21 research outputs found
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><sub>c</sub>, depending
sensitively on the disorder induced carrier density (<i>n</i><sub>c</sub>). Even for good quality graphene, the <i>n</i><sub>c</sub> can be quite high (∼10<sup>12</sup> cm<sup>–2</sup>) 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><sub>c</sub> 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<sub>2D</sub>/I<sub>G</sub> values (up to 12) with narrow 2D width (16–24 cm<sup>–1</sup>). The observed <i>T</i><sub>c</sub> values
seem to go hand in hand with the Raman I<sub>2D</sub>/I<sub>G</sub> values; a multilayer with
mean I<sub>2D</sub>/I<sub>G</sub> value of 4.6 showed a <i>T</i><sub>c</sub> of
180 K, while that with mean I<sub>2D</sub>/I<sub>G</sub> of 4.9 showed lower a <i>T</i><sub>c</sub> of 160 K. Further, another multilayer with even higher
mean I<sub>2D</sub>/I<sub>G</sub> 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<sup>–1</sup>) and <i>I</i><sub>2D</sub>/<i>I</i><sub>G</sub> 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