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Advances in three-dimensional nanofabrication techniques have enabled the development of lightweight solids, such as hollow nanolattices, having record values of specific stiffness and strength, albeit at low production throughput. At the length scales of the structural elements of these solids-which are often tens of nanometers or smaller-forces required for elastic deformation can be comparable to adhesive forces, rendering the possibility to tailor bulk mechanical properties based on the relative balance of these forces. Herein, we study this interplay via the mechanics of ultralight ceramic-coated carbon nanotube (CNT) structures. We show that ceramic-CNT foams surpass other architected nanomaterials in density-normalized strength and that, when the structures are designed to minimize internal adhesive interactions between CNTs, more than 97% of the strain after compression beyond densification is recovered.

Purpose This paper aims to apply a robust methodology to establish relationships between user-configurable process parameters of commercial desktop stereolithography (SLA) printers and dimensional accuracy of a custom-designed test artifact. Design/methodology/approach A detailed response surface methodology study, Box–Behnken incomplete factorial design of four factors with three levels, was carried out to evaluate process performance of desktop SLA printers. The selected factors were as follows: printing orientation angle in x-direction, printing orientation angle in y-direction, position on build platform in spatial x-coordinate, position on build tray in spatial y-coordinate and layer thickness. The proposed artifact was designed to include 12 feature groups including thin walls, holes, bosses, bridges and overhangs. Two responses were associated with the features: the dimensional deviation according to the designed value and the minimum feature size. Findings Layer thickness was the most significant factor in 70% of the analyzed responses. For example, measurement deviation was reduced about 90% when cylindrical holes were printed with the lowest layer thickness. Further, in many cases, dimensional deviation was minimized for features at the center of the platform, where the beam cures the resin in a straight line. However, at distant positions, accuracy could be improved by compensating for beam deviation by changing the object orientation angle. Originality/value The findings of this study can serve, both generally and specifically, for SLA designers and engineers who wish to optimize printing process variables and feature location to achieve high-dimensional accuracy and further understand the many coupled considerations among part design, build configuration and process performance.

At an estimated cost of $8 billion annually in the United States, revision total joint replacement surgeries represent a substantial financial burden to the health care system. Fixation failures such as implant loosening and mechanical instability at the cement-to-bone interface are the main causes of long-term implant failure. Early and accurate diagnosis of cement-bone interface failure is critical to develop therapeutic strategies and reduce the risk of delayed revision surgery. Unfortunately, prevailing imaging modalities such as plain radiographs struggle to detect the precursors of implant failure and are often interpreted incorrectly. Our team has recently shown that modification of poly(methyl methacrylate) (PMMA) bone cement with low concentrations of conductive fillers makes it piezoresistive and therefore self-sensing. By electrical impedance tomography (EIT) it is possible to monitor load transfer across the PMMA using real-time electrical measurements, which are physiologically benign and would ultimately be cost-effective in a clinical setting. Herein, we demonstrate the use of machine learning with EIT in order to precisely characterize model failure events. In phantom tests, we introduce three defect types: loosening, vertical cracks, and horizontal cracks. We show that implant defect type can be classified with greater than 95% accuracy by combining principal component analysis (PCA) coupled with the k-nearest neighbor (KNN) algorithm and a two layer feed-forward neural network with three hidden neurons . These preliminary results show that the combination of smart materials, EIT, and machine learning may be a powerful tool for predicting and diagnosing failure in joint replacements.

The growing demand for electric vehicles and portable devices has brought significant attention to the scalability, recyclability, and economics of both traditional and emerging battery technologies. Lithium-ion batteries (LIB) are approaching their theoretical energy density yet remain the most widespread and promising technology for the next 5-10 years, as alternative (e.g., Li-metal) chemistries and solid-state architectures are still in relatively early stages of commercial scale-up. An alternative route to improve LIB performance and therefore increase energy density, is to redesign the cell geometry to incorporate thick electrodes. Batteries with thick planar (2D) electrodes suffer from power limitations and capacity loss due to increased Li-ion diffusion distances and tortuosity. 3D electrode designs compensate for this weakness by providing micro-scale channels within the electrode to enable rapid charge transport. Prototype LIBs using 3D electrodes have been fabricated using a wide variety of laboratory techniques (e.g., lithography, imprinting, direct-ink writing), which have afforded study of diverse geometries (e.g., pillar arrays, lattices, interpenetrating structures) and active materials (e.g., Si, Sn, carbon-based, lithium transition metal oxides). However, these methods do not have requisite scalability or compatibility with industrial LIB processing techniques, which demand: (1) integration with cost-effective metal substrates as current collectors; (2) compatibility with commodity anode/cathode materials and electrolytes; and (3) high-rate continuous production and cell assembly. Moreover, the materials used in 3D electrodes must be mechanically robust, electrically conductive, patterned at the microscale level, and have sufficient porosity to accommodate expansion and contraction upon charging and discharging. We are developing thick 3D “honeycomb” battery electrodes using patterned, vertically aligned carbon nanotubes (VA-CNTs) as current collectors. CNTs are widely known to have high thermal and electrical conductivities, and to be mechanically durable. VA-CNTs (“forests”) form by self-organization of CNTs during chemical vapor deposition (CVD) on substrates using common hydrocarbon sources (e.g., C2H2, C2H4). However, well-established CNT growth techniques utilize rigid non-conductive substrates, such as silicon wafers, necessitating an additional transfer step to a suitable substrate. Recently, we translated these insights from CNT growth on silicon wafer substrates to thin metal foils (Cu) suitable for battery electrode fabrication, using optimized in-furnace moisture conditions, and a thin-film interface that forms high-density nanoparticles upon annealing, and prevents diffusion of Cu that is known to poison CNT growth. The resulting CNT forests can reach up to 500 μm thickness and can be patterned to have regular hole arrays with feature sizes as small as ~5 μm. Thick composite electrodes are then created by coating CNT forests with Si thin films by CVD. The inherent nanoporosity of the CNT forests (>95%) allows for precursor diffusion into the entirety of the forest cross-section. The CVD conditions are tuned to create dense electrodes with tailored Si loading ranging from ~10 to ~90 at.%. Half-cells using monolithic and patterned Si-CNT electrodes (~200 μm tall), Li-metal foil and a liquid electrolyte/separator combination are cycled over a range of currents, demonstrating electronic connection between the deposited Si and Cu foil via the aligned CNTs. At low currents (C/5) these electrodes demonstrate large gravimetric capacities, indicating the lithiation of CNTs beneath the deposited Si. We will also investigate cycling performance at high currents (>5C) and perform post-mortem characterization of the Si-CNT interface to study how the CNTs and their patterning govern the stability of the electrode. Future work will look to optimize electrode performance by manipulating the geometric parameters of the CNT forests and assess the economics of CNT-based electrode manufacturing at commercial scales.

In many physical processes, including cloud electrification, electrospray, and demulsification, droplets and bubbles are exposed to electric fields and may either remain whole or burst in response to electrical stresses. Determining the stability limit of a droplet exposed to an external electric field has been a long-standing mathematical challenge, and the only analytical treatment to date is an approximate calculation for the particular case of a free-floating droplet. Here we demonstrate, experimentally and theoretically, that the stability limit of a conducting droplet or bubble exposed to an external electric field is described by a power law with broad generality that, in practice, applies to the cases in which the droplet or bubble is pinned or sliding on a conducting surface or free floating. This power law can facilitate the design of devices for liquid manipulation via a simple formula that captures the parameter range of bubbles and droplets that can be supported on electrified surfaces.

Powder bed additive manufacturing (AM) processes, including binder jetting (BJAM) and powder bed fusion (PBF), can manufacture complex three-dimensional components from a variety of materials. A fundamental understanding of the spreading of thin powder layers is essential to develop robust process parameters for powder bed AM, and to assess the influence of powder feedstock characteristics on the subsequent process outcomes. Toward meeting these needs, this work presents the design, fabrication, and qualification of a testbed for modular, mechanized, multi-layer powder spreading. The testbed is designed to replicate the operating conditions of commercial AM equipment, yet features full control over motion parameters including the translation and rotation of a roller spreading tool, and precision motion of a feed piston and the build platform. The powder spreading mechanism is interchangeable and therefore can be customized, including the capability for dispensing of fine, cohesive powders using a vibrating hopper. Validation of the resolution and accuracy of the machine and its subsystems, as well as the spreading of exemplary layers from a range of powder sizes typical of BJAM and PBF processes, are described. The precision engineered testbed can therefore enable the optimization of powder spreading parameters for AM and correlation to build process parameters in future work, as well as exploration of spreading of specialized powders for AM and other techniques.

Aseptic loosening, or loss of implant fixation, is a common complication following total joint replacement. Revision surgeries cost the healthcare system over $8 billion annually in the US. Despite the prevalence of aseptic loosening, timely and accurate detection remains a challenge because traditional imaging modalities such as plain radiographs struggle to reliably detect the early stages of implant loosening. Motivated by this challenge, we present a novel approach for in vivo monitoring and failure detection of cemented joint replacements. Poly(methyl methacrylate) (PMMA) bone cement is modified with low volume fractions of chopped carbon fiber (CF) to impart piezoresistive-based self-sensing. Electrical impedance tomography (EIT) is then used to detect and monitor load-induced deformation and fracture of CF/PMMA in a phantom tank. We therefore show that EIT indeed is able to adeptly detect loading force on a prosthetic surrogate, distinguish between increasing load magnitudes, detect failure of implant fixation, and even distinguish between cement cracking and cement de-bonding. Because EIT is a low-cost, physiologically benign, and potentially real-time imaging modality, the feasibility study herein presented has potential to transform the standard of care for post-operative monitoring of implant conditions. Beyond clinical relevance, this technique could positively impact orthopedic researchers by providing, via in vivo monitoring, insight into the factors that initiate aseptic loosening., Comment: 8 pages, 7 figures

Applications of carbon nanotubes (CNTs) in flexible and complementary metal-oxide-semiconductor (CMOS)-based electronic and energy devices are impeded due to typically low CNT areal densities, growth temperatures that are incompatible with device substrates, and challenges in large-area alignment and interconnection. A scalable method for continuous fabrication and transfer printing of dense horizontally aligned CNT (HA-CNT) ribbon interconnects is presented. The process combines vertically aligned CNT (VA-CNT) growth by thermal chemical vapor deposition, a novel mechanical rolling process to transform the VA-CNTs to HA-CNTs, and adhesion-controlled transfer printing without needing a carrier film. The rolling force determines the HA-CNT packing fraction and the HA-CNTs are processed by conventional lithography. An electrical resistivity of 2 mOmega . cm is measured for ribbons having 800-nm thickness, while the resistivity of copper is 100 times lower, a value that exceeds most CNT assemblies made to date, and significant improvements can be made in CNT structural quality. This rolling and printing process could be scaled to full wafer areas and more complex architectures such as continuous CNT sheets and multidirectional patterns could be achieved by straightforward design of the CNT growth process and/or multiple rolling and printing sequences.

This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 106 particles cm−3. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm−3 depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.

The exceptional electronic, thermal, and mechanical properties of carbon nanotubes (CNTs) have motivated extensive research on their manufacturing and applications. At bulk scales, there is particular interest in property enhancements by adding CNTs to polymers to make composite materials. Most work on CNT-based composites presented in the literature to date has focused on dispersion of single- or multiwalled CNTs (SWNTs or MWNTs) in the matrix; however, bulk CNTs embedded in a polymeric matrix tend to form aggregates that are not only poorly adhered to the matrix but also concentrate stresses, compromising the effect of the CNTs as reinforcement. [1] On the other hand, establishing order and alignment among CNTs within a composite matrix offers significant further potential to harness the properties of individual CNTs at bulk scales by realizing the anisotropic properties of CNTs in desired directions, and by enabling packing and dispersion of CNTs at much higher volume fractions than in tangled configurations. In this work, CNT–polymer composites are manufactured by wetting as-grown arrays of vertically aligned CNTs rapidly and effectively (lack of voids) using off-the-shelf polymers. The wetting process not only preserves the alignment of the CNTs, but also allows the controlled manufacturing of nanocomposite test structures. Direct characterization of the mechanical properties of the nanocomposite structures is also presented in this work. The mechanical-reinforcement results support the feasibility of using these CNTarrays in large-scale hybrid advanced composite architectures reinforced with aligned CNTs. Such composites will also benefit from multifunctional property (e.g., electrical conductivity) enhancements owing to the aligned CNTs.

The increasing demand for wearable electronic devices has made the development of highly elastic strain sensors that can monitor various physical parameters an essential factor for realizing next generation electronics. Here, we report an ultrahigh stretchable and wearable device fabricated from dry-spun carbon nanotube (CNT) fibers. Stretching the highly oriented CNT fibers grown on a flexible substrate (Ecoflex) induces a constant decrease in the conductive pathways and contact areas between nanotubes depending on the stretching distance; this enables CNT fibers to behave as highly sensitive strain sensors. Owing to its unique structure and mechanism, this device can be stretched by over 900% while retaining high sensitivity, responsiveness, and durability. Furthermore, the device with biaxially oriented CNT fiber arrays shows independent cross-sensitivity, which facilitates simultaneous measurement of strains along multiple axes. We demonstrated potential applications of the proposed device, such as strain gauge, single and multiaxial detecting motion sensors. These devices can be incorporated into various motion detecting systems where their applications are limited to their strain.

In spite of much research progress in the science and synthesis of carbon nanotubes (CNTs), control over the location and orientation of CNTs on substrates remains a major challenge. A key breakthrough was the synthesis of vertically aligned CNT (VA-CNT) arrays using thermal chemical vapor deposition (CVD) and plasma-enhanced CVD, where the CNTs self-orient perpendicular to the substrate surface due to initial crowding and continue to grow upward in this direction. These CNT arrays have wide-ranging applications, including membranes, heat dissipation, electrical interconnects, and nanoelectronics. The catalysts for synthesis of VACNTs are commonly prepared by sputtering or evaporating a thin metal film onto a substrate, which dewets to form catalyst nanoparticles at an elevated temperature prior to growth. While these catalysts are easily prepared and patterned by shadow masking or lithography, these approaches are not easily able to create nanocluster catalysts that have monodisperse diameters and quantifiable areal densities. In thin metal films, both the nanocluster size and areal density are coupled to the film thickness, and the annealing procedure affects the size, density, and the chemical state of the nanoclusters. Recently, Huh et al. demonstrated a route for controlling the density of CNT growth using varying densities of colloidal cobalt nanoparticles; however, due to nanoparticle coalescence their route does not enable precise quantification of nanocluster areal density and leads to a broad distribution of CNT diameters. Zhang et al. also recently demonstrated the control of CNT growth by varying the density of Co–Mo nanoparticles, although their route is unable to independently vary the diameter and the areal density of nanoparticles. We employ a methodology for synthesizing iron oxide nanoclusters that utilizes micelles formed by the amphiphilic block copolymer, polystyrene-b-poly(acrylic acid) (PS-bPAA). This catalyst system has significant value because it enables the creation of nanocluster arrays of a chosen metal species, with independent control of the nanocluster diameter and areal density. In previous work, nanocluster diameters were varied between 5 and 16 nm and the areal density was varied from 6.0 × 10 to 1 × 10 cm, although variation outside of these ranges is easily accessible. At higher areal densities the nanoclusters are hexagonally ordered. Further, as we have presented separately, the nanocluster arrays can be patterned on the micrometer length scale using microcontact printing. Here, we utilize this system to create arrays of uniform-diameter iron oxide nanoclusters, with quantifiable areal densities that can be varied over more than an order of magnitude. We achieve vertical CNT growth from our catalyst system through appropriate selection of the substrate, catalyst preparation procedure, and reaction conditions. To the best of our knowledge, our work is the first example of vertical growth of CNTs from a block-copolymer-based catalyst. Because this catalyst system allows for precise quantification of the nanocluster areal density, we can estimate the percentage of nanoclusters that nucleate the growth of a CNT. By uniformly varying the areal density of iron oxide nanoclusters on the substrate surface, we manipulate the morphology of the CNT film from a tangled and sparse arrangement of individual CNTs, through a transition region with locally bunched and self-aligned CNTs, to rapid growth of thick vertical CNT films. The procedure for synthesizing the iron oxide nanocluster arrays utilized spherical micelles formed by PS-b-PAA in toluene, which were loaded with FeCl3, and then spin-cast onto a substrate (see Experimental Section). The polymer thin film was then treated in oxygen plasma to remove the organic components, leaving an iron oxide nanocluster array, as shown in Figure 1A. Previous studies have demonstrated that the iron oxide nanocluster structure is Fe2O3. [22,25] The molecular weight and metal-loading ratios of Figure 1A led to iron oxide nanocluster arrays with diameters of 16 ± 1.6 nm that were arranged in a quasihexagonal array with an areal density of 6.0 × 10 cm. The root-mean-square roughness of the nanocluster arrays was 2.2 nm, as determined from using atomic force microscopy (AFM). C O M M U N IC A TI O N S

We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al(2)O(3)) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the PDMS features. The PDMS stamp is then put in contact with a substrate, and uniaxial compressive stress is applied to transfer the micellar thin film from the PDMS stamp onto the substrate in a defined pattern. The polymer is then removed by oxygen plasma etching to leave a patterned iron oxide nanocluster array on the substrate. Using these catalysts, we achieve patterned vertical growth of multiwalled CNTs, where the CNTs maintain the fidelity of the patterned catalyst, forming high-aspect-ratio standing structures.

We demonstrate that a film of vertically aligned multiwall carbon nanotubes (CNTs) can exert mechanical energy as it grows, and in our experiments the average force output is approximately 0.16 nN per CNT, for CNTs having an outer diameter of 9 nm and five walls. The film thickness after a fixed growth time and the alignment of CNTs within the film decrease concomitantly with increasing pressure which is applied by placing a weight on the catalyst substrate prior to growth, and CNTs grown under applied pressure exhibit significant structural faults. The measured mechanical energy density of CNT growth is significantly less than the energies of primary steps in the CNT formation process yet, based on the film volume, is comparable to the energy density of muscle and based on the volume of CNTs is comparable to hydraulic actuators. We utilize this principle to fabricate three-dimensional structures of CNTs which conform to the shape of a microfabricated template. This technique is a catalytic analogue to micromolding of polymer and metal microstructures; it enables growth of nanostructures in arbitrarily shaped forms having sloped surfaces and nonorthogonal corners and does not require patterning of the catalyst before growth.

We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt transitions between areas of micrometer-thick tangled CNT films and millimeter-scale aligned CNT structures are manipulated by changing the duration of pretreatment by H2/Ar prior to introduction of C2H4 and by changing the configuration of the substrate sample in the furnace tube. This demonstrates that the flow profile over the sample mediates the supply of reactants to the catalyst and that pretreatment using H2 significantly affects the initial activity of the catalyst.

Carbon nanotubes (CNTs) and nanofibres (CNFs) are grown on bulk-micromachined silicon surfaces by thermal and plasma-enhanced chemical vapour deposition (PECVD), with catalyst deposition by electron beam evaporation or from a colloidal solution of cobalt nanoparticles. Growth on the peaked topography of plasma-etched silicon 'micrograss' supports, as well as on sidewalls of vertical structures fabricated by deep-reactive ion etching demonstrates the performance of thermal CVD and PECVD in limiting cases of surface topography. In thermal CVD, uniform films of tangled single-walled CNTs (SWNTs) coat the structures despite oblique-angle effects on the thickness of the catalyst layers deposited by e-beam evaporation. In PECVD, forests of aligned CNFs protrude from areas which are favourably wet by the colloidal catalyst, demonstrating selective growth based on surface texture. These surface preparation principles can be used to grow a wide variety of nanostructures on microstructured surfaces having arbitrary topography, giving substrates with hierarchical microscale and nanoscale surface textures. Such substrates could be used to study cell and neuronal growth, influence liquid–solid wetting behaviour, and as functional elements in microelectronic and micromechanical devices.

We discuss growth of high-quality carbon nanotube (CNT) films on bare and microstructured silicon substrates by atmospheric pressure thermal chemical vapor deposition (CVD), from a Mo/Fe/Al 2 O 3 catalyst film deposited by entirely electron beam evaporation. High-density films having a tangled morphology and a Raman G/D ratio of at least 20 are grown over a temperature range of 750–900 °C. H 2 is necessary for CNT growth from this catalyst in a CH 4 environment, and at 875 °C the highest yield is obtained from a mixture of 10%/90% H 2 /CH 4 . We demonstrate for the first time that physical deposition of the catalyst film enables growth of uniform and conformal CNT films on a variety of silicon microstructures, including vertical sidewalls fabricated by reactive ion etching and angled surfaces fabricated by anisotropic wet etching. Our results confirm that adding Mo to Fe promotes high-yield SWNT growth in H 2 /CH 4 ; however, Mo/Fe/Al 2 O 3 gives poor-quality multi-walled CNTs (MWNTs) in H 2 /C 2 H 4 . An exceptional yield of vertically-aligned MWNTs grows from only Fe/Al 2 O 3 in H 2 /C 2 H 4 . These results emphasize the synergy between the catalyst and gas activity in determining the morphology, yield, and quality of CNTs grown by CVD, and enable direct growth of CNT films in micromachined systems for a variety of applications.

While kinematic couplings are frequently used as components of repeatable interfaces in ideal environments, their use in heavily loaded industrial interfaces is less frequent, as previous studies have validated couplings mostly under modest loads and controlled environmental conditions. On the other hand, the performance of heavily loaded industrial equipment, such as robots used in automotive production, could benefit from highly repeatable interfaces for assembly and replacement of modules. A series of tests was conducted to assess the industrial repeatability performance of large kinematic couplings on an ABB 6400R industrial robot. The interfaces for two of the more frequently detached interfaces-the robot base to the factory floor interface and the robot wrist interface-were tested. For both interfaces, replacements for the existing pin joint interfaces were designed using two forms of kinematic couplings-a three-pin coupling and a canoe-ball coupling. During industrial testing, measurements were taken for each coupling form on the base and wrist interfaces. Both laboratory and industrial experiments demonstrated that the installation procedure is almost as important as the form of coupling itself and that properly mounted kinematic couplings can improve the repeatability of machine interfaces by up to 90%. Laboratory measurements provided best-case canoeball coupling repeatability on the order of 0.1 Nm and threepin coupling repeatability of 1 μm. In industrial trials, the canoe-ball coupling repeatability was 0.05 mm for the wrist interface and 0.10 mm for the base interface. The three-pin coupling was capable of 0.11 mm repeatability for the base interface, and limited testing for the wrist interface indicates possible 0.08 mm repeatability.

The design and prototype tests of a segmented and shielded instrumentation structure, based on tube modules connected by canoe ball type kinematic couplings, are presented with application to a high-precision microscope for biological science experiments. The segmented tube design is shown to be significantly less sensitive to deformation from uneven thermal disturbances than a single tube structure. The gaps between the tube segments relieve thermal strains and restrict axial heat conduction, and the large-radius kinematic couplings provide high thermal resistance interconnects without significantly degrading structural stiffness. Simulation results, based on two- and three-dimensional models of heat conduction, are verified with experimental measurements of prototype structures and are used to predict the dependence of the tilt error on the geometry, boundary conditions, and material properties of the tubular segments. Adding layers of low-cost foam insulation and thin metal shielding to the walls of the structure further improves performance. Kinematic couplings could allow the structure to be disassembled and reassembled without re-calibration, and thus, pre-calibrated tube modules with different components could be easily and quickly interchanged between experiments.

The deterministic nature of kinematic couplings enables closed-form characterization of interchangeability error, parametrized in terms of the magnitudes of manufacturing tolerances in the interface manufacturing and assembly processes. A process is suggested for calibrating kinematic couplings to reduce the interchangeability error, based on measurement of the contact points and calculation of a transformation matrix between the interface halves. A Monte Carlo analysis is developed and validated for predicting interchangeability of canoe ball kinematic couplings, and repeatability measurements and interchangeability simulation results are presented for kinematic coupling interfaces for the base and wrist of an industrial robot. Total mounting error, defined as the sum of the interchangeability and repeatability errors, appears to be dependent to first order only on the interface repeatability and the error of the interface calibration procedure.

A fundamentally precise and simple linear motion axis design is discussed where the attractive force from the linear motor is used to preload a carriage supported by six rigidly attached porous carbon air bearings. The air bearings are assembled by vacuuming the pads to two orthogonal planes, positioning the carriage above the pads, and then injecting epoxy between the bearings and the carriage. Control of flatness tolerances of the bearings and planes permits over-constraint of the carriage by the bearings, which leads to a high degree of accuracy and moment load capacity via elastic averaging. Good dynamic stiffness is also obtained because of large bearing area and squeezed-film damping. The two orthogonal planes represent an accurate and cost effective geometry that can be created to guide linear motion; and by placing the open-face iron-core motor at the desired position and angle with respect to the bearings, preload forces with equal or otherwise desired relative magnitudes are obtained. Because the attractive force is typically 3–5 times the axial force generated by the motor, the system is inherently stable even in the presence of large externally applied moments that might otherwise induce excessive pitch, yaw, or roll errors.

The skins of many plants and animals have intricate microscale surface features that give rise to properties such as directed water repellency and adhesion, camouflage, and resistance to fouling. However, engineered mimicry of these designs has been restrained by the limited capabilities of top–down fabrication processes. Here we demonstrate a new technique for scalable manufacturing of freeform microstructures via strain-engineered growth of aligned ​carbon nanotubes (CNTs). Offset patterning of the CNT growth catalyst is used to locally modulate the CNT growth rate. This causes the CNTs to collectively bend during growth, with exceptional uniformity over large areas. The final shape of the curved CNT microstructures can be designed via finite element modeling, and compound catalyst shapes produce microstructures with multidirectional curvature and unusual self-organized patterns. Conformal coating of the CNTs enables tuning of the mechanical properties independently from the microstructure geometry, representing a versatile principle for design and manufacturing of complex microstructured surfaces., United States. Defense Advanced Research Projects Agency (HR0011-10-C-0192), United States. Air Force Office of Scientific Research (Young Investigator Program FA9550-11-1-0089)

The work function of tetrahedral amorphous carbon (ta-C) has been measured by Kelvin probe to lie in the range 4–5 eV, irrespective of its sp3 content or nitrogen addition. This implies that the surface barrier to emission is dominant and that emission changes caused by sp3 bonding or nitrogen addition are not directly due to changes in work function. Hydrogen, oxygen, and argon plasma treatments are all found to increase the emission of a-C, but hydrogen and argon treatments are found to reduce the work function while oxygen treatment increases it. Detailed studies of the surface with varying plasma treatment conditions suggest that the changes in emission arise mainly from changes in the surface microstructure, such as the formation of sp2 regions within the sp3 bulk. The need for local field enhancement mechanisms to account for emission over the sizeable barrier is emphasized, which may arise from local chemical nonhomogeneity, or formation of nanometer-size sp2 clusters embedded in an sp3 matrix.

A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600–700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.

Carbon nanotubes (CNTs) are promising for microsystems applications, yet few techniques effectively enable integration of CNTs with precise control of placement and alignment of the CNTs at sufficiently high densities necessary for compelling mechanical or electrical performance. This paper explores new methods for scalable integration of dense, horizontally aligned (HA) CNTs with patterned electrodes. Our technique involves the synthesis of vertically aligned (VA) CNTs directly on a conductive underlayer and subsequent mechanical transformation into HA-CNTs, thus making electrical contact between two electrodes. We compare elasto-capillary folding and mechanical rolling as methods for transforming VA-CNTs, which lead to distinctly different HA-CNT morphologies and potentially impact material and device properties. As an example application of this novel CNT morphology, we investigate fabrication of electrically addressable CNT-C60 hybrid thin films that we previously demonstrated as photodetectors. We synthesize these assemblies by crystallizing C60 from dispersion on HA-CNT thin-film scaffoldings. HA-CNTs fabricated by rolling result in relatively low packing density, so C60 crystals embed inside the HA-CNT matrix during synthesis. On the other hand, C60 crystallization is restricted to near the surface of HA-CNT films made by the elasto-capillary process.

We present a direct-write technique for assembly of microscale 3D colloidal crystals on substrates. We use a custombuilt high-resolution liquid manipulation system to dispense colloidal suspensions through a capillary tip. Using this system, we establish a liquid bridge between the capillary tip and a temperature-controlled substrate, initiating crystal growth upward from the substrate. We demonstrate construction of cone-shaped and tower structures by controlling the dynamic shape of the liquid meniscus during crystal precipitation. Interplay between lateral capillary forces and granular cohesion governs assembly. Finally, we show that confinement of the meniscus on microfabricated template features enables assembly of discrete particle clusters.

Plants as well as other biological organisms achieve directed movements by fibres that constraint and direct the isotropic expansion of a matrix material. In order to mimic these actuators, complex arrangements of rigid fibres must be achieved, which is challenging, especially at small scales. In this paper, a new method to organize carbon nanotubes (CNTs) into complex shapes is employed to create a framework for hydrogel infiltration. These CNT frameworks can be realized as iris, needle and bridge architectures, and after hydrogel infiltration, they show directed actuation in response to water uptake. Finally, we show how the latter can be employed as a novel hygroscopic sensor. ispartof: pages:1717-1720 ispartof: SENSORS AND ACTUATORS A-PHYSICAL pages:1717-1720 ispartof: 16th International Conference On Solid-State Sensors, Actuators and Microsystems location:Beijing date:5 Jun - 9 Jun 2011 status: published

Capillary forming of carbon nanotubes (CNTs) enables the fabrication of unique 3D microstructures over large areas. In this paper we focus on the simulation as well as on the integration of these structures in MEMS devices. We developed finite element models (FEM) that enables qualitative prediction of shape transformations caused by capillary forming; and show how capillary formed CNT structured can be integrated with conventional lithographic processing for patterning of polymers and metals in concert with CNTs ispartof: pages:2718-2721 ispartof: SENSORS AND ACTUATORS A-PHYSICAL issue:16 pages:2718-2721 ispartof: 16th International Conference On Solid-State Sensors, Actuators and Microsystems location:Beijing date:5 Jun - 9 Jun 2011 status: published

Recent studies show that carbon nanotubes (CNTs) can be used as temperature sensors, and offer great opportunities towards extreme miniaturization, high sensitivity, low power consumption, and rapid response. Previous CNT based temperature sensors are fabricated by either dielectrophoresis or piece-wise alignment of read-out electronics around randomly dispersed CNTs. We introduce a new deterministic and parallel microsensor fabrication method based on the self-assembly of CNTs into three-dimensional microbridges. We fabricated prototype microbridge sensors on patterned electrodes, and found their sensitivity to be better than −0.1 %/K at temperatures between 300K and 420K. This performance is comparable to previously published CNT based temperature sensors. Importantly, however, our research shows how unique sensor architectures can be made by self-assembly, which can be achieved using batch processing rather than piece-wise assembly.

To understand the mechanism of electron field emission from diamond-like carbon, tetrahedral amorphous carbon (ta-C) films were subjected to Ar, H2, and O2 plasma treatments to change their surface condition and were deposited on substrates of different work function. The threshold fields and current densities for undoped ta-C are found to be significantly improved by the plasma treatments, largely due to an increase in emission site density, while little dependence was found on work function of substrate. This suggests that the main barrier to emission from ta-C is at the front surface.

High volume fraction aligned carbon nanotube (CNT) nanocomposite specimens are fabricated using mechanical densification of CNT forests and capillarity-induced wetting of the forests with several thermoset polymers. Such nanocomposites approach the ideal morphology of collimated aligned fiber systems used in aerospace composites, and have long been expected to exhibit substantial engineering property improvements over existing systems. Polymers used are unmodified and include two aerospace-grade complex thermosets and a UV-curing thermoset used in microfabrication. Mechanical densification of the CNT forests prior to polymer introduction results in uniform nanocomposites. High volume fraction (to ~20%) CNT forests are effectively wet by the thermosets studied. Modulus, hardness, and electrical resistivity are characterized as a function of volume fraction for one of the epoxy systems. Multifunctional properties (modulus, hardness, and electrical conductivity) of the nanocomposites are strongly influenced by CNT volume fraction. Such specimens can be used to explore nano-scale interaction effects such as CNT- CNT contact effects on thermal and electrical conductivities.

*† ‡ § ** , This work presents the fabrication and characterization of three hybrid multiscale advanced composite materials. Long (>20 micron), aligned carbon nanotubes (CNTs) are placed at the interface of existing advanced composite plies and used as a reinforcement and to enhance electrical properties of the laminate. Three fabrication routes utilizing aligned CNTs at ply interfaces are presented: transplantation of CNT forests between prepreg carbon/epoxy plies, transfer of aligned CNTs and layup between woven carbon fiber plies that are subsequently infused to form a laminate, and in situ growth of aligned CNTs on the interior (and surface) of alumina fiber woven cloth prior to hand layup. Aerospace-grade thermoset epoxies, without modification, are noted to wet and penetrate the unfunctionalized aligned CNT forests, which is consistent with initial studies on solely CNT-polymer interactions. In all the fabrication routes, aligned CNTs are observed at the interface after laminate fabrication. Both mechanical (interlaminar) and multifunctional (electrical) property modifications are noted for the laminates containing CNTs. Significant interlaminar property enhancement has been observed and the mechanisms of this reinforcement are investigated via optical and scanning electron microscopy. Further improvements in the fabrication routes are discussed, and further testing of additional laminate-level property enhancements are suggested. Nomenclature

Rapid continuous thermal control of chemical reactions such as those for chemical vapor deposition (CVD) growth of nanotubes and nanowires cannot be studied using traditional reactors such as tube furnaces, which have large thermal masses. We present the design, modeling, and verification of a simple, low-cost reactor based on resistive heating of a suspended silicon platform. This system achieves slew rates exceeding 100 degrees C/s, enabling studies of rapid heating and thermal cycling. Moreover, the reaction surface is available for optical monitoring. A first-generation CVD apparatus encapsulates the heated silicon platform inside a sealed quartz tube, and initial experiments demonstrate growth of films of tangled single-wall and aligned multiwall carbon nanotubes using this system. The reactor can be straightforwardly scaled to larger or smaller substrate sizes and may be extended for a wide variety of reactions, for performing in situ reaction diagnostics, for chip-scale growth of nanostructures, and for rapid thermal processing of microelectronic and micromechanical devices.

A series of tetrahedrally bonded carbon (ta-C) films have been produced using a Filtered Cathodic Vacuum Arc System. The threshold field and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical undoped ta-C films have a threshold field of 15–20V/μm and optimally nitrogen doped films exhibit threshold fields as low as ∼ 5 V/μm. Current densities of typically 10-4 A/cm2 at an applied field of 20V/micron were also obtained.

Vertically aligned carbon nanotube (CNT) arrays are grown on a moving substrate, demonstrating continuous growth of nanoscale materials with long-range order. A cold-wall chamber with an oscillating moving platform is used to locally heat a silicon growth substrate coated with an Fe/Al2O3 catalyst film for CNT growth via chemical vapor deposition. The reactant gases are introduced over the substrate through a directed nozzle to attain high-yield CNT growth. Aligned multi-wall carbon nanotube arrays (or 'forests') with heights of approximately 1 mm are achieved at substrate speeds up to 2.4 mm s(-1). Arrays grown on moving substrates at different velocities are studied in order to identify potential physical limitations of repeatable and fast growth on a continuous basis. No significant differences are noted between static and moving growth as characterized by scanning electron microscopy and Raman spectroscopy, although overall growth height is marginally reduced at the highest substrate velocity. CNT arrays produced on moving substrates are also found to be comparable to those produced through well-characterized batch processes consistent with a base-growth mechanism. Growth parameters required for the moving furnace are found to differ only slightly from those used in a comparable batch process; thermal uniformity appears to be the critical parameter for achieving large-area uniform array growth. If the continuous-growth technology is combined with a reaction zone isolation scheme common in other types of processing (e.g., in the manufacture of carbon fibers), large-scale dense and aligned CNT arrays may be efficiently grown and harvested for numerous applications including providing interlayers for advanced composite reinforcement and improved electrical and thermal transport.

The interaction, or wetting, of long aligned carbon nanotube (CNT) forests with off-the-shelf (no solvent added) commercial thermoset polymers is investigated experimentally. A technique for creating vertically aligned CNT composite microstructures of various shapes is presented. The effective wetting of the forests, as evidenced by a lack of voids, by three polymers with widely varying viscosities supports the feasibility of using CNT forests in large-scale hybrid advanced composite architectures. Among various routes identified for the polymer to penetrate the forest, capillarity-driven wetting along the CNT axis is the preferred route. Aligned CNT microstructures are useful in many applications including test structures for direct mechanical and multifunctional property characterization of the aligned CNT?polymer composite materials.