Organic electrochemical transistors based on a dielectrophoretically aligned nanowire array

In this study, we synthesized an organic electrochemical transistor (OECT) using dielectrophoresis of a carbon nanotube-Nafion (CNT-Nafion) suspension. Dielectrophoretically aligned nanowires formed a one-dimensional submicron bundle between triangular electrodes. The CNT-Nafion composite nanowire bundles showed p-type semiconductor characteristics. The drain-source current decreased with increasing gate voltage. The nanowire bundles showed potential as pH sensor because the drain-source current ratio varied linearly according to the gate voltage in pH buffers

Design, Analysis, and Experimental Results of Micromachined Single-structure Triaxis Vibratory Gyroscope with Advanced Coupling Mechanism

In this work, a novel micromachined monolithic triaxis gyroscope with an advanced anchor mechanism is designed and its structural characteristics are analyzed. Micromachined gyroscopes are usually packed in small packages, causing a high squeeze film damping effect that reduces the quality factor of out-of-plane vibration, resulting in lowered out-of-plane sensitivity. The proposed gyroscope has a four-mass single structure wherein the opposing masses vibrate in the opposite direction perpendicular to the direction they face, with the help of 'tree-shaped' coupling springs. The simulated driving and x-, y-, and z-axis sensing resonant frequencies are 19946, 20227, 20294, and 20361 Hz, respectively. Also, the prototype of the gyroscope was fabricated and tested. It showed a driving Q-factor of 106 and a scale factor of 7 mV/deg/s.11Ysciescopu

Fabrication of Optical Switching Patterns with Structural Colored Microfibers

Structural color was generated using electrospinning and hydrothermal growth of zinc oxide (ZnO). An aligned seed layer was prepared by electrospinning, and the hydrothermal growth time control was adjusted to generate various structural colors. The structural color changed according to the angle of the incident light. When the light was parallel to the direction of the aligned nanofibers, no pattern was observed. This pattern is referred to as an "optical switching pattern." Replication using polydimethylsiloxane (PDMS) also enabled the generation of structural colors; this is an attractive approach for mass production. Additionally, the process is quite tunable because additional syntheses and etching can be performed after the patterns have been fabricated.11Ysciescopu

System Modeling of a MEMS Vibratory Gyroscope and Integration to Circuit Simulation

Recently, consumer applications have dramatically created the demand for low-cost and compact gyroscopes. Therefore, on the basis of microelectromechanical systems (MEMS) technology, many gyroscopes have been developed and successfully commercialized. A MEMS gyroscope consists of a MEMS device and an electrical circuit for self-oscillation and angular-rate detection. Since the MEMS device and circuit are interactively related, the entire system should be analyzed together to design or test the gyroscope. In this study, a MEMS vibratory gyroscope is analyzed based on the system dynamic modeling; thus, it can be mathematically expressed and integrated into a circuit simulator. A behavioral simulation of the entire system was conducted to prove the self-oscillation and angular-rate detection and to determine the circuit parameters to be optimized. From the simulation, the operating characteristic according to the vacuum pressure and scale factor was obtained, which indicated similar trends compared with those of the experimental results. The simulation method presented in this paper can be generalized to a wide range of MEMS devices111Ysciescopu

An underwater superoleophobic nanofibrous cellulosic membrane for oil/water separation with high separation flux and high chemical stability

Oil spills and an increasing demand for the treatment of industrial oily wastewater are driving the need for continuous large-scale oil/water separation processes. Herein, we report a nanofibrous cellulosic membrane (NFC membrane) for the continuous high-flux separation of large amounts of oil/water mixtures. The NFC membrane was fabricated using wet electrospinning, a facile yet effective method for stacking nanofibrous membranes with uniform porous structures on a substrate. Owing to its cellulosic nature, the membrane showed excellent underwater superoleophobicity along with robust chemical stability and was able to separate oil/water mixtures at efficiencies exceeding 99%. Repetitive oil/water separations could be performed using a single membrane, during which the oil content in the filtrate remained extremely low (30 kPa) that allowed not only gravity-driven but also pressure-driven separation of oil/water mixtures. The separation flux reached 120 000 L m−2 h−1 during pressure-driven separations, which is a very promising feature for actual applications such as the large-scale treatment of industrial oily wastewater.116Ysciescopu

Helical vortex formation in three-dimensional electrochemical systems with ion-selective membranes

The rate of electric-field-driven transport across ion-selective membranes can exceed the limit predicted by Nernst (the limiting current), and encouraging this “overlimiting” phenomenon can improve efficiency in many electrochemical systems. Overlimiting behavior is the result of electroconvectively induced vortex formation near membrane surfaces, a conclusion supported so far by two-dimensional (2D) theory and numerical simulation, as well as experiments. In this paper we show that the third dimension plays a critical role in overlimiting behavior. In particular, the vortex pattern in shear flow through wider channels is helical rather than planar, a surprising result first observed in three-dimensional (3D) simulation and then verified experimentally. We present a complete experimental and numerical characterization of a device exhibiting this recently discovered 3D electrokinetic instability, and show that the number of parallel helical vortices is a jump-discontinuous function of width, as is the overlimiting current and overlimiting conductance. In addition, we show that overlimiting occurs at lower fields in wider channels, because the associated helical vortices are more readily triggered than the planar vortices associated with narrow channels (effective 2D systems). These unexpected width dependencies arise in realistic electrochemical desalination systems, and have important ramifications for design optimization.United States. Advanced Research Projects Agency-Energy (Grant DE-AR0000294)Kuwait-MIT Center for Natural Resources and the EnvironmentNational Research Foundation of Korea (Grant 2012R1A2A2A06047424)Singapore-MIT Alliance for Research and Technolog

Fabrication of functional micro- and nanoneedle electrodes using a carbon nanotube template and electrodeposition

Carbon nanotube (CNT) is an attractive material for needle-like conducting electrodes because it has high electrical conductivity and mechanical strength. However, CNTs cannot provide the desired properties in certain applications. To obtain micro- and nanoneedles having the desired properties, it is necessary to fabricate functional needles using various other materials. In this study, functional micro- and nanoneedle electrodes were fabricated using a tungsten tip and an atomic force microscope probe with a CNT needle template and electrodeposition. To prepare the conductive needle templates, a single-wall nanotube nanoneedle was attached onto the conductive tip using dielectrophoresis and surface tension. Through electrodeposition, Au, Ni, and polypyrrole were each coated successfully onto CNT nanoneedle electrodes to obtain the desired properties