Showing papers on "FOIL method published in 2015"

Synthesis of large-area multilayer hexagonal boron nitride for high material performance

Abstract: Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young’s modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ∼24,000 cm2 V−1 s−1 at room temperature, higher than that (∼13,000 2 V−1 s−1) with exfoliated h-BN. By placing additional h-BN on a SiO2/Si substrate for a MoS2 (WSe2) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times. Multilayer h-BN films are highly desired for various applications in 2D nanoelectronics. Here, the authors demonstrate the synthesis of large-area and high-quality multi-layer h-BN films on Fe foil with high 2D material performance.

Synthesis of large-area multilayer hexagonal boron nitride for high material performance

Abstract: Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young’s modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ∼24,000 cm2 V−1 s−1 at room temperature, higher than that (∼13,000 2 V−1 s−1) with exfoliated h-BN. By placing additional h-BN on a SiO2/Si substrate for a MoS2 (WSe2) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times. Multilayer h-BN films are highly desired for various applications in 2D nanoelectronics. Here, the authors demonstrate the synthesis of large-area and high-quality multi-layer h-BN films on Fe foil with high 2D material performance.

Synthesis of centimeter-scale monolayer tungsten disulfide film on gold foils

Abstract: We report the synthesis of centimeter-scale monolayer WS2 on gold foil by chemical vapor deposition. The limited tungsten and sulfur solubility in gold foil allows monolayer WS2 film growth on gold surface. To ensure the coverage uniformity of monolayer WS2 film, the tungsten source-coated substrate was placed in parallel with Au foil under hydrogen sulfide atmosphere. The high growth temperature near 935 °C helps to increase a domain size up to 420 μm. Gold foil is reused for the repeatable growth after bubbling transfer. The WS2-based field effect transistor reveals an electron mobility of 20 cm2 V–1 s–1 with high on–off ratio of ∼108 at room temperature, which is the highest reported value from previous reports of CVD-grown WS2 samples. The on–off ratio of integrated multiple FETs on the large area WS2 film on SiO2 (300 nm)/Si substrate shows within the same order, implying reasonable uniformity of WS2 FET device characteristics over a large area of 3 × 1.5 cm2.

High-speed roll-to-roll manufacturing of graphene using a concentric tube CVD reactor

Abstract: We present the design of a concentric tube (CT) reactor for roll-to-roll chemical vapor deposition (CVD) on flexible substrates, and its application to continuous production of graphene on copper foil. In the CTCVD reactor, the thin foil substrate is helically wrapped around the inner tube, and translates through the gap between the concentric tubes. We use a bench-scale prototype machine to synthesize graphene on copper substrates at translation speeds varying from 25 mm/min to 500 mm/min, and investigate the influence of process parameters on the uniformity and coverage of graphene on a continuously moving foil. At lower speeds, high-quality monolayer graphene is formed; at higher speeds, rapid nucleation of small graphene domains is observed, yet coalescence is prevented by the limited residence time in the CTCVD system. We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD. We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions. We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

Molybdenum Phosphosulfide: An Active, Acid‐Stable, Earth‐Abundant Catalyst for the Hydrogen Evolution Reaction.

Abstract: Surface-sulfur modified MoP catalyst is prepared by drop casting aliquots of 0.25 M (NH4)6Mo7O24 and (NH4)2HPO4 solutions on a Ti foil support followed by drying, thermal reduction (5% H2/N2, 650 °C, 2 h), and thermal sulfidation (10% H2S/H2, 400 °C, 15 min).

Self-induced flapping dynamics of a flexible inverted foil in a uniform flow

Abstract: We present a numerical study on the self-induced flapping dynamics of an inverted flexible foil in a uniform flow. A high-order coupled fluid–structure solver based on fully coupled Navier–Stokes and nonlinear structural dynamic equations has been employed. Unlike a conventional flexible foil flapping where the leading edge is clamped, the inverted elastic foil is fixed at the trailing edge and the leading edge is allowed to oscillate freely. We investigate the evolution of flapping instability of an inverted foil as a function of the non-dimensional bending rigidity, , Reynolds number, , and structure-to-fluid mass ratio, , and identify three distinct stability regimes, namely (i) fixed-point stable, (ii) deformed steady and (iii) unsteady flapping state. With the aid of a simplified analytical model, we show that the fixed-point stable regime loses its stability by static-divergence instability. The transition from the deformed steady state to the unsteady flapping regime is marked by a flow separation at the leading edge. We also show that an inverted foil is more vulnerable to static divergence than a conventional foil. Three distinct unsteady flapping modes have been observed as a function of decreasing : (i) inverted limit-cycle oscillations, (ii) deformed flapping and (iii) flipped flapping. We characterize the transition to the deformed-flapping regime through a quasistatic equilibrium analysis between the structural restoring and the fluid forces. We further examine the effects of on the post-critical flapping dynamics at a fixed . Finally, we present the net work done by the fluid and the bending strain energy developed in a flexible foil due to the flapping motion. For small , we demonstrate that the flapping of an inverted flexible foil can generate times more strain energy in comparison to a conventional flexible foil flapping, which has a profound impact on energy harvesting devices.

In situ synthesis of a NiS/Ni3S2 nanorod composite array on Ni foil as a FTO-free counter electrode for dye-sensitized solar cells

Abstract: A NiS/Ni3S2 nanorod composite array that directly grows on Ni foil has been used as a counter electrode for dye-sensitized solar cells; these nickel sulfide nanorods exhibit excellent photo-electrical conversion efficiency when compared with conventional noble-metal Pt electrodes.

Facile growth of centimeter-sized single-crystal graphene on copper foil at atmospheric pressure

Abstract: By mildly oxidizing Cu foil and slowing down the total gas flow rate, we develop an easily repeatable atmospheric growth method to grow single-crystal graphene of centimeter-size. The graphene edge, which is different from the previously reported straight edge, is connected by a series of graphene-corners. The graphene-corner, ranging between 100° and 110°, is formed by a zig-zag edge and a mix edge. The oxidation of Cu crystal boundaries results in the rearrangement of active Cu sites for graphene nucleation, thus suppressing graphene nucleation density.

TiO2 Nanotube Array Photoelectrocatalyst and Ni–Sb–SnO2 Electrocatalyst Bifacial Electrodes: A New Type of Bifunctional Hybrid Platform for Water Treatment

Abstract: Bifunctional hybrid electrodes capable of generating various reactive oxygen species (ROS) over a wide range of potentials were developed by coupling electrocatalysts and photoelectrocatalysts. To achieve this, Ni-doped Sb-SnO2 (NSS) was deposited on one side of a titanium (Ti) foil while the other side was anodized to grow a TiO2 nanotube array (TNA) for electrochemical ozone generation and photoelectrochemical hydroxyl radical generation, respectively. Surface characterization indicated that NSS and TNA were formed and spatially separated yet electrically connected through the Ti substrate. While each catalyst possessed unique electrochemical properties, the coupling of both catalysts resulted in mixed electrochemical properties that drove electrocatalysis at high potentials and photoelectrocatalysis at low potentials. The performance of the NSS/TNA electrode for phenol decomposition was ∼3 times greater than that of single-layer catalysts and ∼1.5 times greater than the combined catalytic performances ...

Numerical study on the power extraction performance of a flapping foil with a flexible tail

Abstract: The numerical study on the power extraction performance of a flapping foil with a flexible tail is performed in this work. A NACA0015 airfoil is arranged in a two-dimensional laminar flow and imposed with a synchronous harmonic plunge and pitch rotary motion. A flat plate that is attached to the trailing edge of the foil is utilized to model a tail, and so they are viewed as a whole for the purpose of power extraction. In addition, the tail either is rigid or can deform due to the exerted hydrodynamic forces. To implement numerical simulations, an immersed boundary-lattice Boltzmann method is employed. At a Reynolds number of 1100 and the position of the pitching axis at third chord, the influences of the mass and flexibility of the tail as well as the frequency of motion on the power extraction are systematically examined. It is found that compared to the foil with a rigid tail, the efficiency of power extraction for the foil with a deformable tail can be improved. Based on the numerical analysis, it is indicated that the enhanced plunging component of the power extraction, which is caused by the increased lift force, directly contributes to the efficiency improvement. Since a flexible tail with medium and high masses is not beneficial to the efficiency improvement, a flexible tail with low mass together with high flexibility is recommended in the flapping foil based power extraction system.

A deformation mechanism of hard metal surrounded by soft metal during roll forming

Abstract: It is interesting to imagine what would happen when a mixture of soft-boiled eggs and stones is deformed together. A foil made of pure Ti is stronger than that made of Cu. When a composite Cu/Ti foil deforms, the harder Ti will penetrate into the softer Cu in the convex shapes according to previously reported results. In this paper, we describe the fabrication of multilayer Cu/Ti foils by the roll bonding technique and report our observations. The experimental results lead us to propose a new deformation mechanism for a hard metal surrounded by a soft metal during rolling of a laminated foil, particularly when the thickness of hard metal foil (Ti, 25 μm) is much less than that of the soft metal foil (Cu, 300 μm). Transmission Electron Microscope (TEM) imaging results show that the hard metal penetrates into the soft metal in the form of concave protrusions. Finite element simulations of the rolling process of a Cu/Ti/Cu composite foil are described. Finally, we focus on an analysis of the deformation mechanism of Ti foils and its effects on grain refinement and propose a grain refinement mechanism from the inside to the outside of the laminates during rolling.

The nature of the brittle-to-ductile transition of ultra fine grained tungsten (W) foil

Abstract: The aim of this work is to answer the question of whether an ultra fine grained (UFG) microstructure has an impact on the nature of the brittle-to-ductile transition (BDT) of tungsten. Therefore, four-point bend tests were performed using unnotched 100 μm UFG tungsten foil and annealed coarse-grained polycrystalline tungsten foil (2073 K for 2 h in vacuum) with exactly the same chemical composition and dimensions. The reported results for coarse-grained tungsten foil show a strain-rate dependent BDT that occurs between 350 and 450 K. The activation energy of the BDT, E BDT , for the coarse-grained material was deduced to be 2.9 (+ 2.6/− 0.9) eV. The results obtained from UFG tungsten foil indicate a strain-rate independent BDT at relatively low temperatures (≈ 77 K). The strong disparity in the nature of the BDT can be attributed solely to the presence of microstructural differences. The possible mechanism controlling the BDT in tungsten for both tungsten foil conditions will be discussed against this background and in the light of previous studies performed on the nature of the BDT of tungsten reported in pertinent literature.

Growth kinetics of white graphene (h-BN) on a planarised Ni foil surface

Abstract: The morphology of the surface and the grain orientation of metal catalysts have been considered to be two important factors for the growth of white graphene (h-BN) by chemical vapour deposition (CVD). We report a correlation between the growth rate of h-BN and the orientation of the nickel grains. The surface of the nickel (Ni) foil was first polished by electrochemical polishing (ECP) and subsequently annealed in hydrogen at atmospheric pressure to suppress the effect of the surface morphology. Atmospheric annealing with hydrogen reduced the nucleation sites of h-BN, which induced a large crystal size mainly grown from the grain boundary with few other nucleation sites in the Ni foil. A higher growth rate was observed from the Ni grains that had the {110} or {100} orientation due to their higher surface energy.

Low defect concentration few-layer graphene using a two-step electrochemical exfoliation

Abstract: Low defect concentration few-layer graphene (FLG) sheets were fabricated by a two-step electrochemical intercalation exfoliation, including a graphite foil pretreatment in sodium hydroxide solution and a subsequent further exfoliation in sulfuric acid solution. During the process, the pretreatment results in the expansion of the graphite foil and in turn facilitates the final exfoliation in sulfuric acid solution. The results show that the ID/IG of the obtained FLG sheets is as low as 0.29 while maintaining relatively high yield, more than 56%. In addition, the oxygen content in the FLG sheets is 8.32% with the C/O ratio of 11.02.

Conductor connection member, connection structure, and solar cell module

Abstract: The electric conductor connecting member of this invention comprises a metal foil having a roughened surface on at least one main side, and an adhesive layer formed on the roughened surface of the metal foil.

Fabrication of a highly sensitive surface-enhanced Raman scattering substrate for monitoring the catalytic degradation of organic pollutants

Abstract: In this paper, we demonstrate a simple and reliable two-step strategy based on an electrospinning technique combined with in situ calcination for the fabrication of ZnO nanofibers deposited on a silver foil surface. These nanofibers are used as a novel sensitive surface-enhanced Raman scattering (SERS) substrate. The strong interactions between ZnO nanofibers and silver foil afford continuous delocalized surface plasmons, resulting in localization of the electric field at the gap between the ZnO nanofibers and silver foil; thus, the exciton–plasmon interactions between ZnO nanofibers and the silver foil surface contribute to the enhanced scattering, generating a large electromagnetic field enhancement. In addition, the ZnO nanofibers deposited on the silver foil surface exhibit enhanced photocatalytic activity toward the degradation of organic pollutants because of the charge separation effect and increase in the lifetime of the photogenerated excitons under ultraviolet light irradiation; thus, this new substrate can be used as a SERS substrate for determining the catalytic activity and reaction kinetics during the photodegradation of organic pollutants.

Carbon uptake during Spark Plasma Sintering: investigation through the analysis of the carbide “footprint” in a Ni–W alloy

Abstract: In the majority studies of materials produced by Spark Plasma Sintering (SPS), the powders are consolidated in graphite dies using graphite punches and protective graphite foil. As a result, carbon uptake by the sintered material can occur. In this study, a Ni–15 at% W alloy was studied in this context for the first time and was chosen as a suitable model system, in which tungsten forms stable carbides whereas nickel does not, but offers a medium for carbon diffusion into the interior of the compact. In a disk-shaped 3 mm-thick compact Spark Plasma Sintered at 900 °C, carbon uptake resulted in the formation of tungsten carbide WC particles ranging from 0.2 to 2 μm in the subsurface layers of the compact (within distances 50–100 μm from the interface with the foil). The size of the WC particles varied with distance, smaller particles forming in the vicinity of the interface—in the area in which the nucleation was favoured at high carbon concentrations. However, it was not only the subsurface layer that was affected by the presence of carbon: particles of Ni2W4C were found at depths greater than 100 μm from the interface and throughout the volume of the compact. The distribution of the submicron WC particles and particles of Ni2W4C corresponded to a network of boundaries between the agglomerates of the Ni–W powder that was consolidated into a compact. These boundaries offered paths for faster diffusion of carbon from the foil when compared with the volume of the agglomerates. The carbide subsurface layer dramatically changed the interdiffusion behaviour of the sintered material in a pair with aluminum due to a significantly reduced concentration of tungsten capable of diffusing within a metallic phase.

Experimental and theoretical analysis of a rigid rotor supported by air foil bearings

Abstract: The popularity of compressors utilizing foil bearings is increasing. Their mechanical design is challenging, and an accurate prediction of the bearing coefficients is important. A mathematical model taking into account the foil structure, and the detailed geometry of a three pad foil bearing are presented. The steady state solution and dynamic coefficients are obtained through zeroth and first order perturbed equations respectively. Analysis of the foil structure reveals the importance of distinguishing between a static foil stiffness for the zeroth order equation and a dynamic stiffness for the first order equation. Calculated bearing coefficients are compared to experimental results obtained from a dedicated test rig. Generally, good agreement is observed and minor discrepancies for the damping coefficients are discussed.

5 × 5 cm2 silicon photonic crystal slabs on glass and plastic foil exhibiting broadband absorption and high-intensity near-fields

Abstract: 5 × 5 cm 2 silicon photonic crystal slabs on glass and plastic foil exhibiting broadband absorption and high-intensity near-fields

Tungsten (W) Laminate Pipes for Innovative High Temperature Energy Conversion Systems

Abstract: The aim of this paper is to present the mechanical properties of tungsten laminate pipes made of tungsten foil and to discuss their use in innovative high temperature energy conversion systems. Tungsten is the metal with the highest melting point of all metals and would therefore be an excellent fit for high temperature applications. But tungsten has one major drawback which is its low fracture toughness at room temperature (RT) or its high brittle-to-ductile transition temperature (BDTT). However, one of the extraordinary properties of tungsten is that by cold working the BDTT can be shifted to lower temperatures. At the extreme, these results in a tungsten foil with a BDTT below −120 °C combined with an RT fracture toughness of 70 MPa m1/2. By rolling up and joining a tungsten foil, tungsten laminate pipes can be synthesized that can dissipate at least 20 J in a Charpy impact test at RT and survive a burst test at RT at 1000 bar without any residual damage. The technical maturity of these W laminate pipes is approved by high heat flux tests performed at the Plataforma Solar de Almeria, Spain, as well as at the Max Planck Institute of Plasma Physics, Garching, Germany.

Ultraclean and large-area monolayer hexagonal boron nitride on Cu foil using chemical vapor deposition.

Abstract: Atomically thin hexagonal boron nitride (h-BN) has been demonstrated to be an excellent dielectric layer as well as an ideal van der Waals epitaxial substrate for fabrication of twodimensional (2D) atomic layers and their vertical heterostructures. Although many groups have obtained large-scale monolayer h-BN through low pressure chemical vapor deposition (LPCVD), it is still a challenge to grow clean monolayers without the reduction of domain size. Here we report the synthesis of large-area (4×2 cm 2 ) high quality monolayer h-BN with an ultraclean and unbroken surface on copper foil by using LPCVD. A detailed investigation of the key factors affecting growth and transfer of the monolayer was carried out in order to eliminate the adverse effects of impurity particles. Furthermore, an optimized transfer approach allowed the nondestructive and clean transfer of the monolayer from copper foil onto an arbitrary substrate, including a flexible substrate, under mild conditions. Atomic force microscopy indicated that the root-mean-square (RMS) roughness of the monolayer h-BN on SiO2 was less than 0.269 nm for areas with fewer wrinkles. Selective area electron diffraction analysis of the h-BN revealed a pattern of hexagonal diffraction spots, which unambiguously demonstrated its highly crystalline character. Our work paves the way toward the use of ultraclean and large-area monolayer h-BN as the dielectric layer in the fabrication of high performance electronic and optoelectronic devices for novel 2D atomic layer materials. S Online supplementary data available from stacks.iop.org/NANO/26/275601/mmedia