly on active CMOS chip.

TiO2 photocatalytic materials were successfully synthesised via solid-state reaction. Dehydrate titanyl sulfate (TiOSO4·2H2O) and sodium oxalate (Na2C2O4) powders were used as the reactants and polyethylene glycol (PEG-400) as the surface active agent, respectively. After grinding for 50 min at room temperature, the precursor (TiOC2O4) was prepared. The TiO2 photocatalytic materials were obtained by annealing the precursor in the temperature range of 300–800°C. The properties of the samples were characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmet–Teller (BET) methods. The photocatalytic performance of the samples was evaluated by degrading methyl orange (MO) under UV-light irradiation, with TiO2 prepared at 450°C showing the highest efficiency in the photodegradation process. The photocatalytic activity of the TiO2 photocatalytic materials was maintained after recycling five times.

Stripline kicker is an important component of both on-axis longitudinal accumulation [1] and on-axis swap out injection schemes in HALS (Hefei Advanced Light Source). After more than one year of R&D, construction of the first prototype is completed. The kicker performance is simulated. The results show that in the range of 0 ~ 1 GHz, on differential mode, S11 is less than - 20 dB. In order to facilitate installation, the extension part and PTEF bracket were designed. The assembly of kicker and commercial feedthrough has been tested with pulse generator and network analyzer.

TiC reinforced FeAl intermetallic matrix composite parts were successfully fabricated by selective laser melting using mechanically blended powders. Top surface and cross-sectional microstructure of FeAl/TiC and pure FeAl parts were observed by scanning electron microscopy and optical microscopy. The microhardness and modulus of elasticity were compared. The wear resistance of the melted parts was investigated, and the wear mechanisms were discussed based on worn surfaces and wear debris examinations. Results showed that TiC reinforced FeAl intermetallic matrix composite bulk parts present a relatively smooth and dense melted microstructure, and there are two phases in the composite part. Unmelted TiC reinforcements uniformly dispersed in the matrix. Compared with the pure FeAl parts, FeAl/TiC composite parts have a higher microhardness, an enhanced modulus of elasticity and a much better wear resistance, displaying much lower wear rate.

Defects play a crucial role in room temperature ferromagnetism of dilute magnetic semiconductors. Using valence electron energy-loss spectroscopy (EELS), it was found that the band gap of Co-doped ZnO was smaller than undoped ZnO and some mid-gap states appeared. Using core-loss EELS, the fine structures of the O K-edge exhibit material-specific defect features in the oxygen spectra. The EELS measurements with super high spatial resolution provide unambiguous indications that defects are presented in Co-doped ZnO nanostructures. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In-situ aberration-corrected transmission electron microscopy combined with density functional theory (DFT) calculations are employed to elucidate the electron beam induced dynamics of surface dislocations on ~ 4 nm × 6 nm sized Au (100) terraces located on top of hillock shaped Au at room temperature and 77 K at video rate (20 frames/s). At room temperature, very small terraces (

With the rapid development of nanotechnology in the past three decades, titanium dioxide (TiO 2 ) nanoparticles (NPs) are frequently used in consumer products, food additives, cosmetics, drug carriers, and so on. Once human beings are unintentionally exposed to NPs, they could be absorbed, and then accumulated in brain regions by passing through the blood–brain barrier or through the nose-to-brain pathway, potentially leading to dysfunctions of brain. Besides, NPs may affect brain development of the embryo by crossing the placental barrier. Several in vivo and in vitro researches have demonstrated that the morphology and function of neuronal or glial cells could be impaired by TiO 2 NPs, which might induce cell necrosis. The recognition ability, spatial memory, and learning ability of TiO 2 NP-treated rodents were significantly impaired, which meant that accumulation of TiO 2 NPs in the brain could lead to neurodegeneration. However, data obtained from those studies were not consistent as researchers may choose different experimental parameters, including administration ways, dosage, size, and crystal structure of TiO 2 NPs. In this chapter, we discuss how TiO 2 NPs interact with the brain.

This paper presents our recent progress on core technology development for a megawatt-class superconducting wind turbine generator supported by the international collaborative RD program of the Korea Institute of Energy Technology Evaluation and Planning. To outperform the current high-temperature-superconducting (HTS) magnet technology in the wind turbine industry, a novel no-insulation winding technique was first proposed to develop the second-generation HTS racetrack coil for rotating applications. Here, we briefly report our recent studies on no-insulation (NI) winding technique for GdBCO coated conductor racetrack coils in the following areas: (1) Charging-discharging characteristics of no-insulation GdBCO racetrack coils with respect to external pressures applied to straight sections; (2) thermal and electrical stabilities of no-insulation GdBCO racetrack coils encapsulated with various impregnating materials; (3) quench behaviors of no-insulation racetrack coils wound with GdBCO conductor possessing various lamination layers; (4) electromagnetic characteristics of no-insulation GdBCO racetrack coils under time-varying field conditions. Test results confirmed that this novel NI winding technique was highly promising. It could provide development of a compact, mechanically dense, and self-protecting GdBCO magnet for use in real-world superconducting wind turbine generators.

We designed and fabricated the AlGaN/GaN HFETs with step graded heterostructure in this work. Compared with the AlGaN/GaN HFETs with linearly graded layer, the AlGaN/GaN HFETs with step graded layer exhibited similar device performance, including the notable wide flat transconductance characteristics. For the AlGaN/GaN step graded heterostructure, each step layer is individual and can be controlled separately during the epi-growth. Especially for the uniformity optimization, the individual growth mode for the AlGaN/GaN step graded heterostructure guarantee the targeted optimization for each layer. It is hoped that this step-graded structure would promote the industrialization of GaN devices in wireless communications applications.

The increasing use of biomass as a fuel is leading to higher fireside corrosion of the heat exchangers in boilers due to the high chlorine and alkali metal content in the fuel. Laser cladding of Ni50Cr is a promising technique to enhance fireside corrosion resistance of boiler tubes from this aggressive environment. A parametric study is carried out on the blown powder based laser cladding of Ni50Cr on 304 stainless steel. Successful deposits were generated and the effects of the various process parameters on clad geometry and dilution are reported. The various commonly used techniques for determination of clad dilution are compared and some guidelines for their use are suggested.

Ultra-thin AlN/GaN heterostructure field-effect transistors (HFETs) with, and without, SiN passivation were fabricated by the same growth and device processes. Based on the measured DC characteristics, including the capacitance-voltage (C-V) and output current-voltage (I-V) curves, the variation of electron mobility with gate bias was found to be quite different for devices with, and without, SiN passivation. Although the AlN barrier layer is ultra thin (c. 3 nm), it was proved that SiN passivation induces no additional tensile stress and has no significant influence on the piezoelectric polarization of the AlN layer using Hall and Raman measurements. The SiN passivation was found to affect the surface properties, thereby increasing the electron density of the two-dimensional electron gas (2DEG) under the access region. The higher electron density in the access region after SiN passivation enhanced the electrostatic screening for the non-uniform distributed polarization charges, meaning that the polarization Coulomb field scattering has a weaker effect on the electron drift mobility in AlN/GaN-based devices.

This paper presents results, experimental and analytical, of the electrical characteristics of GdBCO single-pancake coils co-wound with a brass tape as metallic insulation (MI coil). The GdBCO pancakes were subjected to sudden discharge, charge-discharge, and over-current tests. The sudden discharge and charge-discharge test results of the MI coil demonstrated that MI coils can be charged and discharged significantly faster than non-insulated coils that are wound only with GdBCO tape. In over-current tests at 150 A (1.25I(c)), the MI coil exhibited better electrical behavior, i.e., self-protecting features, than its counterpart co-wound with Kapton tape, an insulator. Moreover, the experimental and analytical results are in agreement, validating the use of a concise equivalent parallel-RL circuit model for the MI coil to characterize its electrical behavior. Overall, the MI winding technique is highly promising to help build compact, mechanically robust, and self-protecting magnets composed of REBCO pancake coils. With no organic material in the winding, MI REBCO pancakes will be immune to neutron radiation damage, making the MI winding technique a viable option for fusion reactors, such as for toroidal field, poroidal field magnets, and central solenoid.

Electrical stress and 10-keV x-ray and 1.8-MeV proton irradiation and annealing responses are evaluated for graphene-based non-volatile memory devices. The memory characteristics of these structures derive primarily from hysteretic charge exchange between the graphene and interface and border traps, similar to the operation of metal-nitride-oxide-semiconductor memory devices. Excellent stability and memory retention are observed for ionizing radiation exposure or constant-voltage stress. Cycling of the memory state leads to a significant reduction in memory window.

Single tracks of selective laser melted FeAl intermetallics were studied in this paper in order to manufacture a perfect part. The morphology evolution of single tracks with the variation in laser scanning speed was analysed, and the bottom heating of substrate or premelted layer was proposed to obtain a better flattening degree of molten FeAl droplets. Reasonable mechanisms for morphology evolution were provided. It is revealed that with increasing the laser scanning speed, the surface tension gradient plays an important role in morphology evolution, while the bottom heating of substrate or premelted layer can counteract the contraction effect of FeAl particles induced by laser scanning speed.

Graphene-based non-volatile charge-trap memory devices were fabricated and characterized to investigate the implementation effect of both 2-dimensional graphene and the 3-dimensional memory structure. The single-layer-graphene (SLG) channel devices exhibit larger memory windows compared to the multi-layer-graphene (MLG) channel devices. This originates from the gate-coupling strength being larger in SLG devices than in MLG devices. Namely, the electrostatic charge screening effect becomes enhanced upon increasing the number of graphene layers; therefore, the gate tunability is reduced in MLG compared to SLG. The results suggest that SLG is more desirable for memory applications than MLG.

Viscoelastic behavior has a remarkable impact on the functional realization of shape memory polymers and their composites. Our previous work reported that a series of shape memory epoxies with varied curing agents and contents were synthesized and exhibited higher shape fixture and recovery rates. The viscoelastic behavior of the materials at different temperatures is experimentally investigated in this study. Stress–strain hysteresis under uniaxial tension, stress relaxation, and creep tests are performed. The energy dissipation factor and residual strain factor as functions of temperatures are presented in the basis of stress–strain hysteresis tests. Moreover, the effects of test temperature, curing-agent type, and content on the viscoelastic behavior of these materials are discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Dry ice blasting, as an environmentally–friendly method, was used during atmospheric plasma spraying for improving coating properties. This process is believed to be capable of reducing the porosity and the oxide of the coating and increasing the deposition efficiency, etc. Considering dry ice pellets are carried and accelerated by compressed air through a convergent–divergent nozzle, the computational fluid dynamic approach was first employed in this study to evaluate the effects of nozzle geometry, accelerating gas conditions as well as properties of pellets, on the pellet velocity variation and further to optimise the process. Moreover, the experiment with a steel powder was then carried out and the results indicate that a denser coating with a lower content of oxide can be achieved with the application of dry ice blasting during the plasma spraying.

A new cryogen, a mixture of solid argon and a small amount of liquid nitrogen, was studied to improve thermal contact between the solid cryogen and high-temperature superconducting tapes. A feasibility study of the reference design codes and the thermal requirements was conducted to optimize the design of the mixed cryogen cooling system. Experimental results showed that thermal and electrical stabilities of YBCO coated conductor tapes were significantly improved when they were impregnated with the mixed cryogen. Dry-out problems were overcome by the mixed cryogen because the small amount of liquid nitrogen improved thermal contact between the solid cryogen and superconducting tape.

Quench tests of a GdBCO racetrack pancake coil were conducted in liquid nitrogen at 77 K. Minimum quench energy and two-dimensional normal zone propagation velocities of the coil are discussed. Longitudinal normal zone propagation velocities in the curved section were almost twice those in the straight portion due to stress effects, showing that protection of the straight portion is of greater importance than protection of the curved portion when using racetrack-type, GdBCO pancake coils in large-scale rotating machines.

The thermodynamic behavior of excitonic emission properties in manganese- and zinc-codoped indium phosphide (InMnP:Zn) diluted magnetic semiconductor (DMS) layers was investigated. Compared to the InMnP:Zn DMS layer (Mn ≈ 0.06%), the inhomogeneous thermal-broadening of the excitonic-emission line-width in InMnP:Zn DMS layer (Mn ≈ 0.29%) is dominant at lower temperatures. This is attributed to the increase of ionized impurity scattering from Mn ions and results in the increase of exciton–phonon coupling strength. As a consequence, high Mn content can lead to low excitonic emission efficiency, although generally a larger Mn content is favorable to increase the Curie temperature of a DMS material.

Bilayer graphene has recently earned great attention for its unique electronic properties and commendable use in electronic applications. Here, we report the observation of quantum dot (QD) behaviors in bilayer graphene nanoribbons (BL-GNRs). The periodic Coulomb oscillations indicate the formation of a single quantum dot within the BL-GNR because of the broad distribution function of the carrier concentration fluctuation at the charge neutrality point. The size of the QD changes as we modulate the relative position between the Fermi level and surface potential. Furthermore, the potential barriers forming the QD remain stable at elevated temperatures and external bias. In combination with the observation of transport gaps, our results suggest that the disordered surface potential creates QDs along the ribbon and governs the electronic transport properties in BL-GNRs.

The stability issue of high temperature superconducting (HTS) racetrack coils is one of the most important factors for the development of large-scale rotating machines, such as ship propulsion motors and power generators. However, The stability and normal zone propagation characteristics of HTS racetrack pancake (RP) coils are not sufficient yet. In this study, quench tests for a GdBCO racetrack pancake coil were carried out under the condition of at 77 K. Minimum quench energy and two-dimensional normal zone propagation velocities of the coil are also discussed. Normal zone propagation velocity in the coil`s curved section is faster than in its straight section due to stress effects. The test results show that the protection of the straight section is of greater importance than that of the curved section when GdBCO racetrack pancake coils are applied to large-scale rotating machines.

Graphene's single atomic layer of sp(2) carbon has recently garnered much attention for its potential use in electronic applications. Here, we report a memory application for graphene, which we call graphene flash memory (GFM). GFM has the potential to exceed the performance of current flash memory technology by utilizing the intrinsic properties of graphene, such as high density of states, high work function, and low dimensionality. To this end, we have grown large-area graphene sheets by chemical vapor deposition and integrated them into a floating gate structure. GFM displays a wide memory window of ∼6 V at significantly low program/erase voltages of ±7 V. GFM also shows a long retention time of more than 10 years at room temperature. Additionally, simulations suggest that GFM suffers very little from cell-to-cell interference, potentially enabling scaling down far beyond current state-of-the-art flash memory devices.

Quench protection is one of the most important issues for magnet applications using 2 G HTS tapes because of their non-self-protecting properties. Although many researchers have examined the quench/recovery characteristics of HTS magnets to establish the required stability, new information on the quench/recovery characteristics of the recently commercialized HTS magnet with GdBCO CC is needed. In this study, the quench/recovery characteristics of Zr-doped (Gd,Y)BCO CC pancake coils that were insulated with various materials, such as copper and Kapton tapes, were examined in a liquid nitrogen (LN2) bath. The minimum quench energy (MQE) and normal zone propagation (NZP) velocity of the Zr-doped (Gd,Y)BCO CC pancake coils are discussed in terms of the quench/recovery test results.

Recently, a cooling system using solid nitrogen (SN2) as a cryogen was suggested to enhance the thermal and electrical stabilities of high temperature superconductor (HTS) magnet applications, due to its large heat capacity. For the successful application of the SN2 cooling system to HTS devices, it is necessary to obtain sufficient data about the thermal and electrical characteristics of the SN2-cooled YBCO coated conductor (CC). Therefore, this study examined the thermal and electrical properties of YBCO CC tapes with different stabilizers in the presence and absence of SN2. The results clearly showed that the thermal and electrical stabilities of the YBCO CC tapes were drastically improved in the presence of the SN2, regardless of the stabilizer materials. Furthermore, copper was found to be more suitable as a stabilizer of YBCO CC tape in the SN2 cooling system than stainless steel.

The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with graphene's perfect carbon honeycomb lattice. Our observations suggest that growth models including a stagnant catalytic surface do not apply to graphene growth on copper. Contrary to current expectations, these results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure.

This paper presents corrosion failure analysis on a commercial pure nickel thermocouple sheath used in BaTiO(3) hydrothermal synthesis reactor. Detailed investigations of the corrosion products have been performed using stereomicroscope, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was found that the corrosion failure of the sheath was mainly due to general corrosion and crevice corrosion of pure nickel, and the main corrosion products were Ni(OH)(2). Many cracks were observed inside the corrosion products and along the interfaces between the corrosion products and metal matrix. BaTiO(3) particles were deposited as parallel white bands along the above cracks inside the corrosion products. Chloride ions also entered the cracks or crevices, resulting in the acidification inside the crevice and aggravated the attack of nickel matrix. Some recommendations to prevent/minimize future similar corrosion failures were proposed. (C) 2010 Elsevier Ltd. All rights reserved.

In this work, a Wheatstone bridge-type pressure sensor based on AlGaN/GaN heterostructure was fabricated for the first time. The pressure sensor consisted of four gateless high electron mobility transistors (HEMTs) on a 585 μm depth circular membrane, in which 15-μm-thick silicon substrate was left. Direct voltage readout was realized in the AlGaN/GaN pressure sensor, which exhibited a non-linearity of 0.6% with a sensitivity of 1.25 μV/kPa/V over a wide pressure range from 0.1 MPa to 5 MPa. Because of the in-plane isotropic properties, the working mechanism in the AlGaN/GaN pressure sensor is found to be quite different from the silicon-based sensor. Although the resistances of the four gateless HEMTs all increased with enlarging pressure, the changes of neighboring resistors varied with alignments under the piezoelectric effects. Finally, voltage linear readout was realized by the differential operation of Wheatstone bridge circuit.

In the paper, we report one-step synthesis of novel wurtzite-structured ZnS three dimensional architectures assembled from thin nanorods in mixed solvent of ethylenediamine (en) and ethylene glycol, and wurtzite ZnS nanorods in a pure en solvent, both adopting Zn(CH(3)COO)(2)center dot 2H(2)O and (NH(2))(2)CS as raw materials. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction were applied to characterize the samples. It was found that the volume ratio of solvents and the concentration of (NH(2))(2)CS played important roles in the formation of wurtzite-structured ZnS nanorods, and the thin wurtzite ZnS nanorods with mean diameter of 6 nm were successfully synthesized. The optical absorption edges of the thin ZnS nanorods were found to be blue-shifted compared with that of the bulk ZnS due to the quantum confinement effect.

The compressive response of an alumina-filled epoxy composite material was characterized at various strain rates using a Kolsky bar and universal testing frame (MTS). In the Kolsky-bar experiments, dynamic stress equilibrium and constant strain-rate deformation in specimens were achieved using pulse-shaping techniques. The effects of specimen aspect ratio and interfacial friction on the dynamic response of the material were examined. Compressive stress-strain curves for the composite were obtained at strain rates ranging from 9.4 × 10-4 to 1.35 × 103 s-1 which exhibited strong strain-rate sensitivity. A material response model, which agrees well with the experimental measurements for the strain rates examined in this study, is also described.

This work investigates the environmental impacts of three manufacturing processes for a promising biodegradable polymeric material: polyhydroxyalkanoate (PHA). The processes studied are microbial PHA manufacturing using glucose as the carbon substrate, microbial PHA manufacturing using cheese whey as the carbon substrate, and microbial PHA manufacturing using genetically engineered plants. A lifecycle model is established for each of the processes, and the Eco-indicator 99 methodology is used in the study. Results with 10 indicators under human health, ecosystem quality, and resources are obtained and compared. Because the processes are still largely under development, many lifecycle data are rare and insufficient. A number of reference sources and reasonable assumptions are used in the calculations. The study has identified the major contributors to environmental impacts, and can quantitatively explain how each impact indicator is affected by a particular process. The study provides the information for t...

In this study, we developed a long split Hopkinson pressure bar (LSHPB) for mechanically characterizing soft materials at intermediate strain rates. Using a proper pulse shaper, a loading pulse over 3 ms was produced for compression experiments on a PMDI foam material at the strain rates in the order of 10/s. The pulse shaping technique minimized the dispersion effects of stress wave when propagating through such a long bar system. Consistency of stress–strain curves obtained from the LSHPB and an MTS in the same strain rate range shows that a gap currently existing in intermediate strain-rate range is closed by the introduction of the LSHPB.

In a dynamic experiment to obtain the high-rate stress–strain response of a ductile specimen, it takes a finite amount of time for the strain rate in the specimen to increase from zero to a desired level. The strain in the specimen accumulates during this strain-rate ramping time. If the desired strain rate is high, the specimen may yield before the desired rate is attained. In this case, the strain rates at yielding and early plastic flow are lower than the desired value, leading to inaccurate determination of the yield strength. Through experimentation and analysis, we examined the validity and accuracy of the flow stresses for ductile materials in a split Hopkinson pressure (SHPB) bar experiment. The upper strain-rate limit for determining the dynamic yield strength of ductile materials with a SHPB is identified.

Extrusion-spheronisation was used to generate smooth, highly spherical granules of a microcrystalline cellulose/propyl gallate/water paste. Freeze-drying retained the shape and size of the granules, whereas oven-drying produced roughened granules due to the uneven shrinkage of the wet powders. Compaction of one size fraction indicated that the granule strength differed noticeably, with the oven-dried samples producing tablets of lower voidage for a given applied compaction pressure. There was a reasonable correlation between tablet crushing strength and voidage. Major differences were observed in tablet dissolution, with the freeze-dried material exhibiting a two-regime behaviour and an initial dissolution rate constant an order of magnitude greater than the oven-dried form. Both the voidage and dissolution characteristics are postulated to be determined by the microstructure established during drying.