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.
Here we present our on-going efforts toward the development of stable ballasted carbon nanotube-based field emitters
employing hydrothermally synthesized zinc oxide nanowires and thin film silicon-on-insulator substrates. The
semiconducting channel in each controllably limits the emission current thereby preventing detrimental burn-out of
individual emitters that occurs due to unavoidable statistical variability in emitter characteristics, particularly in their
length. Fabrication details and emitter characterization are discussed in addition to their field emission performance. The
development of a beam steerable triode electron emitter formed from hexagonal carbon nanotube arrays with central
focusing nanotube electrodes, is also described. Numerical ab-initio simulations are presented to account for the
empirical emission characteristics. Our engineered ballasted emitters have shown some of the lowest reported lifetime
variations (< 0.7%) with on-times of < 1 ms, making them ideally-suited for next-generation displays, environmental
lighting and portable x-rays sources.
Graphene has been given great attention to overcome current physical limits in electronic devices and its synthesis routes
are developing rapidly. However, graphene film manufacturing is still hindered by either low throughput or low material
quality. Here, we present a low temperature PE-CVD assisted graphene growth process on nickel thin films deposited on silicon oxide. Furthermore, our process leads to the formation of two separated graphene films, one at the nickel surface and the other at the Ni/SiO2 interface. A mixture of methane and hydrogen was employed as carbon precursor and activated by DC plasma. We found that the number of graphene layers on top of nickel can be controlled by carbon exposure time, from 1 to around 10 layers. Further annealing process of samples allowed us to achieve improved graphene films by the dissolution and segregation-crystallization process.
In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine the growth of silicon
nanowires (SiNWs). High-density arrays of parallel, straight and organized SiNWs have been realized, by Hot Wire
Chemical Vapor Deposition (HW-CVD) growth process inside PAA templates with electrodeposited copper as catalyst.
The PAA was made by the anodization of an aluminium layer, followed by the catalysts electrodeposition at the bottom
of the pores. Subsequently, SiNWs were grown in a modified HW-CVD reactor with SiH4 as the precursor gas. The
morphology and the structure of the wires have been investigated by SEM and TEM, and their collective electrical
behavior has been characterized with a 2-probes device.
We successfully synthesized organized Carbon nanotubes (CNTs) and Silicon Nanowires (SiNWs) arrays using LPAA.
This approach can yield very dense assemblies of nano-objects with a planar-type organization compatible with existing
tools inherited from advanced microelectronic processes and adapted to electronic devices as field effect transistors,
interconnects, sensors, etc. CNTs/SiNWs were grown using Hot-filament Chemical Vapor Deposition (HFCVD) within
lateral-type porous anodic alumina. We demonstrate that the pulsed electrodeposition of metal nanoparticles to be further
used as catalysts inside the membranes requires specific thinning and pore widening process to remove the alumina
barrier layer located at the bottom of the pores. The growth of CNTs was found to strongly depend on the
electrodeposition conditions as well as on the CVD parameters. In addition, we found that introducing atomic hydrogen
(generated using a hot-wire) as etching agent was essential to prevent parasitic carbon/silicon deposition on the surface
of PAA or on the wall of pores and to improve CNTs/NWs growth. Such organized CNTs/SiNWs arrays are very
promising as advanced microelectronic devices and their potentiality for photosensing applications were investigated.
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.
Since it was isolated in 2004, graphene, the first known 2D crystal, is the object of a growing interest, due to the range of its possible applications as well as its intrinsic properties. From large scale electronics and photovoltaics to spintronics and fundamental quantum phenomena, graphene films have attracted a large community of researchers. But bringing graphene to industrial applications will require a reliable, low cost and easily scalable synthesis process. In this paper we present a new growth process based on plasma enhanced chemical vapor deposition. Furthermore, we show that, when the substrate is an oxidized silicon wafer covered by a nickel thin film, graphene is formed not only on top of the nickel film, but also at the interface with the supporting SiO2 layer. The films grown using this method were characterized using classical methods (Raman spectroscopy, AFM, SEM) and their conductivity is found to be close to those reported by others.
Seung Jin Chae, Fethullah Günes, Ki Kang Kim, Eun Sung Kim, Gang Hee Han, Soo Min Kim, Hyeon-Jin Shin, Seon-Mi Yoon, Jae-Young Choi, Min Ho Park, Cheol Woong Yang, Didier Pribat, Young Hee Lee
Highly crystalline few-graphene layers were synthesized on poly-nickel, Ni(111) and Ni-deposited substrates by
optimizing the mixing ratio of C2H2/H2 and C2H4/H2 and growth time. The hydrogen effect was investigated to minimize
defects and maintain uniformity of the synthesized few-layer graphenes. Using the optimized ratio of hydrogen and
acetylene mixture, few graphene layers with large sizes of up to 4 inches in diameter were also synthesized on Ni
evaporated Si substrate with different thicknesses and were transferred successfully onto PET film. We also found that
the wrinkles, different from inherent ripples, were formed in the graphene layer independent of the location of the grain
boundary of poly-Ni substrate and growth conditions. This was attributed to the formation of a step terrace followed by
the terrace bunching to result in higher wrinkles due to the thermal mismatch existing between Ni substrate and graphene
layers during thermal quenching. A sheet resistance of 233 Ω/sq was obtained at a transmittance of 65%.
This publication deals with the design of carbon nanotubes (CNT) based nano-electromechanical system (NEMS)
consisting in a variable capacitor working at microwave frequencies. This device is based on an array of moveable CNT
cantilever electrostatically actuated over a ground plane (figure 1 and 2). To design this component, a time-efficient
numerical algorithm for the prediction of CNT electromechanical behavior has been developed. This numerical tool
permits to calculate the pull-in voltage and flexion of the CNT's tip for various devices' parameters like CNT's diameter
and length, initial air gap (g) ... Our software also takes into account the Van der Waals (VdW) forces and the fringing
field effects. The results demonstrate that, unlike for RF-MEMS, fringing field effects are preponderant for CNT-based
NEMS.
This paper also discusses on the accuracy of the developed software. In order to validate our prediction, we used
finite element simulation software : COMSOL® and experimental results found in literature and compare them to our
prediction. Results prove that we obtain, for a decrease of the simulation time by two orders of magnitude, a maximum
error on the pull-in voltage of 7% for various kinds of structures and dimensions.
These results were finally used for the design of NEMS demonstrators. The microwave behavior of the varactors,
over a large range of frequency, is presented. Simulations with 3D finite-element-method electromagnetic software were
performed to optimize the structure and predict its microwave performances, which conclude the design of our
microwave carbon nanotubes (CNT) based nano-electromechanical system (NEMS) variable capacitor.
This paper deals with the development of a micro-interconnection technology suitable for the elaboration of RF-NEMS
(Nano-ElectroMechanical Systems) varactors. It aims to present an extension of RF MEMS concept into nano-scale domain
by using multi-walled carbon nanotubes (MWCNT) as movable part instead of micrometric membranes into reconfigurable
passive circuits for microwave applications.
For such a study, horizontal configuration of the NEMS varactors has been chosen and is commented. The technology is
established to fulfill several constraints, technological and microwave ones.
As far as technological requirements are concerned, specific attentions and tests have been carried out to satisfy:
• Possible and later industrialization. No e-beam technique has been selected for RF NEMS varactor elaboration.
Lateral MWCNT growth performed on a Ni catalyst layer, sandwiched between two SiO2 layers, showed
feasibility of suspended MWCNT beam.
• High thermal budget, induced by the MWCNT growth by CVD (Chemical Vapor Deposition), at least to 600°C.
All the dielectric and metallic layers, required to interlink the nano world with the micrometric measurements one,
have been studied accordingly. Consequently, the order of the technological steps has been identified.
About microwave and actuation specifications (targeted close to 25V), the minimization of losses and actuation voltage
implies large layer's thicknesses compared to the CNT diameter.
Several specific technological issues are presented in this paper, taking care of both technological and microwave
compatibility to go toward RF NEMS varactor's elaboration.
We present some early results on the controlled growth of carbon nanotubes inside lateral porous
alumina templates. Such lateral templates provide an easy way of organizing nano-objects in the
plane of their supporting substrate, with potential densities of more than 100/μm, thus paving the
way for the realization of dense circuits. Here we discuss the growth conditions inside the lateral
pores of the templates, with the aim of avoiding the parasitic deposition of amorphous carbon. Our
organization method should also apply to other nanostructures such as semiconductor nanowires.
We present here, a novel approach for the membrane-based synthesis, also called template synthesis of arrays of nanomaterials with monodispersed geometrical features. The basic principle is to grow or generate the desired material inside the pores of a nanoporous alumina membrane. The pores of are synthesised parallel to the surface of the substrate by performing the anodic oxidation of an aluminium thin film laterally, i.e. parallel to the surface of the substrate, instead of perpendicular as usually done. We obtain highly regular and ordered pore arrays, with a minimum pore size in the range of ~3 to 4 nm, which to the best of our knowledge is the smallest reported to date for anodic alumina membranes. After anodic oxidation, the pores of the lateral alumina membranes have been electrochemically “filled” with Te nanowires. Such porous alumina structures may allow to control the in-plane organisation of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication.
William Milne, Ken Teo, N. Rupesinghe, L. Gangloff, E. Minoux, J.-P. Schnell, Dominique Dieumegard, F. Peauger, Pierre Legagneux, David Hasko, Gehan Amaratunga, Didier Pribat
Carbon nano-tubes are alternatives to conventional metal/silicon tips for field emission sources. They exhibit extraordinary field emission properties because of their high electrical conductivity, their high aspect ratio "whisker-like" shape for optimum geometrical field enhancement, and remarkable thermal stability. This paper will review the PECVD growth process, and the micro-fabrication techniques needed to produce well defined carbon nano-tube based micro-electron sources for use in a variety of applications.
Although it has been developed for more than a decade, low temperature polysilicon technology is far from being as mature as its amorphous silicon counterpart. This is due to much more complex processes, that are not used at all in related industrial areas, such as the microelectronics industry. In this paper, we first present the major critical process steps of the low temperature polysilicon technology, including laser crystallization and MOS-type oxide deposition. In a second part, we show that if high information content displays are to be fabricated with organic light emitting materials, they will certainly use a polysilicon active matrix, because of the inherent stability of this material.
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.