1,720,986 research outputs found
Integrated visual nanometric three dimensional positioning and inspection in the automated assembly of AFM probe arrays
Get PDFSUMMARY This paper presents the design of a monocular three dimensional artificial vision system attached to a 20x microscope lens for precision and microsystems applications. Possible uses in assembly include: positioner calibration, sensor-based part handling, positioning, and inspection in the nanometric range. The developed image acquisition method – along one direction (in steps of 100 nm), the depth-from-focus algorithm and subpixel interpolation (of 5 acquisitions for concurrent localization and inspection), allow to overcome the physical optics limitation achieving a resolution under 200 nm. The vision strategy and algorithms, described in the paper, have been validated by handling an AFM probe array by a micropositioner
Understanding the drivers for the development of design rules for the synthesis of cylindrical flexures
No full textCylindrical flexures (CFs), defined as flexures with only one finite radius of curvature loaded normal to the plane of curvature, present an interesting research direction in compliant mechanisms. CFs are constructed out of a cylindrical stock which leads to geometry, manufacturability, and compatibility advantages. Synthesis rules must be developed to design these new systems effectively. Current knowledge in flexure design pertains to straight-beam flexures or curved flexures loaded along the plane of curvature. CFs present a challenge because their mechanics differ from those of straight beams, and although their modelling has been researched thoroughly it has yet to be distilled into element and system creation rules. This paper uses models and finite element analysis to demonstrate that current design rules for straight-beam flexures are insufficient and inadequate for the design of CF systems. The presented discussion will show that CFs differ both at the element and systems levels, and therefore future research will focus on developing the three components of the building block approach: (i) reworking of element mechanics models to reveal the parameters which cause the kinematics of the curved beam to differ from those of the straight beam, (ii) development of a visual stiffness representation, and (iii) formation of system creation rules.National Science Foundation (U.S.). Graduate Research Fellowship ProgramLincoln Laborator
Nanomanufacturing Methods for the Reduction of Noise in Carbon Nanotube-Based Piezoresistive Sensor Systems
Get PDFCarbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper, we will demonstrate several nanomanufacturing methods that can be used to decrease noise in the CNT-based sensor system without reducing the sensor's strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system, it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental effects. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. The optimal annealing conditions were determined using a design-of-experiments (DOE). Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost 3 orders of magnitude and increase the dynamic range of the sensors by 48 dB
A surface diffusion model for Dip Pen Nanolithography line writing
No full textDip Pen Nanolithography is a direct write process that creates nanoscale dots and lines. Models typically predict dot and line size via assumption of constant ink flow rate from tip to substrate. This is appropriate for dot writing. It is however well-known, though models rarely reflect, that the ink flow rate depends upon writing speed during line writing. Herein, we explain the physical phenomenon that governs line writing and use this to model tip-substrate diffusion in line writing. We accurately predict (i) the increase in flow rate with writing speed and (ii) line width within 12.5%
Design of a Compact Biaxial Tensile Stage for Fabrication and Tuning of Complex Micro- and Nano-scale Wrinkle Patterns
Get PDFWrinkling of thin films is a strain-driven process that enables scalable and low-cost fabrication of periodic micro- and nano-scale patterns. In the past, single-period sinusoidal wrinkles have been applied for thin-film metrology and microfluidics applications. However, real-world adoption of this process beyond these specific applications is limited by the inability to predictively fabricate a variety of complex functional patterns. This is primarily due to the inability of current tools and techniques to provide the means for applying large, accurate, and nonequal biaxial strains. For example, the existing biaxial tensile stages are inappropriate because they are too large to fit within the vacuum chambers that are required for thin-film deposition/growth during wrinkling. Herein, we have designed a compact biaxial tensile stage that enables (i) applying large and accurate strains to elastomeric films and (ii) in situ visualization of wrinkle formation. This stage enables one to stretch a 37.5 mm long film by 33.5% with a strain resolution of 0.027% and maintains a registration accuracy of 7 μm over repeated registrations of the stage to a custom-assembled vision system. Herein, we also demonstrate the utility of the stage in (i) studying the wrinkling process and (ii) fabricating complex wrinkled patterns that are inaccessible via other techniques. Specifically, we demonstrate that (i) spatial nonuniformity in the patterns is limited to 6.5%, (ii) one-dimensional (1D) single-period wrinkles of nominal period 2.3 μm transition into the period-doubled mode when the compressive strain due to prestretch release of plasma-oxidized polydimethylsiloxane (PDMS) film exceeds ∼18%, and (iii) asymmetric two-dimensional (2D) wrinkles can be fabricated by tuning the strain state and/or the actuation path, i.e., the strain history. Thus, this tensile stage opens up the design space for fabricating and tuning complex wrinkled patterns and enables extracting empirical process knowledge via in situ visualization of wrinkle formation
Characterization of the Dip Pen Nanolithography Process for Nanomanufacturing
No full textDip pen nanolithography (DPN) is a flexible nanofabrication process for creating 2-D nanoscale features on a surface using an “inked” tip. Although a variety of ink-surface combinations can be used for creating 2-D nanofeatures using DPN, the process has not yet been characterized for high throughput and high quality manufacturing. Therefore, at present it is not possible to (i) predict whether fabricating a part is feasible within the constraints of the desired rate and quality and (ii) select/design equipment appropriate for the desired manufacturing goals. Herein, we have quantified the processing rate, tool life, and feature quality for DPN line writing by linking these manufacturing metrics to the process/system parameters. Based on this characterization, we found that (i) due to theoretical and practical constraints of current technology, the processing rate cannot be increased beyond about 20 times the typical rate of ∼1 μm2 /min, (ii) tool life for accurate line writing is limited to 1–5 min, and (iii) sensitivity of line width to process parameters decreases with an increase in the writing speed. Thus, we conclude that for a high throughput and high quality system, we need (i) parallelization or process modification to improve throughput and (ii) accurate fixtures for rapid tool change. We also conclude that process control at high speed writing is less stringent than at low speed writing, thereby suggesting that DPN has a niche in high speed writing of narrow lines.National Science Foundation (U.S.) (Grant No. 0914790
An Automated Stage for Scalable Imprinting of DNA Nanowires Based on a Self-Aligning Technique
No full textMolecular combing is an established technique for aligning DNA nanowires on a surface. When performed on micro-patterned surfaces, this technique can be used to reliably align and stretch DNA nanowires across micro pillars. Imprinting of these aligned DNA nanowires is an affordable technique for fabrication of arrays of nano-scale channels across micro-scale reservoirs. In the past, DNA combing and imprinting (DCI) have been performed manually to fabricate polymer chips that are used in biomedical applications such as gene therapy and drug delivery studies. Automation of the DCI process is necessary to improve the yield and to scale-up production for these applications. However, existing automated techniques are not appropriate for DNA nano wire imprinting because these techniques cannot handle (i) fragile stamps and (ii) individual chip scale stamps of size ∼1 cm2. Herein, we present the design, fabrication and performance evaluation of an imprinting stage that enables (i) handling fragile stamps via low-cost equipment and (ii) production scale-up via simultaneous handling of multiple stamps. The stage is based on a self-aligning imprinting technique that passively aligns a stamp parallel to the substrate thereby enabling simultaneous imprinting of multiple stamps via a single stage. This self-alignment technique minimizes nano wire breakage by ensuring (i) minimal in-plane stamp motion during imprinting and (ii) that the contact forces do not exceed the weight of the stamp. Based on this technique we have designed/fabricated a stage that can simultaneously handle three stamps and is capable of further scale-up. The stage consists of a movable platform that is mounted on linear bearings and is actuated via a stepper motor. Stamps are loaded onto a holder that is mounted on the movable platform via kinematic couplings. This allows one to rapidly attach and detach the holder from the stage and also makes it possible to handle fragile stamps during loading/unloading. Imprinting of DNA nanowires with a manual stage has demonstrated the feasibility of the self-alignment scheme. Experiments that were performed to test the alignment capability of the stage verify that conformal stamp contact can be achieved across all three stamps even in the presence of an angular misalignment of 5obetween the stamp and the glass slide. This ability to simultaneously align multiple stamps is a critical step in being able to scale-up and fully automate the DCI process. Copyright © 2012 by ASME.National Science Foundation (U.S.) (Grant No. 0914790
Soft Origami: Classification, Constraint, and Actuation of Highly Compliant Origami Structures
Get PDFHerein, we discuss the folding of highly compliant origami structures—“Soft Origami.” There are benefits to be had in folding compliant sheets (which cannot self-guide their motion) rather than conventional rigid origami. Example applications include scaffolds for artificial tissue generation and foldable substrates for flexible electronic assemblies. Highly compliant origami has not been contemplated by existing theory, which treats origami structures largely as rigid or semirigid mechanisms with compliant hinges—“mechanism-reliant origami.” We present a quantitative metric—the origami compliance metric (OCM)—that aids in identifying proper modeling of a homogeneous origami structure based upon the compliance regime it falls into (soft, hybrid, or mechanism-reliant). We discuss the unique properties, applications, and design drivers for practical implementation of Soft Origami. We detail a theory of proper constraint by which an ideal soft structure's number of degrees-of-freedom may be approximated as 3n, where n is the number of vertices of the fold pattern. Buckling and sagging behaviors in very compliant structures can be counteracted with the application of tension; we present a method for calculating the tension force required to reduce sagging error below a user-prescribed value. Finally, we introduce a concept for a scalable process in which a few actuators and stretching membranes may be used to simultaneously fold many origami substructures that share common degrees-of-freedom.United States. Air Force Office of Scientific Research (Grant 1332249)National Science Foundation (U.S.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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