Showing papers on "Fabrication published in 2012"

Fabrication of Single‐ and Multilayer MoS2 Film‐Based Field‐Effect Transistors for Sensing NO at Room Temperature

Abstract: Single- and multilayer MoS(2) films are deposited onto Si/SiO(2) using the mechanical exfoliation technique. The films were then used for the fabrication of field-effect transistors (FETs). These FET devices can be used as gas sensors to detect nitrous oxide (NO). Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable. The two-, three-, and four-layer MoS(2) devices show both stable and sensitive responses to NO down to a concentration of 0.8 ppm.

Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors

Abstract: carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Fabrication of flexible MoS2 thin-film transistor arrays for practical gas-sensing applications.

Abstract: By combining two kinds of solution-processable two-dimensional materials, a flexible transistor array is fabricated in which MoS2 thin film is used as the active channel and reduced graphene oxide (rGO) film is used as the drain and source electrodes. The simple device configuration and the 1.5 mm-long MoS2 channel ensure highly reproducible device fabrication and operation. This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility. Compared to using rGO thin film as the active channel, this new gas sensor exhibits much higher sensitivity. Moreover, functionalization of the MoS2 thin film with Pt nanoparticles further increases the sensitivity by up to ∼3 times. The successful incorporation of a MoS2 thin-film into the electronic sensor promises its potential application in various electronic devices.

Integrating stereolithography and direct print technologies for 3D structural electronics fabrication

Abstract: Purpose – The purpose of this paper is to present a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three‐dimensional (3D) structures with embedded electronic circuits. A detailed process was developed that enables fabrication of monolithic 3D packages with electronics without removal from the hybrid SL/DP machine during the process. Successful devices are demonstrated consisting of simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).Design/methodology/approach – A hybrid SL/DP system was designed and developed using a 3D Systems SL 250/50 machine and an nScrypt micro‐dispensing pump integrated within the SL machine through orthogonally‐aligned linear translation stages. A corresponding manufacturing process was also developed using this system to fabricate 2D and 3D monolithic structures with embedded electronic circuits. The process involved part de...

Synthesis of Ultralong Copper Nanowires for High-Performance Transparent Electrodes

Abstract: Cu nanowires hold great promise for the fabrication of low-cost transparent electrodes. However, their current synthesis is mainly performed in aqueous media with poor nanowire dispersibility. We report herein the novel synthesis of ultralong single-crystalline Cu nanowires with excellent dispersibility, providing an excellent candidate material for high-performance transparent electrode fabrication.

Large Area Fabrication of Leaning Silicon Nanopillars for Surface Enhanced Raman Spectroscopy

Abstract: Using a simple two step fabrication process substrates with a large and uniform Raman enhancement, based on flexible free standing nanopillars can be manufactured over large areas using readily available silicon processing equipment.

Rod‐Coating: Towards Large‐Area Fabrication of Uniform Reduced Graphene Oxide Films for Flexible Touch Screens

Abstract: A novel strategy is developed for the large-scale fabrication of reduced graphene oxide films directly on flexible substrates in a controlled manner by the combination of a rod-coating technique and room-temperature reduction of graphene oxide. The as-prepared films display excellent uniformity, good transparency and conductivity, and great flexibility in a touch screen.

Free-standing mechanical and photonic nanostructures in single-crystal diamond.

Abstract: A variety of nanoscale photonic, mechanical, electronic, and optoelectronic devices require scalable thin film fabrication. Typically, the device layer is defined by thin film deposition on a substrate of a different material, and optical or electrical isolation is provided by the material properties of the substrate or by removal of the substrate. For a number of materials this planar approach is not feasible, and new fabrication techniques are required to realize complex nanoscale devices. Here, we report a three-dimensional fabrication technique based on anisotropic plasma etching at an oblique angle to the sample surface. As a proof of concept, this angled-etching methodology is used to fabricate free-standing nanoscale components in bulk single-crystal diamond, including nanobeam mechanical resonators, optical waveguides, and photonic crystal and microdisk cavities. Potential applications of the fabricated prototypes range from classical and quantum photonic devices to nanomechanical-based sensors and actuators.

Magnetic Nanoparticles : From Fabrication to Clinical Applications

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Reducing extrinsic performance-limiting factors in graphene grown by chemical vapor deposition.

Abstract: Field-effect transistors fabricated on graphene grown by chemical vapor deposition (CVD) often exhibit large hysteresis accompanied by low mobility, high positive backgate voltage corresponding to the minimum conductivity point (Vmin), and high intrinsic carrier concentration (n0). In this report, we show that the mobility reported to date for CVD graphene devices on SiO2 is limited by trapped water between the graphene and SiO2 substrate, impurities introduced during the transfer process and adsorbates acquired from the ambient. We systematically study the origin of the scattering impurities and report on a process which achieves the highest mobility (μ) reported to date on large-area devices for CVD graphene on SiO2: maximum mobility (μmax) of 7800 cm2/(V·s) measured at room temperature and 12 700 cm2/(V·s) at 77 K. These mobility values are close to those reported for exfoliated graphene on SiO2 and can be obtained through the careful control of device fabrication steps including minimizing resist resi...

94 GHz Substrate Integrated Monopulse Antenna Array

Abstract: A planar W-band monopulse antenna array is designed based on the substrate integrated waveguide (SIW) technology The sum-difference comparator, 16-way divider and 32 × 32 slot array antenna are all integrated on a single dielectric substrate in the compact layout through the low-cost PCB process Such a substrate integrated monopulse array is able to operate over 93 ~ 96 GHz with narrow-beam and high-gain The maximal gain is measured to be 258 dBi, while the maximal null-depth is measured to be - 437 dB This SIW monopulse antenna not only has advantages of low-cost, light, easy-fabrication, etc, but also has good performance validated by measurements It presents an excellent candidate for W-band directional-finding systems

Narrow-band waveguide Bragg gratings on SOI wafers with CMOS-compatible fabrication process.

Abstract: We demonstrate the design, fabrication and measurement of integrated Bragg gratings in a compact single-mode silicon-on-insulator ridge waveguide. The gratings are realized by corrugating the sidewalls of the waveguide, either on the ridge or on the slab. The coupling coefficient is varied by changing the corrugation width which allows precise control of the bandwidth and has a high fabrication tolerance. The grating devices are fabricated using a CMOS-compatible process with 193 nm deep ultraviolet lithography. Spectral measurements show bandwidths as narrow as 0.4 nm, which are promising for on-chip applications that require narrow bandwidths such as WDM channel filters. We also present the die-to-die nonuniformity for the grating devices on the wafer, and our analysis shows that the Bragg wavelength deviation is mainly caused by the wafer thickness variation.

High-Efficiency Solid-State Dye-Sensitized Solar Cells Based on TiO2-Coated ZnO Nanowire Arrays

Abstract: Replacing the liquid electrolytes in dye-sensitized solar cells (DSCs) with solid-state hole-transporting materials (HTMs) may solve the packaging challenge and improve the long-term stability of DSCs. The efficiencies of such solid-state DSCs (ss-DSCs), however, have been far below the efficiencies of their counterparts that use liquid electrolytes, primarily due to the challenges in filling HTMs into thick enough sensitized films based on sintered TiO2 nanoparticles. Here we report fabrication of high-efficiency ss-DSCs using multilayer TiO2-coated ZnO nanowire arrays as the photoanodes. The straight channel between the vertically aligned nanostructures combined with a newly developed multistep HTM filling process allows us to effectively fill sensitized films as thick as 50 μm with the HTMs. The resulting ss-DSCs yield an average power conversion efficiency of 5.65%.

Reversibly Shape‐Shifting Organic Optical Waveguides: Formation of Organic Nanorings, Nanotubes, and Nanosheets

Abstract: because the functions of thenanoobjects are dependent on their shape and dimensions. Inthe area of organic nanophotonics in particular, the confine-ment of optical waves in shape-shifting organic nanostruc-tures is interesting because of their potential use in “smart”nanooptical devices, such as optical waveguides, photonicdetectors, and optical sensors.Until now, no methods for the fabrication of reversiblyshape-shifting organic nanostructures that have dimension-ally dependent optical waveguiding properties have beenavailable. Most of the reported organic waveguides havedefined shapes

Valuing Reversible Energy Storage

Abstract: The development of new materials that provide the capability of high-performance energy storage combined with flexibility of fabrication opens up the possibility of a wide range of technological applications. On page 1326 of this issue, El-Kady et al. ( 1 ) describe thin and highly flexible electrochemical capacitors (ECs) that were created by means of a very simple and innovative process. Unlike the usual approaches of making thin graphene electrodes that start with a particulate and use roll-coating, screen printing, or ink-jet printing ( 2 ), their process involves focusing a low-power laser onto a thin graphene oxide deposit to convert it into graphene. The incorporation of graphene in electrodes created with mechanical processes tends to be in agglomerates that provide little performance advantage over traditional particulate-activated carbon electrodes. El-Kady et al. 's approach also contrasts with plasma-assisted chemical vapor deposition processes that have been used to grow vertically oriented graphene nanosheet electrodes ( 3 ). Although graphene structures grown by such methods are well-formed and offer performance advantages over traditional activated carbon materials, they require complicated vacuum process equipment, plus the graphene growth rate is very slow ( 4 ). The somewhat simple EC electrode fabrication process reported by El-Kady et al. therefore appears to circumvent many of the difficulties encountered with traditional processes.

Graphene-ferroelectric hybrid structure for flexible transparent electrodes.

Abstract: Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 × 1013 cm–2 by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Ω/□ at ambient conditions. The graphene–ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new ro...

Oxide thin film transistor and method of fabricating the same

Abstract: An oxide thin film transistor (TFT) and a fabrication method thereof are provided. First and second data wirings are made of different metal materials, and an active layer is formed on the first data wiring to implement a short channel, thus enhancing performance of the TFT. The first data wiring in contact with the active layer is made of a metal material having excellent contact characteristics and the other remaining second data wiring is made of a metal material having excellent conductivity, so as to be utilized to a large-scale oxide TFT process. Also, the first and second data wirings may be formed together by using half-tone exposure, simplifying the process.

Laser micro-fabrication of concave, low-roughness features in silica

Abstract: We describe a micro-fabrication method to create concave features with ultra-low roughness in silica, either on optical fibers or on flat substrates. The machining uses a single CO2 laser pulse train. Parameters are chosen such that evaporation removes material while a low-viscosity melt layer produces excellent surface quality. A surface roughness σ ∼ 0.2 nm is regularly obtained. The concave depressions are near-spherical close to the center with radii of curvature between 20 and 2000 μm. The method allows fabrication of low-scatter micro-optical devices such as mirror substrates for high-finesse cavities or negative lenses on fiber tips, extending the range of micro-optical components.

Step-by-step fabrication of a highly oriented crystalline three-dimensional pillared-layer-type metal-organic framework thin film confirmed by synchrotron X-ray diffraction.

Abstract: Fabrication of a crystalline ordered thin film based on the porous metal–organic frameworks (MOFs) is one of the practical applications of the future functional nanomaterials. Here, we report the creation of a highly oriented three-dimensional (3-D) porous pillared-layer-type MOF thin film on a metal substrate using a step-by-step approach based on liquid-phase epitaxy. Synchrotron X-ray diffraction (XRD) study clearly indicates that the thin film is crystalline and its orientation is highly controlled in both horizontal and vertical directions relative to the substrate. This report provides the first confirmation of details of not only the crystallinity but also the orientation of 3-D MOF thin film using synchrotron XRD. Moreover, we also demonstrate its guest adsorption/desorption behavior by using in situ XRD measurements. The results presented here would promise useful insights for fabrication of MOF-based nanodevices in the future.

Correlation between MgAl2O4-spinel structure, processing factors and functional properties of transparent parts (progress review)

Abstract: Efforts were and are made to develop performant fabrication technologies, for transparent polycrystalline spinel – a material used for armor, infrared windows and other products. Significant progress was made – during some fifty years of research – regarding the understanding of the structure of spinel, at various scales, and the best ways to correlate processing with the relevant structural features so as to improve properties. This review compiles and comments the results of this progress, using as sources the literature and the author's own work. As of now the best specimens obtained combine submicron grains with an optical transmission close to the theoretical and a Vickers hardness of 15 GPa (size ≤25 cm). Larger plates, more than 0.5 m in size, but with coarse microstructure and lower hardness, have also been produced, together with quite large dome shaped parts, exhibiting highly uniform optical properties.

In situ synthesizing Al3Ni for fabrication of intermetallic-reinforced aluminum alloy composites by friction stir processing

Abstract: Ultrafine-grained in situ synthesized Al3Ni particulate-reinforced composites were fabricated by friction stir processing (FSP) introduced Ni powder into the stirred zone of 1100-H14 aluminum alloy. The microstructures and the compositions of the composites were analyzed by SEM, EDS and XRD. The microhardness and ultimate tensile strength (UTS) were measured. The XRD and EDS analyses showed that the Al–Ni in situ synthesizing product was Al3Ni. When the specimen was stirred 2 passes, the formed Al3Ni was tiny to be detected. Al3Ni subsequently became apparent when stirring 4 and 6 passes and the fine Al3Ni particles were dispersed homogeneously in the composites, which caused significant increases of the microhardness and UTS of the composites. The effective Gibbs free energy change of formation model was proposed to predict the Al–Ni compound formation at solid-state interface and the calculation combined with kinetic factors showed that Al3Ni was the product, which supports the experimental observation.

High-Q MEMS Resonators for Laser Beam Scanning Displays

Abstract: This paper reports on design, fabrication and characterization of high-Q MEMS resonators to be used in optical applications like laser displays and LIDAR range sensors. Stacked vertical comb drives for electrostatic actuation of single-axis scanners and biaxial MEMS mirrors were realized in a dual layer polysilicon SOI process. High Q-factors up to 145,000 have been achieved applying wafer level vacuum packaging technology including deposition of titanium thin film getters. The effective reduction of gas damping allows the MEMS actuator to achieve large amplitudes at high oscillation frequencies while driving voltage and power consumption can be minimized. Exemplarily shown is a micro scanner that achieves a total optical scan angle of 86 degrees at a resonant frequency of 30.8 kHz, which fulfills the requirements for HD720 resolution. Furthermore, results of a new wafer based glass-forming technology for fabrication of three dimensionally shaped glass lids with tilted optical windows are presented.

Reduced graphene Oxide–MnO2 hollow sphere hybrid nanostructures as high-performance electrochemical capacitors

Abstract: This paper presents the first successful fabrication of reduced graphene oxide (RGO)–MnO2 hollow sphere (HS) hybrid electrode materials through a solution-based ultrasonic co-assembly method. The porous structure of these MnO2 hollow spheres and the excellent dispersion of active materials give the as-fabricated RGO–MnO2 HS hybrid electrodes excellent specific capacitance and energy density, which can reach up to 578 F g−1 and 69.8 W h kg−1, respectively. These values are considerably larger than those of most reported graphene–MnO2 based hybrid electrochemical capacitors. This solution-processed method can also be used for the hybridization of graphene with other metal oxides in the fabrication of high-performance electrochemical capacitors.

Ferromagnetic Josephson switching device with high characteristic voltage

Abstract: We develop a fast Magnetic Josephson Junction (MJJ) - a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient Single Flux Quantum (SFQ) circuits. We present experimental results for Superconductor-Insulator-Ferromagnet-Superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 uV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ~30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.

Fabrication of hollow core carbon spheres with hierarchical nanoarchitecture for ultrahigh electrical charge storage

Abstract: A simple and reproducible sol–gel synthesis strategy was developed to fabricate hollow core carbon spheres (HCCSs) with hierarchical nanoarchitecture through the hydrolysis, self-assembly and co-condensation of bis-[3-(triethoxysilyl)propyl]disulfide (TESPDS) and octadecyltrimethoxysilane (C18TMS). This synthesis route allows one to fabricate thioether-bridged organosilica (TBOS) with tailored spherical structure and particle size which can be further converted to HCCS upon calcination under N2 flow. It is assumed that hydrophobic octadecyl chains of hydrolyzed C18TMS first form a micelle-like self-assembly structure with hydrophilic trihydroxysilyl groups as heads, and a reactive core is then expanded by the base-catalyzed co-condensation of TESPDS and/or C18TMS over the C18TMS self-assembly structure. The organic moieties of TESPDS and C18TMS not only serve as a porogen during the formation of TBOS but also as a carbon precursor for transformation of TBOS into HCCS during the carbonization. Due to its unique hierarchical nanostructure composed of hollow macroporous core and meso/microporous shell, which facilitates fast mass transport, along with large surface area for electrical charge storage, the HCCS for the first time exhibits ultrahigh specific capacitance and energy, good cycling performance and rate capability.

Semiconductor die assemblies, semiconductor devices including same, and methods of fabrication

Abstract: Methods of fabricating multi-die assemblies including a wafer segment having no integrated circuitry thereon and having a plurality of vertically stacked dice thereon electrically interconnected by conductive through vias, resulting multi-die assemblies, and semiconductor devices comprising such multi-die assemblies. The wafer segment may function as a heat sink to enhance heat transfer from the stacked dice in the resulting multi-die assembly. The die stacks are fabricated at the wafer level on a base wafer, from which the wafer segment and die stacks are singulated after at least peripheral encapsulation.

Magnetic field alignment of block copolymers and polymer nanocomposites: Scalable microstructure control in functional soft materials

Abstract: Block copolymers (BCPs) offer an exciting range of structures and functions that are of potential utility in existing as well as emerging technologies. Although this is generally acknowledged, with few exceptions, viable strategies for establishing scalable and robust control of BCP microstructure are underdeveloped. Magnetic field alignment offers great potential in this regard. The physics bears much in common with electric field alignment, but the absence of dielectric breakdown concerns and the more flexible, space pervasive nature of magnetic fields make it possible to design processes for high-throughput fabrication of well-ordered films with appropriate materials. In this perspective, we highlight the use of magnetic fields for control of microstructure in BCPs as well as polymer nanocomposites involving anisotropic nanomaterials. A brief review of efforts to date is given. Open questions related to field-polymer interactions and future directions for magnetic alignment of these systems are discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011