Ultrafast response humidity sensor using supramolecular nanofibre and its application in monitoring breath humidity and flow

Measuring humidity in dynamic situations calls for highly sensitive fast response sensors. Here we report, a humidity sensor fabricated using solution processed supramolecular nanofibres as active resistive sensing material. The nanofibres are built via self- assembly of donor and acceptor molecules (coronene tetracarboxylate and dodecyl methyl viologen respectively) involved in charge transfer interactions. The conductivity of the nanofibre varied sensitively over a wide range of relative humidity (RH) with unprecedented fast response and recovery times. Based on UV-vis, XRD and AFM measurements, it is found that the stacking distance in the nanofibre decreases slightly while the charge transfer band intensity increases, all observations implying enhanced charge transfer interaction and hence the conductivity. It is demonstrated to be as a novel breath sensor which can monitor the respiration rate. Using two humidity sensors, a breath flow sensor was made which could simultaneously measure RH and flow rate of exhaled nasal breath. The integrated device was used for monitoring RH in the exhaled breath from volunteers undergoing exercise and alcohol induced dehydration

Dynamic self-assembly of charge-transfer nanofibers of tetrathiafulvalene derivatives with F<inf>4</inf>TCNQ

One-dimensional charge-transfer nanostructures were constructed by the supramolecular coassembly of amphiphilic (Amph-TTF) and hydrophobic (TDD-TTF) tetrathiafulvalene (TTF) donor derivatives with the acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), in appropriate solvent composition mixtures. Microscopic analyses show that TDD-TTF retains its self-assembled fibrillar morphology even in the charge-transfer state, whereas Amph-TTF undergoes a spherical to nanorod transition upon coassembly. Time-dependent optical spectroscopy studies have shown a spontaneous change in molecular organization in TDD-TTF-based donor-acceptor costacks, which suggests a dynamic behavior, in contrast to the kinetically stable amphiphilic TTF assemblies. We have also tried to get an insight into the observed time-dependent change in molecular packing of these nanostructures through spectroscopic analyses by commenting on whether the TTF-TCNQ pair is cofacially arranged or present in the classical herringbone (orthogonal) fashion. Furthermore, our two-probe electrical measurements showed that these charge-transfer fibers are conducting. A supramolecular approach that yields 1D charge-transfer nanostructures of donor and acceptor molecules will be an alternative to existing crystalline substances with high conductivity and hence can be a viable tool for nanoelectronics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Low cost, rapid synthesis of graphene on Ni: an efficient barrier for corrosion and thermal oxidation

Graphene because of its inert and impermeable nature holds a great promise as a protective coating against corrosion and oxidation. It is envisioned that graphene coated metals will be increasingly used in metal and electronic industries. To date, mainly expensive chemical vapor deposition methods are being employed for its synthesis over large area involving hydrogen at high reaction temperatures. Here we report, a simple and rapid method of Joule heating a Ni foil coated with naphthalene in rotary vacuum to produce graphene without hydrogen gas. The graphene thus grown protects the Ni surface against corrosion and oxidation even at elevated temperatures. This synthetic approach has a great potential for widespread use as it is low cost and adaptable to metal surfaces of complex curvatures

High-mobility field effect transistors based on supramolecular charge transfer nanofibres

Self-assembled charge transfer supramolecular nanofibres of coronene tetracarboxylate (CS) and dodecyl substituted unsymmetric viologen derivative (DMV) behave as active channel in field effect transistors exhibiting high mobility. These devices work in ambient conditions and can regenerate in the presence of a single drop of water. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A Supramolecular Nanofiber-Based Passive Memory Device for Remembering Past Humidity

Memorizing the magnitude of a physical parameter such as relative humidity in a consignment may be useful for maintaining recommended conditions over a period of time. In relation to cost and energy considerations, it is important that the memorizing device works in the unpowered passive state. In this article, we report the fabrication of a humidity-responsive device that can memorize the humidity condition it had experienced while being unpowered. The device makes use of supramolecular nanofibers obtained from the self-assembly of donor–acceptor (D–A) molecules, coronene tetracarboxylate salt (CS) and dodecyl methyl viologen (DMV), respectively, from aqueous medium. The fibers, while being highly sensitive to humidity, tend to develop electrically induced disorder under constant voltage, leading to increased resistance with time. The conducting state can be regained via self-assembly by exposing the device to humidity in the absence of applied voltage, the extent of recovery depending on the magnitude of the humidity applied under no bias. This nature of the fibers has been exploited in reading the humidity memory state, which interestingly is independent of the lapsed time since the humidity exposure as well as the duration of exposure. Importantly, the device is capable of differentiating the profiles of varying humidity conditions from its memory. The device finds use in applications requiring stringent condition monitoring

High-mobility field effect transistors based on supramolecular charge transfer nanofibres

Self-assembled charge transfer supramolecular nanofibres of coronene tetracarboxylate (CS) and dodecyl substituted unsymmetric viologen derivative (DMV) behave as active channel in field effect transistors exhibiting high mobility. These devices work in ambient conditions and can regenerate in the presence of a single drop of water

Intrinsic Nature of Graphene Revealed in Temperature-Dependent Transport of Twisted Multilayer Graphene

Graphene in its purest form is expected to exhibit a semiconducting to metallic transition in its temperature-dependent conductivity as a result of the interplay between Coulomb disorder and phonon scattering, the transition temperature, <i>T</i>_c, depending sensitively on the disorder induced carrier density (<i>n</i>_c). Even for good quality graphene, the <i>n</i>_c can be quite high (∼10¹² cm^–2) and the transition temperature may be placed well above the ambient, practically rendering it to be only semiconducting over a wide range of temperature. Here we report an experimental study on the transport behavior of twisted multilayer graphene (tMLG) exhibiting <i>T</i>_c well below the ambient temperature. The graphene layers in these tMLG are highly decoupled with one another due to the angular rotation among them; as a result, they exhibit very high Raman I_2D/I_G values (up to 12) with narrow 2D width (16–24 cm^–1). The observed <i>T</i>_c values seem to go hand in hand with the Raman I_2D/I_G values; a multilayer with mean I_2D/I_G value of 4.6 showed a <i>T</i>_c of 180 K, while that with mean I_2D/I_G of 4.9 showed lower a <i>T</i>_c of 160 K. Further, another multilayer with even higher mean I_2D/I_G value of 6.9 was metallic down to 5 K, indicating a very low disorder. The photoresponse behavior also corroborates well with the transition in transport behavior

Highly Decoupled Graphene Multilayers: Turbostraticity at its Best

The extraordinary properties of graphene are truly observable when it is suspended, being free from any substrate influence. Here, a new type of multilayer graphene is reported wherein each layer is turbostratically decoupled, resembling suspended graphene in nature, while maintaining high degree of 2D crystallinity. Such defect-free graphene multilayers have been made over large areas by Joule heating of a Ni foil coated with a solid hydrocarbon. Raman spectra measured on thick flakes of turbostratically single layer graphene (T-SLG) (100–250 nm) have shown characteristics similar to suspended graphene with very narrow 2D bands (∼16 cm^–1) and <i>I</i>_2D/<i>I</i>_G ratios up to 7.4, importantly with no D band intensity. Electron diffraction patterns showed sets of diffraction spots spread out with definite angular spacings, reminiscent of the angular deviations from the AB packing which are responsible for keeping the layers decoupled. The <i>d</i>-spacing derived from X-ray diffraction was larger (by ∼0.04 Å) compared to that in graphite. Accordingly, the <i>c</i>-axis resistance values were three orders higher, suggesting that the layers are indeed electronically decoupled. The high 2D crystallinity observed along with the decoupled nature should accredit the observed graphene species as a close cousin of suspended graphene