We report that the flow of a liquid on single-walled carbon nanotube bundles induces a voltage in the sample along the direction of the flow. The voltage that was produced fit a logarithmic velocity dependence over nearly six decades of velocity. The magnitude of the voltage depended sensitively on the ionic conductivity and on the polar nature of the liquid. Our measurements suggest that the dominant mechanism responsible for this highly nonlinear response involves a direct forcing of the free charge carriers in the nanotubes by the fluctuating Coulombic field of the liquid flowing past the nanotubes. We propose an explanation based on pulsating asymmetric ratchets. Our work highlights the device potential for nanotubes as sensitive flow sensors and for energy conversion.
New experimental results, and a plausible theoretical understanding thereof, are presented for the flow-induced currents and voltages observed in single-walled carbon nanotube samples. In our experiments, the electrical response was found to be sublinear -nearly logarithmic -in the flow speed over a wide range, and its direction could be controlled by an electrochemical biasing of the nanotubes. These experimental findings are inconsistent with the conventional idea of a streaming potential as the efficient cause. Here we present Langevin-equation based treatment of the nanotube charge carriers, assumed to be moving in the fluctuating field of ions in the flowing liquid. The resulting "Doppler-shifted" force-force correlation, as seen by the charge carriers drifting in the nanotube, is shown to give a sublinear response, broadly in agreement with experiments.
Nanotechnology
Nanotechnology V 1505Carbon Nanotube Flow Sensors. -The flow of a polar liquid over single-walled carbon nanotube bundles induces a voltage in the sample along the direction of the flow. The observed data are fitted empirically to a logarithmic dependence of the voltage on the flow velocity over nearly six decades of velocity. The magnitude of the voltage induced along the nanotube depends significantly on the ionic strength of the flowing liquid. The potential for nanotubes as sensitive flow sensors is highlighted. It is believed that this sensor can be scaled down to length dimensions of the order of micrometers, making it usable in very small liquid volumes. The sensor also has high sensitivity at low velocities and a fast response time better than 1 ms. The nanotubes could also be used to make a voltage and current source in a flowing liquid environment, which may have interesting biomedical applications. -(GHOSH, S.; SOOD*, A. K.; KUMAR, N.; Science (Washington, D.
MnO 3 show insulator-metal transitions on the passage of small electrical currents. That such an electric-field-induced transition occurs even in Y 0.5 Ca 0.5 MnO 3 where the charge-ordered state is not affected by magnetic fields is noteworthy. The transition is attributed to the depinning of the randomly pinned charge solid. These materials also exhibit an interesting memory effect probably due to the randomness of the strength as well as the position of the pinning centers.
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