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Emergence of hierarchy during compression of quasi‐planar bilayers is preceded by a mode‐locked state during which the quasi‐planar form persists. Transition to hierarchy is determined entirely by geometrically observable parameters. This results in a universal transition phase diagram that enables one to deterministically tune hierarchy even with limited knowledge about material properties. [ABSTRACT FROM AUTHOR]

This paper provides engineering models of a simple and robust approach for creating electrical connections to silicon using reduced temperature (<200 °C substrate) soldering. This removes a significant hurdle to the fabrication of high performance, custom silicon piezoresistors. The approach focuses on reducing the resistance of diodes that are undergoing reverse bias behavior, commonly considered to be unacceptable for electrical connections. Reverse bias Schottky barrier analytical models based on quantum mechanical first principles are developed to explain how the behavior is affected by doping, soldering temperature, and geometry. This understanding is encapsulated within parametric models that enable rapid design and optimization of the electrical contacts to silicon. Using this model, one may design contacts for practical applications that do not require the conventional microfabrication processing or the high-temperature processing. Indium solder is found to be the best solder for this process, with ohmic contact resistances of \approx 1\Omega -cm ^{2} for \langle 110\rangle p-type wafers at 10^17 cm ^-3 doping. [ABSTRACT FROM AUTHOR]

This paper presents the design and characterization of a three-axis thermomechanical actuator-based endoscopic scanner for obtaining ex vivo two-photon images. The scanner consisted of two sub-systems: 1) an optical system (prism, gradient index lens, and optical fiber) that was used to deliver and collect light during imaging and 2) a small-scale silicon electromechanical scanner that could raster scan the focal point of the optics through a specimen. The scanner can be housed within a 7 mm Ø endoscope port and can scan at the speed of 3 kHz x 100 Hz × 30 Hz along three axes throughout a 125 × 125 × 100 μm3 volume. The high-speed thermomechanical actuation was achieved through the use of geometric contouring, pulsing technique, and mechanical frequency multiplication (MFM), where MFM is a new method for increasing the device cycling speed by pairing actuators of unequal forward and returning stroke speeds. Sample cross-sectional images of 15-μm fluorescent beads are presented to demonstrate the resolution and optical cross-sectioning capability of the two-photon imaging system. [ABSTRACT FROM AUTHOR]

Abstract: Early stage design of precision flexure systems that utilize strain-based displacement sensing is difficult due to the strong coupling between the mechanical and sensing subsystems. Traditional tools for flexure system and compliant mechanism synthesis are not capable of simultaneously optimizing the mechanical and sensing subsystems. The building block synthesis approach developed in this work is the only tool capable of designing compliant mechanisms with integrated strain based sensing. Building block modeling allows for rapid synthesis and vetting of concepts. This approach also allows the designer to determine concept feasibility, identify performance limits and tradeoffs, and obtain 1st order estimates of flexure geometry. In short, this method enables one to find an optimal design and set first order design parameters. The utility of the building block approach is detailed in a case study detailing the synthesis and modeling of three different one degree-of-freedom translational stages that are all derived from the series and parallel addition of fixed-guided cantilever beam building blocks. [Copyright &y& Elsevier]

Dip 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 µm⊃/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 through-put 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. [ABSTRACT FROM AUTHOR]

This paper covers the design, fabrication, and characterization of two-layer microcoils wherein an unannealed plasma-enhanced CVD Si02 functions as the insulator between silicon- and photoresist-molded copper coils. This design overcomes the thermal limitations placed upon coils that are embedded within polymer molds and thereby enables higher current carrying capability. The fabrication process is compatible with deep reactive-ion etching and may be used to integrate coils with flexures/compliant mechanisms. Thermal and mechanical limitations were determined experimentally and used to create design rules that limit the coil design space. The breakdown strength of the unannealed Si02 was measured at 4.6 MV/cm. Experiments show that coils with 40-jim pitch, 30 x 30-jim2 winding cross section, and Si02 thickness of 1 jtm may carry more than 1 A (larger than 10° Aim2) with less than 10 °C temperature change. These characteristics make the coils useful in small-scale actuators and power systems. [ABSTRACT FROM AUTHOR]

In this paper, we disclose how to contour the beams of microscale thermomechanical actuators (TMAs) in order to enhance the actuator's thermal and mechanical performance. In this approach, we vary the cross-section of the heated beams over the length of the beams. Using this approach, the stored strain energy and axial stiffness of the beam may be modified to achieve an optimized force-displacement relationship. Examples are provided to show that in some designs: 1) the maximum achievable thermal strain of a driving beam may be increased by 29%, 2) actuator stroke may be increased by a factor of four, and 3) identical force or displacement characteristics may be achieved with a 90% reduction in power. This paper presents the theory and models used to predict the thermal and mechanical behavior of the actuator. The theory and models were used to create a deterministic link between the actuator's design parameters and the actuator's performance characteristics. The theory and models were combined within a design tool that is posted at http://pcsl.mit.edu. The tool has been used to generate performance plots that enable designers to: 1) understand the quantitative relationships between design parameters and performance and 2) rapidly converge upon first-pass design parameters. [ABSTRACT FROM AUTHOR]

Dip 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%. [ABSTRACT FROM AUTHOR]

We present a method for selecting fabrication process parameters (temperature, catalyst film thickness, and hydrocarbon concentration) that may be used to grow multiwalled carbon nanotubes (CNTs) with desired outer diameter D and number of walls Nw. This capability enables the control of rigidity, which in turn makes it possible to control a CNT’s lateral vibration behavior and bending stiffness. A growth model was generated and used to link D and Nw to the process parameters. Experimental results showed that the models predicted D and Nw with less than 6% and 7% error, respectively. [ABSTRACT FROM AUTHOR]

The authors show that an elastic tube model of a (5,5) carbon nanotube predicts stretching and bending moduli that differ by 19%. This is due to (1) differing energy storage mechanisms in each mode and (2) the inability of the tube model to capture these effects. Conventional tube models assume a common energy storage mechanism in stretching and bending. They show that energy is stored primarily through bond stretching/rotation and bond torsion/van der Waals interactions in stretching and bending, respectively. This knowledge underscores the need to use different moduli to predict stretching, bending, and combined bending and stretching when using the tube model. [ABSTRACT FROM AUTHOR]

The authors report the behavior of a nanoscale parallel-guiding mechanism wherein the compliant components are single-walled carbon nanotubes. Parallel-guiding mechanisms are often the building blocks of macro- and microscale mechanical systems. The authors present results that provide insight into the performance of a parallel-guiding mechanism for nanoscale devices. The device exhibits a range over 75% of the device size, i.e., 5.5 nm, when actuated with 6.4 nN. Below 3.6 nN, displacements are due to bulk elastic bending of the nanotubes. Above 5.2 nN, displacements are governed by the hingelike bending of kinks in the nanotubes. van der Waals forces are shown to cause direction-dependent behavior. [ABSTRACT FROM AUTHOR]

This paper presents the design and fabrication of a multi-axis microelectromechanical system (MEMS) force sensor with integrated carbon nanotube (CNT)-based piezoresistive sensors. Through the use of proper CNT selection and sensor fabrication techniques, the performance of the CNT-based MEMS force sensor was increased by approximately two orders of magnitude as compared to current CNT-based sensor systems. The range and resolution of the force sensor were determined as 84 μN and 5.6 nN, respectively. The accuracy of the force sensor was measured to be better than 1% over the device’s full range. [ABSTRACT FROM AUTHOR]