Showing papers on "Fabrication published in 2010"

Direct Low-Temperature Nanographene CVD Synthesis over a Dielectric

Abstract: Graphenerankshighlyasapossiblematerialforfuturehigh-speedandflexibleelectronics.Current fabrication routes, which rely on metal substrates, require post-synthesis transfer of the graphene onto a Si wafer, or in the case of epitaxial growth on SiC, temperatures above 1000 °C are required. Both the handling difficultyandhightemperaturesarenotbestsuitedtopresentdaysilicontechnology.Wereportafacilechemical vapor deposition approach in which nanographene and few-layer nanographene are directly formed over magnesium oxide and can be achieved at temperatures as low as 325 °C.

An Asymmetrically Surface-Modified Graphene Film Electrochemical Actuator

Abstract: It is critically important to develop actuator systems for diverse needs ranging from robots and sensors to memory chips. The advancement of mechanical actuators depends on the development of new materials and rational structure design. In this study, we have developed a novel graphene electrochemical actuator based on a rationally designed monolithic graphene film with asymmetrically modified surfaces. Hexane and O2 plasma treatment were applied to the opposite sides of graphene film to induce the asymmetrical surface properties and hence asymmetrical electrochemical responses, responsible for actuation behaviors. The newly designed graphene actuator demonstrated here opens a new way for actuator fabrication and shows the potential of graphene film for applications in various electromechanical systems.

Droplet microfluidics for fabrication of non-spherical particles.

Abstract: We describe new developments for controlled fabrication of monodisperse non-spherical particles using droplet microfluidics. The high degree of control afforded by microfluidic technologies enables generation of single and multiple emulsion droplets. We show that these droplets can be transformed to non-spherical particles through further simple, spontaneous processing steps, including arrested coalescence, asymmetric polymer solidification, polymerization in microfluidic flow, and evaporation-driven clustering. These versatile and scalable microfluidic approaches can be used for producing large quantities of non-spherical particles that are monodisperse in both size and shape; these have great potential for commercial applications.

Metal microneedle fabrication using twisted light with spin

Abstract: Microneedle fabrication on a metal surface based on laser ablation using twisted light with spin was demonstrated, for the first time. The resulting needle showed a height of at least 10 μm above the target surface and a tip diameter of less than 0.3 μm. We also demonstrated the fabrication of a two-dimensional 5 × 6 microneedle array. The needles were uniformly well shaped with an average length and tip diameter of about 10 and 0.5 μm, respectively.

Interactive fabrication: new interfaces for digital fabrication

Abstract: We present a series of prototype devices that use real-time input to fabricate physical form: Interactive Fabrication. Our work maps out the problem space of real-time control for digital fabrication devices, and examines where alternative interfaces for digital fabrication are relevant. We conclude by reflecting upon the potential of interactive fabrication and outline a number of considerations for future research in this area.

Solution-Processed Inorganic Solar Cell Based on in Situ Synthesis and Film Deposition of CuInS2 Nanocrystals

Abstract: A novel, reproducible, and simple solution-based process for the fabrication of CuInS2 absorber layers and CdS buffer layers for photovoltaics is presented. In this process, a precursor solution is deposited on a substrate, after which sintered NCs are formed in situ at temperatures as low as 250 °C. Solar cell efficiencies of up to 4% have been demonstrated using this novel fabrication method.

Hybrid strategies in nanolithography

Abstract: Hybrid nanoscale patterning strategies combine the registration and addressability of conventional lithographic techniques with the chemical and physical functionality enabled by intermolecular, electrostatic and/or biological interactions. This review aims to highlight and to provide a comprehensive description of recent developments in hybrid nanoscale patterning strategies that enhance existing lithographic techniques or can be used to fabricate functional chemical patterns that interact with their environment. These functional structures create new capabilities, such as the fabrication of physicochemical surfaces that can recognize and capture analytes from complex liquid or gaseous mixtures. The nanolithographic techniques we describe can be classified into three general areas: traditional lithography, soft lithography and scanning-probe lithography. The strengths and limitations of each hybrid patterning technique will be discussed, along with the current and potential applications of the resulting patterned, functional surfaces.

Plasma-Assisted Approaches in Inorganic Nanostructure Fabrication

Abstract: Plasma is a unique medium for chemical reactions and materials preparations, which also finds its application in the current tide of nanostructure fabrication. Although plasma-assisted approaches have been long used in thin-film deposition and the top-down scheme of micro-/nanofabrication, fabrication of zero- and one-dimensional inorganic nanostructures through the bottom-up scheme is a relatively new focus of plasma application. In this article, recent plasma-assisted techniques in inorganic zero- and one-dimensional nanostructure fabrication are reviewed, which includes four categories of plasma-assisted approaches: plasma-enhanced chemical vapor deposition, thermal plasma sintering with liquid/solid feeding, thermal plasma evaporation and condensation, and plasma treatment of solids. The special effects and the advantages of plasmas on nanostructure fabrication are illustrated with examples, emphasizing on the understandings and ideas for controlling the growth, structure, and properties during plasma-assisted fabrications. This Review provides insight into the utilization of the special properties of plasmas in nanostructure fabrication.

Fabrication of microdevices with integrated nanowires for investigating low-dimensional phonon transport.

Abstract: Phonons in low-dimensional structures with feature sizes on the order of the phonon wavelength may be coherently scattered by the boundary. This may give rise to a new regime of heat conduction, which can impact thermal energy transport and conversion. Traditional methods used to investigate phonon transport in one-dimensional structures suffer from uncertainty due to contact resistance, defects, and limited control over sample dimensions. We have developed a new batch-fabrication technique for suspended microdevices with integrated silicon nanowires from silicon-on-insulator (SOI) wafers. The nanowires are defect-free and have extremely high aspect ratios (length/critical dimension >2000). The nanowire dimensions (length and critical dimension) can be precisely controlled during fabrication. With these novel devices, phonon transport in silicon nanowires is systematically investigated. The room temperature thermal conductivity of nanowires with critical width around 80 nm is about 20 W/(m K) and much lower than that in smooth VLS wires. This suggests that the surface morphology of the structures has a significant effect on the thermal conductivity, but this phenomenon is not currently understood. This fabrication technique can also be used for thermal transport investigation in a wide-range of low-dimensional structures.

Fabricating nanowire devices on diverse substrates by simple transfer-printing methods

Abstract: The fabrication of nanowire (NW) devices on diverse substrates is necessary for applications such as flexible electronics, conformable sensors, and transparent solar cells. Although NWs have been fabricated on plastic and glass by lithographic methods, the choice of device substrates is severely limited by the lithographic process temperature and substrate properties. Here we report three new transfer-printing methods for fabricating NW devices on diverse substrates including polydimethylsiloxane, Petri dishes, Kapton tapes, thermal release tapes, and many types of adhesive tapes. These transfer-printing methods rely on the differences in adhesion to transfer NWs, metal films, and devices from weakly adhesive donor substrates to more strongly adhesive receiver substrates. Electrical characterization of fabricated NW devices shows that reliable ohmic contacts are formed between NWs and electrodes. Moreover, we demonstrated that Si NW devices fabricated by the transfer-printing methods are robust piezoresistive stress sensors and temperature sensors with reliable performance.

Fabrication and Microstructure Control of Nanoscale Mechanical Testing Specimens via Electron Beam Lithography and Electroplating

Abstract: It has been demonstrated that the mechanical properties of materials change significantly when external dimensions are confined to the nanoscale. Currently, the dominant fabrication method for mechanical testing specimens with nanometer dimensions is by using focused ion beam (FIB) milling, which results in inevitable Ga+ induced damage to the microstructure. Here, we report a FIB-less fabrication technique to create arrays of vertically oriented gold and copper nanopillars based on patterning polymethylmethacrylate by electron beam lithography and subsequent electroplating into the prescribed template. This fabrication process is capable of producing a wide range of microstructures: from single crystals and nanotwinned, to bi-, poly-, and nanocrystalline mechanical testing specimens with diameters from 750 down to 25 nm with the diameter range below 100 nm previously inaccessible by FIB.

High-speed multiphoton absorption polymerization: fabrication of microfluidic channels with arbitrary cross-sections and high aspect ratios

Abstract: We demonstrate the use of high-speed, multiphoton absorption polymerization (MAP) for the fabrication of large-area microfluidic master structures. High-speed fabrication in SU8 without laser-induced damage is made possible by the use of a novel photoacid generator with a high two-photon-absorption cross-section. Master structures fabricated with MAP can be used to produce polydimethylsiloxane microchannels with high aspect ratios and/or arbitrary cross-sections. Microchannels with different cross-sections and heights can be combined readily in a single device. This fabrication technique significantly increases the diversity of channel architectures available for microfluidic devices.

High yield fabrication of chemically reduced graphene oxide field effect transistors by dielectrophoresis

Abstract: We demonstrate high yield fabrication of field effect transistors (FET) using chemically reduced graphene oxide (RGO) sheets suspended in water assembled via dielectrophoresis. The two terminal resistances of the devices were improved by an order of magnitude upon mild annealing at 200 0C in Ar/H2 environment for 1 hour. With the application of a backgate voltage, all of the devices showed FET behavior with maximum hole and electron mobilities of 4.0 and 1.5 cm2/Vs respectively. This study shows promise for scaled up fabrication of graphene based nanoelectronic devices.

PbS nanocrystal solar cells with high efficiency and fill factor

Abstract: We report on the fabrication of efficient PbS solar cells, showing power conversion efficiencies approaching 4% and fill factors of 60% under AM1.5 illumination. The effect of the size of two different nanocrystals (NCs) on the performance and key parameters of the devices are discussed together with peculiar features of device functioning. The results prove that the devices are not under space-charge limitation and the device performance is influenced by charge trapping which is dependent on the size of the NCs.

A simple PDMS-based microfluidic channel design that removes bubbles for long-term on-chip culture of mammalian cells

Abstract: This report shows methods to fabricate polydimethylsiloxane (PDMS) microfluidic systems for long-term (up to 10 day) cell culture. Undesired bubble accumulation in microfluidic channels abruptly changes the microenvironment of adherent cells and leads to the damage and death of cells. Existing bubble trapping approaches have drawbacks such as the need to pause fluid flow, requirement for external vacuum or pressure source, and possible cytotoxicity. This study reports two kinds of integrated bubble trap (IBT) which have excellent properties, including simplicity in structure, ease in fabrication, no interference with the flow, and long-term stability. IBT-A provides the simplest solution to prevent bubbles from entering microfluidic channels. In situ time-lapse imaging experiments indicate that IBT-B is an excellent device both for bubble trapping and debubbling in cell-loaded microfluidics. MC 3T3 E1 cells, cultured in a long and curved microfluidic channel equipped with IBT-B, showed high viability and active proliferation after 10 days of continuous fluid flow. The comprehensive measures taken in our experiments have led to successful long-term, bubble-free, on-chip culture of cells.

Carbon Nanotubes as a Framework for High-Aspect-Ratio MEMS Fabrication

Abstract: A class of carbon-nanotube (CNT) composite materials was developed to take advantage of the precise high-aspect-ratio shape of patterned vertically grown nanotube forests. These patterned forests were rendered mechanically robust by chemical vapor infiltration and released by etching an underlying sacrificial layer. We fabricated a diverse variety of functional MEMS devices, including cantilevers, bistable mechanisms, and thermomechanical actuators, using this technique. A wide range of chemical-vapor-depositable materials could be used as fillers; here, we specifically explored infiltration by silicon and silicon nitride. The CNT framework technique may enable high-aspect-ratio MEMS fabrication from a variety of materials with desired properties such as high-temperature stability or robustness. The elastic modulus of the silicon-nanotube and silicon nitride-nanotube composites is dominated by the filler material, but they remain electrically conductive, even when the filler (over 99% of the composite's mass) is insulating.

Fabrication of bulk nanocomposite magnets via severe plastic deformation and warm compaction

Abstract: We demonstrate that a SmCo/FeCo based hard/soft nanocomposite material can be fabricated by distributing the soft magnetic α-Fe phase particles homogeneously in a hard magnetic SmCo phase through severe plastic deformation. The soft-phase particle size can be reduced from micrometers to smaller than 15 nm upon deformation. Up to 30% of the soft phase can be incorporated into the composites without coarsening. A warm compaction process of the plastically deformed powder particles then produces bulk nanocomposite magnets of fully dense nanocomposites with energy product up to 19.2 MGOe owing to effective interphase exchange coupling, which makes this type of nanocomposite magnets suitable for high energy-density applications at high temperatures.

Prototypes for Bone Implant Scaffolds Designed via Topology Optimization and Manufactured by Solid Freeform Fabrication

Abstract: The linking of computational design with precision solid freeform fabrication has tremendous potential for producing tissue scaffolds with tailored properties We consider a new approach to optimizing the architecture of scaffolds based on jointly maximizing scaffold stiffness and diffusive transport in the interconnected pores The stiffness of the scaffolds is matched to that of bone by choosing a suitable scaffold porosity Moreover, the templates can be scaled to achieve target pore sizes whilst preserving their elastic and diffusive properties The resultant structures have two major design benefits First, the scaffolds do not have directions of low stiffness In contrast, the Young's modulus of conventional layered-grid designs can be 86% less under diagonally-aligned loads than under axis-aligned loads Second, the mass of the scaffold is used efficiently throughout the structure rather than being clumped in non load-bearing regions We fabricate prototypes of the implants using selective laser melting and test their elastic properties Excellent agreement between theory and experiment provides important confirmation of the viability of this route to scaffold design and fabrication

On the design and fabrication by two-photon polymerization of a readily assembled micro-valve

Abstract: This paper reports on the conceptual design and fabrication of a complex shape, readily assembled micro check valve using the two-photon polymerization technique. The material used for the fabrication of the valve is a zirconium containing organic–inorganic hybrid photosensitive sol-gel known to exhibit negligible distortion during photopolymerization. A preliminary computational fluid dynamics study has been carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design and the capability of an internal moving component to perform its intended function.

Micromechanics and Advanced Designs for Curved Photodetector Arrays in Hemispherical Electronic‐Eye Cameras

Abstract: The fabrication of a hemispherical electronic-eye camera with optimized designs based upon micromechanical analysis is reported. The photodetector arrays combine layouts with multidevice tiles and extended, non-coplanar interconnects to improve the fill factor and deformability, respectively. Quantitative comparison to micromechanics analysis reveals the key features of these designs. Color images collected with working cameras demonstrate the utility of these approaches.

Laser fabrication of 2D and 3D metal nanoparticle structures and arrays.

Abstract: A novel method for fabrication of 2D and 3D metal nanoparticle structures and arrays is proposed. This technique is based on laser-induced transfer of molten metal nanodroplets from thin metal films. Metal nanoparticles are produced by solidification of these nanodroplets. The size of the transferred nanoparticles can be controllably changed in the range from 180 nm to 1500 nm. Several examples of complex 2D and 3D microstructures generated form gold nanoparticles are demonstrated.

Micro-Optics Fabrication on Top of Optical Fibers Using Two-Photon Lithography

Abstract: We describe the fabrication of different micro-optical structures on top of optical fibers using two-photon polymerization. We show the convenience of this approach to quickly create generic three-dimensional shapes using a single setup by comparison to previous shape-dependent methods. A set of different structures, designed for different optical functions, are fabricated and characterized to demonstrate the versatility of this approach and their high optical quality.

Fabrication and characterization of CMOS-MEMS thermoelectric micro generators

Abstract: This work presents a thermoelectric micro generator fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 μV at the temperature difference of 1 K.

Lithography-free fabrication of high quality substrate-supported and freestanding graphene devices

Abstract: We present a lithography-free technique for fabrication of clean, high quality graphene devices. This technique is based on evaporation through hard Si shadow masks, and eliminates contaminants introduced by lithographical processes. We demonstrate that devices fabricated by this technique have significantly higher mobility values than those obtained by standard electron beam lithography. To obtain ultra-high mobility devices, we extend this technique to fabricate suspended graphene samples with mobilities as high as 120 000 cm 2 /(V·s).

Oriented Contraction: A Facile Nonequilibrium Heat-Treatment Approach for Fabrication of Maghemite Fiber-in-Tube and Tube-in-Tube Nanostructures

Abstract: We present a simple and effective nonequilibrium heat-treatment approach that allows for the facile fabrication of maghemite (γ-Fe(2)O(3)) fiber-in-tube and tube-in-tube nanostructures by heat-treating electrospun precursor fibers composed of polyvinylpyrrolidone (PVP) and iron citrate with a carefully devised heating rate (R). In this nonequilibrium heat-treatment procedure, R can be easily utilized to tune the temperature gradient established in the inner portion of the fibers and the difference between the cohesive force and the adhesive force at the interface layer between the inner gel and the dense rigid shell generated in situ by a high R. Therefore, the contraction direction of the precursor nanofibers and the final morphology of the resultant γ-Fe(2)O(3) fibers ranging from a simple tube to a fiber in tube to a tube in tube are realized for control. The nonequilibrium heat-treatment approach reported here can be readily extended to the fabrication of other materials with controllable interior structures by fast heating their corresponding gel precursors, which may be fabricated on the basis of electrospinning techniques and others. The resultant γ-Fe(2)O(3) fiber-in-tube and tube-in-tube nanostructures may have important applications in a number of areas, such as magnetic separable catalysts or catalyst supporting materials, sensors, absorbents, microreactors, and so forth, because of their structural characteristics and good magnetic properties.

Influence of microstructure and notch fabrication on impact bending properties of tungsten materials

Abstract: Refractory materials, in particular tungsten base materials are considered as primary candidates for high heat load applications in future nuclear fusion power plants. Promising design outlines make use of the high heat conductivity and strength of W-1%La2O3 (WL10) as structural material. Here, the lower temperature range is restricted by the transition to a steel part and the upper operation temperature limit is defined by the onset of recrystallization and/or loss of strength, respectively. The most critical issue of tungsten materials in connection with structural applications, however, is the ductile-to-brittle transition. Another problem consists in the fact that especially refractory alloys show a strong correlation between microstructure and their manufacturing history. Since mechanical properties are defined by the underlying microstructure, refractory alloys can behave quite different, even if their chemical composition is the same. Therefore, the fracture behavior of several tungsten based alloys was characterized by standard Charpy tests which have been performed up to 1100 °C in vacuum. Due to their fabrication history (powder mixing, pressing, sintering, rolling or swaging) all materials had specific microstructures which often led to typical delamination fractures. The influence of the microstructure characteristics like grain size, anisotropy, texture, or chemical composition as well as the effect of notch machining was investigated. All results are discussed and assessed with respect to the optimization of future component fabrication for high temperature nuclear fusion applications.

Efficient Blue‐Light‐Emitting Polymer Heterostructure Devices: The Fabrication of Multilayer Structures from Orthogonal Solvents

Abstract: [*] Prof. E. J. W. List, Dr. S. Sax, A. Neuhold NanoTecCenter Weiz Forschungsgesellschaft mbH Franz-Pichler-Straße 32, A-8160 Weiz (Austria) E-mail: list@ntc-weiz.at Prof. K. Müllen, N. Rugen-Penkalla Max Planck Institute for Polymer Research Ackermannweg 10, D-55128 Mainz (Germany) E-mail: muellen@mpip-mainz.mpg.de Prof. S. Schuh, Prof. E. Zojer, E. J. W. List Institute of Solid State Physics Graz University of Technology Petersgasse 16, A-8010 Graz (Austria)

The layer 0 inner silicon detector of the D0 experiment

Abstract: This paper describes the design, fabrication, installation and performance of the new inner layer called Layer 0 (L0) that was inserted in the existing Run IIa silicon micro-strip tracker (SMT) of the D0 experiment at the Fermilab Tevatron p¯p collider. L0 provides tracking information from two layers of sensors, which are mounted with center lines at a radial distance of 16.1 and 17.6 mm from the beam axis. The sensors and read-out electronics are mounted on a specially designed and fabricated carbon fiber structure that includes cooling for sensor and read-out electronics. The structure has a thin polyimide circuit bonded to it so that the circuit couples electrically to the carbon fiber allowing the support structure to be used both for detector grounding and a low impedance connection between the remotely mounted hybrids and the sensors.

Fabrication of 3D nanoimprint stamps with continuous reliefs using dose-modulated electron beam lithography and thermal reflow

Abstract: 3D electron beam lithography and thermal reflow were combined to fabricate structures with multilevel and continuous profiles. New shapes, smooth surfaces and sharp corners were achieved. By using exposure with variable doses, up to 20 steps were fabricated in a 500 nm thick resist with a lateral resolution of 200 nm. Steps were reflowed into continuous slopes by thermal post-processing, and were transferred into silicon substrates by proportional plasma etching. The method can be used for the fabrication of 3D nanoimprint stamps with both sharp features and continuous profiles.