The use of carbon-based materials in electrochemical double-layer supercapacitors (EDLC) is currently being the focus of much research. Even though activated carbon (AC) is the state of the art electrode material, AC suffers from some drawbacks including its limited electrical conductivity, the need for a binder to ensure the expected electrode cohesion and its limited accessibility of its pores to solvated ions of the electrolyte. Owing to their unique physical properties, carbon nanotubes (CNTs) or graphene could overcome these drawbacks. It has been demonstrated that high specific capacitance could be obtained when the carbon accessible surface area of the electrode was finely tailored by using graphene combined with other carbonaceous nanoparticles such as CNTs12.In this work, to further increase the specific capacitance of the electrode, we have covalently grafted onto the surface of single-walled carbon nanotubes (SWCNTs), exfoliated graphite or graphene oxide (GO), anthraquinone (AQ) derivatives which are electrochemically active materials. The modified SWCNTs and graphene-like materials have been characterized by Raman spectroscopy, X-ray photoemission and cyclic voltammetry . Then suspensions based on mixtures of modified SWCNTs and modified graphene-like materials have been prepared and transformed into electrodes either by spray coating or by filtration. These electrodes have been characterized by SEM and by cyclic voltammetry in 0.1M H2S04 electrolyte.
This contribution deals with the fabrication of electrode and supercapacitor cell using a new dynamic air-brush deposition technique. This method allows to achieve extremely (ou highly) uniform mats with finely tuned thickness and weight in a completely reproducible way. Using this deposition technique, we have analyzed the effect of mixture of CNTs and graphene/graphite on the electrode and cell properties (energy, power and capacitance). using a mixture of 75% of graphene/graphite and 25% of CNTs we increased the power by a factor 2.5 compared to bare CNTs based electrodes. We also analyzed the effect of the weight firstly on the capacitance and specific energy and then on the specific power. We were able to reach a specific power of 200kW/Kg and a specific energy of 9.1Wh/Kg with an electrode having a surface of 2cm2 and a weight of 0.25mg composed by 50% of CNTs and graphene/graphite (using a common aqueous electrolyte). using our deposition technique we are able to achieve supercapacitors with ad-hoc characteristics simply modulating the weight and the concentration of the mixture in a completely reproducible way.
This contribution deals with Carbon Nanotubes Field Effect transistors (CNTFETs) based gas sensors fabricated using a
new dynamic spray based technique for SWCNTs deposition. This technique is compatible with large surfaces, flexible
substrates and allows to fabricate high performances transistors exploiting the percolation effect of the SWCNTs
networks achieved with extremely reproducible characteristics. Recently, we have been able to achieve extremely
selective measurement of NO2 , NH3 and DMMP using four CNTFETS fabricated using different metals as electrodes
(Pt, Au, Ti, Pd), exploiting the specific interaction between gas and metal/SWCNT junction. In this way we have identify
a sort of electronic fingerprinting of the gas. The time response is evaluated at less than 30sec and the sensitivity can
reach 20ppb for NO2, 100ppb for NH3 and 1ppm for DMMP (Di-Methyl-Methyl-Phosphonate).
Our study deals with the utilization of carbon nanotubes networks based transistors with different metal
electrodes for highly selective gas sensing. Indeed, carbon nanotubes networks can be used as semi
conducting materials to achieve good performances transistors. These devices are extremely sensitive to the
change of the Schottky barrier heights between Single Wall Carbon Nanotubes (SWCNTs) and drain/source
metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so
the bending and the height of the Schottky barrier at the contacts. Moreover each gas interacts specifically
with each metal identifying a sort of electronic fingerprinting. Using airbrush technique for deposition, we
have been able to achieve uniform random networks of carbon nanotubes suitable for large area applications
and mass production such as fabrication of CNT based gas sensors. These networks enable us to achieve
transistors with on/off ratio of more than 5 orders of magnitude. To reach these characteristics, the density of
the CNT network has been adjusted in order to reach the percolation threshold only for semi-conducting
nanotubes. These optimized devices have allowed us to tune the sensitivity (improving it) of our sensors for
highly selective detection of DiMethyl-Methyl-Phosphonate (DMMP, a sarin stimulant), and even volatile
drug precursors using Pd, Au and Mo electrodes.
This paper presents the design, fabrication and testing of capacitive
RF MEMS switches for microwave/mm- wave applications on high-resistivity silicon substrate or glass. The feasibility study and demonstrator fabrication of a new concept of reflector network using MEMS switch based phase-shifters concept for space antennas is presented. These switches can be accurately modeled using 3-D static solvers. The loss in the up-state position is equivalent to the CPW line loss and is 0.1-0.3 dB at 10-40 GHz. It is seen that the capacitance, inductance and series resistance can be accurately extracted from DC-40 GHz S-parameter measurements. The reflector array antennas utilization for phase control avoids the use of very expensive directive antennas and covers a very large frequencies range. We will deal with the configuration, the composition and
arrangement of MEMS switches, used to control the phase shift of the electromagnetic wave reflected by each elementary cell.
It has been shown that it is possible to produce highly selective and continuously tunable filters based on InP material using surface micro-machining. One interesting issue for this kind of device is NIR absorption spectroscopy for gas analysis. In this work, we present the design of a Resonant Cavity Enhanced tunable photodiode for operation around 1.6 micrometer near the C-H stretching frequency for organic molecules such as benzene. For this type of application, the required performances are a large tunability, a high selectivity, a weak temperature dependence and a constant absorption level over the tuning range. To meet these requirements the micro-system must be optimized from the optical and mechanical point of view. The RCE photodiode structure is composed of an air/InP bottom Bragg mirror and a dielectric top Bragg mirror. The cavity includes an air-gap and the InP layer containing a p.i.n. photodiode with absorption in a few strained InGaAs Quantum Wells (QWs). Tuning is obtained by actuating electrostatically the air micro-cavity thickness. A prospective device meeting the optical requirements has been designed. It is based on an absorption region composed of three InGaAS QWs conveniently located in the cavity standing wave pattern in order to optimize the resonant absorption over the tuning range. Optical simulation shows that an absorption level greater than 50% can be achieved. The temperature dependence of the resonance wavelength can be kept below 0.08 nm/(Delta) T(C degrees) at room temperature. The mechanical properties of the micromachined structure has been investigated using finite element analysis.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.