Integration of multifunctional carbon nanotube and graphene for sensing and actuation devices

Carbon nanotubes' multifunctional properties make them promising for the sensing applications. Vapor sensing using different types of chemiresistive materials in which the resistance change of CNT-polymer or surface-functionalized MWCNTs composites is monitored. A comparison of sensor materials based on carbon black (CB) and CNTs as the conducting species is explored. Carbonnanotubes show an improved discriminability as the conducting element for the composite thin-film array-based vapor-sensing. We explore various parameters such as the resistance change, mass uptake, signal vs. vapor concentration, partition coefficients, and discrimination performance when such sensors are exposed to a variety of organic analytes. We also exploit functionalized CNT sensors to detect various gases as well toxic elements.

Chemical vapor detection using carbon nanotube bundles

The electrical transport behavior of carbon nanotubes (CNTs) upon exposure to organic analytes (namely ethanol, benzene, acetone and toluene) has shown a nonlinear current–voltage characteristics revealing a power law dependence of the differential conductivity on the applied bias voltage. Moreover, suppression of differential conductivity at zero bias is found to be dependent on different selective analytes. The power law exponent values have been monitored before, during and after exposure to the chemicals, which reveal a reversible change in the number of electron conducting channels. Therefore, the reduction in the number of conductive paths can be attributed to the interaction of the chemical analyte on the CNT surfaces, which causes a decrease in the differential conductivity of the CNT sample. These results demonstrate chemical selectivity of CNTs due to varying electronic interaction with different chemical analytes.

Reference: Gowda P.; Suri A.; Reddy S. K.; Misra A. "Chemical vapor detection using nonlinear electrical properties of carbon nanotube bundles", Nanotechnolgy, 2014, 25, 025708

Study of ultra-high actuation in a bulk carbon nanotube structure

Electric-field induced nonlinear actuation behavior is studied in a bulk nanotube (CNT) structure under ambient conditions. Completely recoverable and non-degradable actuation over several cycles of electric-field is measured. Asymmetric and polarity independent displacement corresponding up to an axial strain of 14% is measured upon application of a low strength electric field of 4.2 kV/m in the axial direction. However, a much lower strain of ∼1% is measured in the radial (or, transverse) direction. Furthermore, the electric field induced actuation increases by more than a factor of 2 upon impregnating the CNT cellular structure with copper oxide nano-particles.

Reference: Gowda P.; Kumar P.; Tripathi R.; Misra A. "Electric field induced ultra-high actuation in a bulk carbon nanotube structure", Carbon, 2014, 67, 546.

Morphology dependent photocurrent generation in few-layer graphene photodetectors

A novel approach for achieving an enhanced photoresponse in a few layer graphene (FLG) based photodetector is realized by introducing defect sites in the FLG. Fabrication induced wrinkle formation in graphene presented a four-fold enhancement in the photocurrent when compared to unfold FLG. Interestingly, it was observed that the addition of few multiwalled carbon nanotubes to an FLG improves the photocurrent by two-fold along with a highly stable response as compared to FLG alone.

Reference: Gowda P.; Sakorikar T.; Reddy S. K.; Ferry D. B.; Misra A. "Defect induced enhancement/quenching control of photocurrent in few layer graphene photodetector”, ACS Applied Materials & Interfaces, 2014, 6, 7485.

Nonlinear optical absorption in graphene infrared photodetector

Photoresponse of the graphene photodetector elucidated a strong dependence on optical parameters such as angle of optical incidence and incident power under an infrared exposure at room temperature. A sinusoidal dependence of photoresponse on incidence angle is revealed that has not been realized so far. Nonlinear dependence of charge carrier generation on incident power revealed contributing to the nonlinear photoresponse. A deviation is observed at higher incident power due to the induction of thermal effects in the graphene lattice. This work demonstrates a tunablility of the graphene photodetector under a systematic variation of both the parameters.

Reference: Gowda P.; Mahopatra D. R.; Misra A. “Nonlinear optical absorption in graphene infrared photodetector”, Nanotechnology (accepted), article no: NANO-102916.

In-situ monitoring of electro-thermo-mechanical behavior of multifunctional hybrid nano-materials

Multifunctional carbon nanotubes (CNTs) present their potential for monitoring strain induced deformation, using change in their electrical resistance. An integrated assembly of carbon nanotube in polymer also been utilized to provide flexible electrodes embedded in aligned CNTs. Rapid response of the composite structure offers fabrication of functional strain gauge, where size ranging from micron to macro scale.

Reference: Misra A.; Raney J.R.; Craig A.C.; De Nardo L.; Daraio C. "Synthesis and characterization of carbon nanotube-polymer multilayer structures", ACS Nano 5 , 7713, 2011.

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