Showing papers on "Fabrication published in 2014"

Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices

Abstract: Optical generation of hot electrons in metallic structures and its potential as an alternative to conventional electron–hole separation in semiconductor devices are reviewed. The possibilities for realizing high conversion efficiencies with low fabrication costs are discussed along with challenges in terms of the materials, architectures and fabrication methods

Method and apparatus for three-dimensional fabrication

Abstract: The present invention relates to methods and an apparatus for the fabrication of solid three-dimensional objects from liquid polymerizable materials.

Fabrication of Micro/Nano Structures on Metals by Femtosecond Laser Micromachining

Abstract: Femtosecond laser micromachining has emerged in recent years as a new technique for micro/nano structure fabrication because of its applicability to virtually all kinds of materials in an easy one-step process that is scalable. In the past, much research on femtosecond laser micromachining was carried out to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of surface structures because of their numerous possible applications. The state-of-the-art knowledge on the fabrication of these structures on metals with direct femtosecond laser micromachining is reviewed in this article. The effect of various parameters, such as fluence, number of pulses, laser beam polarization, wavelength, incident angle, scan velocity, number of scans, and environment, on the formation of different structures is discussed in detail wherever possible. Furthermore, a guideline for surface structures optimization is provided. The authors’ experimental work on laser-inscribed regular pattern fabrication is presented to give a complete picture of micromachining processes. Finally, possible applications of laser-machined surface structures in different fields are briefly reviewed.

Bottom-up synthesis of high surface area mesoporous crystalline silicon and evaluation of its hydrogen evolution performance

Abstract: Porous silicon is a technologically important material; however, many top-down etching fabrication processes result in significant material wastage. Here, the authors report a bottom-up self-templating fabrication route and assess the hydrogen evolution performance of the resulting material.

Activated Carbon-Coated Carbon Nanotubes for Energy Storage in Supercapacitors and Capacitive Water Purification

Abstract: Polypyrrole-coated multiwalled carbon nanotubes (PPy-MWCNT) were used for the fabrication of activated carbon-coated MWCNT doped with nitrogen (N-AC-MWCNT). The conceptually new method for the fabrication of non-agglomerated PPy-MWCNT with good coating uniformity allowed the fabrication of uniform and well-dispersed N-AC-MWCNT with high surface area. The use of N-AC-MWCNT allowed the fabrication of supercapacitor electrodes with high mass loading in the range of 15–35 mg cm–2 and with a high active material to current collector mass ratio of 0.21–0.50. The N-AC-MWCNT electrodes showed excellent electrochemical performance in aqueous 0.5 M Na2SO4 electrolyte. The maximum specific capacitance of 3.6 F cm–2 (103.1 F g–1) was achieved for mass loading of 35 mg cm–2 at a scan rate of 2 mV s–1. The aqueous supercapacitor cells, based on N-AC-MWCNT electrodes, exhibited excellent performance with energy density of 16.1 mWh g–1, power density of 14.4 W g–1, and enlarged voltage window of 1.8 V. The individual ele...

Photolithographic fabrication of high-performance all-solid-state graphene-based planar micro-supercapacitors with different interdigital fingers

Abstract: Here we demonstrated the fabrication of ultrahigh rate, all-solid-state, planar interdigital graphene-based micro-supercapacitors (MSCs) manufactured by methane plasma-assisted reduction and photolithographic micro-fabrication of graphene oxide films on silicon wafers. Notably, the electrochemical performance of MSCs is significantly enhanced by increasing the number of the interdigital fingers from 8 to 32 and minimizing the finger width from 1175 to 219 μm, highlighting the critical importance of adjusting the number and widths of the fingers in the fabrication of high-performance MSCs. The fabricated graphene-based MSCs delivered an area capacitance of 116 μF cm−2 and a stack capacitance of 25.9 F cm−3. Furthermore, they offered a power density of 1270 W cm−3 that is much higher than that of electrolytic capacitors, an energy density of ∼3.6 mW h cm−3 that is comparable to that of lithium thin-film batteries, and a superior cycling stability of ∼98.5% capacitance retention after 50000 cycles. More importantly, the microdevice can operate well at an ultrahigh scan rate of up to 2000 V s−1, which is three orders of magnitude higher than that of conventional supercapacitors.

Rapid annealing of reactively sputtered precursors for Cu2ZnSnS4 solar cells

Abstract: Cu2ZnSnS4 (CZTS) is a promising thin-film absorber material that presents some interesting challenges in fabrication when compared with Cu(In,Ga)Se2. We introduce a two-step process for fabrication ...

Room‐Temperature Printing of Organic Thin‐Film Transistors with π‐Junction Gold Nanoparticles

Abstract: Printing semiconductor devices under ambient atmospheric conditions is a promising method for the large-area, low-cost fabrication of flelectronic products. However, processes conducted at temperatures greater than 150 °C are typically used for printed electronics, which prevents the use of common fl exible substrates because of the distortion caused by heat. The present report describes a method for the room-temperature printing of electronics, which allows thin-fi lm electronic devices to be printed at room temperature without the application of heat. The development of π-junction gold nanoparticles as the electrode material permits the room-temperature deposition of a conductive metal layer. Room-temperature patterning methods are also developed for the Au ink electrodes and an active organic semiconductor layer, which enables the fabrication of organic thin-fi lm transistors through room-temperature printing. The transistor devices printed at room temperature exhibit average fi eld-effect mobilities of 7.9 and 2.5 cm 2 V −1 s −1 on plastic and paper substrates, respectively. These results suggest that this fabrication method is very promising as a core technology for low-cost and high-performance printed electronics.

Facile fabrication of a well-ordered porous Cu-doped SnO2 thin film for H2S sensing.

Abstract: Well-ordered Cu-doped and undoped SnO2 porous thin films with large specific surface areas have been fabricated on a desired substrate using a self-assembled soft template combined with simple physical cosputtering deposition. The Cu-doped SnO2 porous film gas sensor shows a significant enhancement in its sensing performance, including a high sensitivity, selectivity, and a fast response and recovery time. The sensitivity of the Cu-doped SnO2 porous sensor is 1 order of magnitude higher than that of the undoped SnO2 sensor, with average response and recovery times to 100 ppm of H2S of ∼10.1 and ∼42.4 s, respectively, at the optimal operating temperature of 180 °C. The well-defined porous sensors fabricated by the method also exhibit high reproducibility because of the accurately controlled fabrication process. The facile process can be easily extended to the fabrication of other semiconductor oxide gas sensors with easy doping and multilayer porous nanostructure for practical sensing applications.

Versatile Fabrication of Complex Shaped Metal Oxide Nano-Microstructures and Their Interconnected Networks for Multifunctional Applications

Abstract: Metal oxide nano-microstructures are applied in photocatalytic surfaces, sensors or biomedical engineering, proving the versatile utilization of nanotechnology. However, more complex or interconnected nano-microstructures are still seldomly met in practical applications, although they are of higher interest, due to enhanced structural, electronic and piezoelectric properties, as well as several complex biomedical effects, like antiviral characteristics. Here we attempt to present an overview of the novel, facile and cost-efficient flame transport synthesis (FTS) which allows controlled growth of different nano-microstructures and their interconnected networks in a scalable process. Various morphologies of nano-microstructures synthesized by FTS and its variants are demonstrated. These nano-microstructures have shown potential applications in different fields and the most relevant are reviewed here. Fabrication, growth mechanisms and properties of such large and highly porous three-dimensional (3D) interconnected networks of metal oxides (ZnO, SnO2, Fe2O3) nano-microstructures including carbon based aerographite material using FTS approaches are discussed along with their potential applications.

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

Abstract: The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.

Tensile Ge microstructures for lasing fabricated by means of a silicon complementary metal-oxide-semiconductor process

Abstract: In this work we study, using experiments and theoretical modeling, the mechanical and optical properties of tensile strained Ge microstructures directly fabricated in a state-of-the art complementary metal-oxide-semiconductor fabrication line, using fully qualified materials and methods. We show that these microstructures can be used as active lasing materials in mm-long Fabry-Perot cavities, taking advantage of strain-enhanced direct band gap recombination. The results of our study can be realistically applied to the fabrication of a prototype platform for monolithic integration of near infrared laser sources for silicon photonics.

RCE-DR, a novel process for coated conductor fabrication with high performance

Abstract: We report in detail on SuNAM's reactive co-evaporation by deposition and reaction (RCE-DR) process. We have successfully fabricated a high performance GdBCO coated conductor (CC) with high throughput by the RCE-DR process, that consists of two steps for the deposition of elemental metal oxides and the conversion of cation oxides into the GdBCO superconducting phase. Constituting metals such as Gd, Ba and Cu were first deposited on LaMnO3 (LMO)-buffered IBAD-MgO templates at low temperatures and low pressures followed by a high temperature treatment step under high oxygen partial pressure for fast phase conversion. GdBCO CCs fabricated by RCE-DR showed excellent transport properties such as a critical current of 794 A cm−1 width at 77 K in self-field. With the RCE-DR process, we have achieved an overall processing speed of more than 120 m h−1 (in terms of a real process linear tape speed equivalent). SuNAM's RCE-DR technique showed great potential as the highest throughput fabrication process compared with other methods developed previously for second generation high temperature superconducting wires, meeting the current and future need of industry in terms of price and production speed.

High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric

Abstract: One of the key advantages of organic field-effect transistors (OFETs) is their ability to form flexible, conformable and lightweight electronic devices, e.g. radio frequency identification (RFID) tags,[1] microprocessors[2] and flexible displays.[3] These require fabrication over large-areas on flexible plastic substrates, the poor dimensional stability of such substrates creating the additional demand of low-temperature processing (<200 °C).[4] While high performance source, drain and gate electrodes and interconnects require metal evaporation under vacuum, ideally the dielectric and organic semiconductor (OSC) should be processed from solution under ambient conditions to reduce fabrication costs. Regarding device architecture, OFETs with a bottom-gate (BG) bottom-contact (BC) geometry (Figure ​1c)1c) have an advantage in that the organic semiconducting layer is deposited last.[5] This affords easy fabrication and patterning of micron-scale OFET channels, electrodes and interconnects by conventional photolithographic methods, whilst avoiding exposure of the active OSC material to UV radiation and aggressive or solubilising chemicals. Furthermore, this architecture is compatible with vacuum sublimation or vapour phase techniques for OSC deposition, allowing access to a wide range of high-performance materials. Such OFETs can form the building blocks of high performance, low-cost electronic circuitry.

Sub-15-nm patterning of asymmetric metal electrodes and devices by adhesion lithography

Abstract: Coplanar electrodes formed from asymmetric metals separated on the nanometre length scale are essential elements of nanoscale photonic and electronic devices. Existing fabrication methods typically involve electron-beam lithography—a technique that enables high fidelity patterning but suffers from significant limitations in terms of low throughput, poor scalability to large areas and restrictive choice of substrate and electrode materials. Here, we describe a versatile method for the rapid fabrication of asymmetric nanogap electrodes that exploits the ability of selected self-assembled monolayers to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. The method may be carried out under ambient conditions using simple equipment and a minimum of processing steps, enabling the rapid fabrication of nanogap electrodes and optoelectronic devices with aspect ratios in excess of 100,000.

Multi-material metallic structure fabrication using electron beam melting

Abstract: The fabrication of multi-material structures using Ti–6Al–4V and copper was explored with the additive manufacturing (AM) technology of electron beam melting (EBM). A new method was developed that included multiple build sequences to accommodate both materials. The process was enabled by machining a start plate so that the parts built with the first material could be press fit into the plate, providing a flat surface on which the second material fabrication would occur. This method provided the ability to fabricate simple multiple metallic material components built in the Z and X directions [1]. Registration of the electron beam was performed manually resulting in slight misalignment for the shift of diameters of specimens built in the Z direction, and along the width and length for specimens built in the X direction. Microstructures observed and hardness values measured for copper and Ti–6Al–4V were different to those observed in normally fabricated EBM parts. These observations might be explained by the different processing conditions required for multi-material fabrication in contrast to the regular EBM process where parts are built in a single machine run. The hardness profiles for as-fabricated and HIPed multi-material parts depicted an increase in hardness for both materials close to the interface with values leveling off to those of single material EBM fabricated parts as measurements proceeded away from the interface. As the benefits of EBM processing are exploited, the method introduced in this research can have profound implications in many technological applications including metal extraction, energy production and for the repair of metallic components.

Template assisted fabrication of free-standing MnO2 nanotube and nanowire arrays and their application in supercapacitors

Abstract: In this Letter, an innovative technique is reported to control the fabrication of free-standing MnO2 nanotube and nanowire arrays. The synthesis is based on a three-step process, using porous anodic aluminum oxide as a template, and enables the selective fabrication of vertically aligned MnO2 nanotubes or nanowires on large areas. The as-prepared MnO2 nanotube and nanowire arrays are investigated as electrode materials for supercapacitor applications and show a good electrochemical performance with specific capacitances of 210 F g−1 at 1.9 A g−1 and 231 F g−1 at 0.5 A g−1, respectively. The investigation of the rate capability of both structures indicates a superior performance of the nanotube arrays.

Fabrication of three-dimensional microfluidic channels in a single layer of cellulose paper

Abstract: Three-dimensional microfluidic paper-based analytical devices (3D-μPADs) represent a promising platform technology that permits complex fluid manipulation, parallel sample distribution, high throughput, and multiplexed analytical tests. Conventional fabrication techniques of 3D-μPADs always involve stacking and assembling layers of patterned paper using adhesives, which are tedious and time-consuming. This paper reports a novel technique for fabricating 3D microfluidic channels in a single layer of cellulose paper, which greatly simplifies the fabrication process of 3D-μPADs. This technique, evolved from the popular wax-printing technique for paper channel patterning, is capable of controlling the penetration depth of melted wax, printed on both sides of a paper substrate, and thus forming multilayers of patterned channels in the substrate. We control two fabrication parameters, the density of printed wax (i.e., grayscale level of printing) and the heating time, to adjust the penetration depth of wax upon heating. Through double-sided printing of patterns at different grayscale levels and proper selection of the heating time, we construct up to four layers of channels in a 315.4-μm-thick sheet of paper. As a proof-of-concept demonstration, we fabricate a 3D-μPAD with three layers of channels from a paper substrate and demonstrate multiplexed enzymatic detection of three biomarkers (glucose, lactate, and uric acid). This technique is also compatible with the conventional fabrication techniques of 3D-μPADs, and can decrease the number of paper layers required for forming a 3D-μPAD and therefore make the device quality control easier. This technique holds a great potential to further popularize the use of 3D-μPADs and enhance the mass-production quality of these devices.

Top-down fabrication of three-dimensional porous V2O5 hierarchical microplates with tunable porosity for improved lithium battery performance

Abstract: Three-dimensional porous V2O5 hierarchical microplates have been fabricated by a one-step top-down strategy, and display an excellent rate capability and stable capacity of 110 mA h g−1 at 2000 mA g−1 after 100 cycles. We have demonstrated that the facile approach of a solid-phase conversion is promising for large-scale fabrication of highly porous micro/nano materials.

Challenges in the fabrication of fibre Bragg gratings in silica and polymer microstructured optical fibres

Abstract: This paper reviews the state-of-the-art of grating fabrication in silica and polymer microstructured optical fibres. It focuses on the difficulties and challenges encountered during photo-inscription of such gratings and more specifically on the effect of the air hole lattice microstructure in the cladding of the fibre on the transverse coupling of the coherent writing light to the core region of the fibre. Experimental and computational quantities introduced thus far to assess the influence of the photonic crystal lattice on grating writing efficiency are reviewed as well, together with techniques that have been proposed to mitigate this influence. Finally, early proposals to adapt the microstructure in view of possibly enhancing multi-photon grating fabrication efficiency are discussed.

Fabrication tolerant and broadband polarization splitter and rotator based on a taper-etched directional coupler.

Abstract: We propose a fabrication tolerant polarization splitter and rotator (PSR) on the silicon-on-insulator platform based on the mode-coupling mechanism. The PSR consists of a silicon wire waveguide coupled to a taper-etched waveguide. Compared to previously reported PSRs based on directional couplers which are sensitive to fabrication variations, the partially etched taper structure can compensate for fabrication inaccuracies. In addition, the taper-etched geometry breaks both the horizontal and vertical symmetries of the waveguide, introducing an additional degree of design freedom to accommodate different upper cladding layers. The proposed PSR can be readily integrated in a planar waveguide circuit using e.g. SiO2 cladding, making it compatible with typical metal back-end-of-line processes. Our simulation results show that the PSR has a low TM-to-TE polarization conversion loss of −0.09 dB in the C-band (or a conversion efficiency of 98%). A low TE-to-TE through insertion loss (−0.07 dB) and a very low polarization crosstalk (−30 dB) over a wide wavelength range exceeding 160 nm with a large fabrication tolerance (>50 nm) are numerically demonstrated.

Flexible, in-plane, and all-solid-state micro-supercapacitors based on printed interdigital Au/polyaniline network hybrid electrodes on a chip

Abstract: A simple and rapid fabrication method involving laser printing technology and in situ anodic electropolymerization is introduced to fabricate interdigital Au/polyaniline network hybrid electrodes on polyethylene terephthalate films for flexible, in-plane, and all-solid-state micro-supercapacitors. The as-obtained micro-supercapacitors acquire a maximum energy density of 5.83 mW h cm−3 and a maximum power density of 0.45 W cm−3 that are both comparable to or superior to the values obtained for currently available state-of-the-art planar supercapacitors/micro-supercapacitors. In addition, the micro-supercapacitors exhibit remarkably high mechanical flexibility and show a good cycling stability, with 72.7% retention of the specific capacity after 1000 cycles. Moreover, the micro-supercapacitors can be optionally connected in series or in parallel to meet the voltage and capacity requirements for a given application. Compared to traditional fabrication approaches for flexible micro-supercapacitors with an interdigital in-plane design, the method demonstrated here does not involve a complicated lithography process, toxic chemical treatments, expensive rigid template, and cumbersome fabrication of jettable and stable precursor ink, which provides a simple route for fabrication of flexible planar micro-supercapacitors with high-practicality and high-performance.

High conductivity micro-wires in diamond following arbitrary paths

Abstract: High quality graphitic wires embedded beneath the surface of single crystal diamond are fabricated using a combination of adaptive ultrashort pulsed laser fabrication, high numerical aperture focusing, and an axial multi-fabrication scheme. Wires are created with micrometer and sub-micrometer dimensions that can follow any three dimensional path within the diamond. The measured conductivities are over an order of magnitude greater than previously reported wires fabricated by ultra-short pulsed lasers. The increased level of graphitization control in this scheme appears particularly important for fabrication of wires parallel to the diamond surface.

Fabricating Copper Components with Electron Beam Melting

Abstract: ADVANCED MATERIALS & PROCESSES • JULY 2014 20 Direct fabrication of fully dense metal structures using the electron beam melting (EBM) process developed by Arcam AB, Sweden, has been successfully demonstrated for a wide range of materials including Ti-6Al-4V[1,11,9], cobalt chromium[7,6], titanium-aluminide[4,8], H-13 steel[2], and nickelbase alloys[10]. A growing interest in additive manufacturing (AM) to build components from copper and copper alloys[5,13,12] is spurring a variety of applications including novel radio frequency (RF) accelerating structures. A critical issue for high average power, high brightness photoinjectors—the technology of choice for generating high brightness electron beams used in many of today’s linear accelerators—is efficient cooling. RadiaBeam Technologies is exploring the use of AM to fabricate complex RF photoinjectors with geometries optimized for thermal management: Spatially optimized internal cooling channels can be fabricated without the constraints typically associated with traditional manufacturing methods. However, several properties of pure copper present significant processing challenges for direct metal AM. For one, pure copper has a relatively high thermal conductivity (401 W•m−1•K−1 at 300K) which, while ideal for thermal management applications, rapidly conducts heat away from the melt area resulting in local thermal gradients. This can lead to layer curling, delamination, and ultimately, build and part failure. Additionally, copper’s high ductility hinders post-build powder removal and recovery. Particles also tend to agglomerate, reducing overall flowability and impeding powder deposition. Because Cu is sensitive to oxidation, great care must be taken in handling and storage before, during, and after part fabrication.

Fabrication of textile based conductometric polyaniline gas sensor

Abstract: In this work, we report the fabrication of gas sensors prepared by in situ polymerization of aniline on non-woven fabrics. It is anticipated that a thin coating of polyaniline film fabricated on porous fabric material would improve the performance of the polyaniline based gas sensor. The hypothesis is based on the recent improved technique that allows the fabrication of nanoparticle based polyaniline film, and the high gas permeability of the fabrics. Sensor fabrication parameters which included acidity of reaction media, precursor and reagent concentrations, and the number of modification cycle have been studied. The resulting gas sensors were found to be highly responsive to a range of volatile organic compounds (VOCs). This high sensitivity was also accompanied with fast response time (∼10 s). The order of sensitivity to VOCs was found to be ethanol > chloroform > toluene > acetone > ethyl acetate. Further, the sensor was three orders of magnitude more sensitive to ammonia than all organic vapours tested.

Fabrication and heat treatment of ceramic-reinforced aluminium matrix composites - a review

Abstract: Ceramic-reinforced aluminium matrix composites have attracted considerable attention in engineering applications as a result of their relatively low costs and characteristic isotropic properties. Reinforcement materials include carbides, nitrides and oxides. In an effort to achieve optimality in structure and properties of ceramic-reinforced metal matrix composites (MMCs), various fabrication and heat treatment techniques have evolved over the last 20 years. In this paper, the status of the research and development in fabrication and heat treatment techniques of ceramic-reinforced aluminium matrix composites is reviewed, with a major focus on material systems in terms of chemical compositions, weight or volume fraction, particle size of reinforcement, fabrication methods and heat treatment procedures. Various optical measurement techniques used by the researchers are highlighted. Also, limitations and needs of the technique in composite fabrication are presented in the literature. The full potential of various methods for fabricating ceramic-reinforced aluminium matrix composites is yet to be explored.