67 research outputs found
Electrical conductive double-walled carbon nanotubes � Silica glass nanocomposites prepared by the sol�gel process and spark plasma sintering
The electrical conductivity of suspensions in liquid of several kinds of carbon nanotubes (CNTs) is measured. Raw and soft-functionalized double-walled carbon nanotubes (DWCNTs) appear to be the most promising for achieving a low electrical percolation threshold. A 0.35 vol.% DWCNTs�SiO2 nanocomposite is prepared by the sol�gel process and densified by spark plasma sintering. The obtained material presents a fairly good dispersion of DWCNTs and its electrical conductivity (104 S cm1) is six orders of magnitude higher than that previously reported for 1 vol.% multi-walled CNTs�SiO2
Correlation between resistance fluctuations and temperature dependence of conductivity in graphene
The weak temperature dependence of the resistance R(T) of monolayer
graphene1-3 indicates an extraordinarily high intrinsic mobility of the charge
carriers. Important complications are the presence of mobile scattering centres
that strongly modify charge transport, and the presence of strong mesoscopic
conductance fluctuations that, in graphene, persist to relatively high
temperatures4,5. In this Letter, we investigate the surprisingly varied changes
in resistance that we find in graphene flakes as temperature is lowered below
70 K. We propose that these changes in R(T) arise from the temperature
dependence of the scattered electron wave interference that causes the
resistance fluctuations. Using the field effect transistor configuration, we
verify this explanation in detail from measurements of R(T) by tuning to
different gate voltages corresponding to particular features of the resistance
fluctuations. We propose simple expressions that model R(T) at both low and
high charge carrier densities
Transparent, flexible electrodes and sensors based on carbon nanotube thin films
Hem obtingut capes primes de Nanotubs de Carboni d'una
sola paret (CNT) sobre un substrat amb un mètode molt simple,
que poden ser emprades com elèctrodes flexibles i transparents
en dispositius electrònics. Per tal d'obtenir dispositius
reproduïbles amb propietats similars, en particular amb similar
impedància Z(ω), és important relacionar les propietats elèctriques
amb la quantitat de CNTs presents en la capa.
Per això, hem realitzat capes primes de CNTs sobre substrats
flexibles i transparents (PPC, policarbonat de propilè) amb
diferents densitats de CNT. A partir d'un mètode iteratiu matemàtic
i de l'Anàlisi Tèrmogravimètric (TGA) de cada mostra,
hem pogut determinar la quantitat de CNTs presents en cada
mostra. També n'hem fet una estimació a partir de l'espectroscòpia
d'absorció òptica. Hem vist que els dos mètodes donen
resultats coherents. Hem analitzat les diferents mostres mesurant
la impedància elèctrica a diferents frequències, fins 110
MHz. Les capes primes amb poca densitat de CNTs són semiconductores,
en canvi les denses són metàl·liques, i prou conductores
per ser utilitzades com elèctrode de treball en un procés
electroquímic. Podem obtenir així composites CNT-polímer
conductor o CNT-metall, electroquímicament.
Amb l'objectiu de les aplicacions per a sensors, utilitzant les
capes primes de CNT com elèctrode de treball hem obtingut
composites CNT-polímer conductor, depositant-hi electroquímicament
un polímer conductor, polipirrol o polianilina. Hem
analitzat les propietats del dispositiu com a sensor electroquímic,
observant la seva resposta en funció del pH, mesurant el
potencial en circuit obert en funció del pH de la solució, entre 1
i 13. Els resultats mostren una bona sensibilitat, linearitat i estabilitat.
Per això, els dispositius CNT/polipirrol i CNT/polianilina
poden tenir aplicacions com a sensors o biosensors en estat
sòlid, depositats sobre qualsevol superfície de forma arbitrària,
que pot ser transparent i flexible.We obtained thin films of single-walled carbon nanotubes
(CNTs), which may be used as transparent, flexible electrodes
in electronic devices, on a substrate using a very simple method.
In order to construct reproducible devices with similar
properties, in particular with similar impedance Z(ω), it is important
to associate the electrical properties with the number of
CNTs in a network. We prepared thin CNT networks on transparent,
flexible substrates (PPC, polypropylene carbonate) with
different CNT densities. The number of CNTs was estimated
using a mathematical method based on the data obtained from
thermo-gravimetric analysis (TGA). We were able to estimate
the relative number of CNTs using optical absorption spectroscopy.
These two methods are in good agreement. We also
analysed the various samples using electrical impedance
measurements at frequencies of up to 110 MHz. Low-density
networks are semiconductors, whilst high-density networks
behave like metals and are sufficiently good conductors to be
used as working electrodes in electrochemical processes. It is
thus possible to obtain CNT polymer and metal composite
conductors electrochemically.
With sensor applications in mind, we used CNT thin films as
a working electrode to obtain a composite CNT-conducting
polymer. This was performed by electrochemically depositing a
conducting polymer ? polypyrrole or polyaniline ? on the
electrode. The pH dependence of the device was measured by
recording its open circuit potential in various buffer solutions.
This enabled us to analyse the properties of the device as an
electrochemical sensor. The results showed a good sensitivity,
linearity and stability in both cases. Thus, the CNT/polypyrrole
and CNT/polyaniline devices could have applications as solidstate
gas sensors or biosensors when they are deposited on
transparent and flexible surfaces of any shape
Flexible, transparent electrodes using carbon nanotubes
We prepare thin single-walled carbon nanotube networks on a transparent and flexible substrate with different densities, using a very simple spray method. We measure the electric impedance at different frequencies Z(f) in the frequency range of 40 Hz to 20 GHz using two different methods: a two-probe method in the range up to 110 MHz and a coaxial (Corbino) method in the range of 10 MHz to 20 GHz. We measure the optical absorption and electrical conductivity in order to optimize the conditions for obtaining optimum performance films with both high electrical conductivity and transparency. We observe a square resistance of 1 to 8.5 k[greek capital letter omega] for samples showing 65% to 85% optical transmittance, respectively. For some applications, we need flexibility and not transparency: for this purpose, we deposit a thick film of single-walled carbon nanotubes on a flexible silicone substrate by spray method from an aqueous suspension of carbon nanotubes in a surfactant (sodium dodecyl sulphate), thereby obtaining a flexible conducting electrode showing an electrical resistance as low as 200 [greek capital letter omega]/sq. When stretching up to 10% and 20%, the electrical resistance increases slightly, recovering the initial value for small elongations up to 10%. We analyze the stretched and unstretched samples by Raman spectroscopy and observe that the breathing mode on the Raman spectra is highly sensitive to stretching. The high-energy Raman modes do not change, which indicates that no defects are introduced when stretching. Using this method, flexible conducting films that may be transparent are obtained just by employing a very simple spray method and can be deposited on any type or shape of surface.Postprint (published version
Growth and properties of few-layer graphene prepared by chemical vapor deposition
The structure, and electrical, mechanical and optical properties of few-layer
graphene (FLG) synthesized by chemical vapor deposition (CVD) on a Ni coated
substrate were studied. Atomic resolution transmission electron microscope
(TEM) images show highly crystalline single layer parts of the sample changing
to multilayer domains where crystal boundaries are connected by chemical bonds.
This suggests two different growth mechanisms. CVD and carbon segregation
participate in the growth process and are responsible for the different
structural formations found. Measurements of the electrical and mechanical
properties on the centimeter scale provide evidence of a large scale structural
continuity: 1) in the temperature dependence of the electrical conductivity, a
non-zero value near 0 K indicates the metallic character of electronic
transport; 2) the Young's modulus of a pristine polycarbonate film (1.37 GPa)
improves significantly when covered with FLG (1.85 GPa). The latter indicates
an extraordinary Young modulus value of the FLG-coating of TPa orders of
magnitude. Raman and optical spectroscopy support the previous conclusions. The
sample can be used as a flexible and transparent electrode and is suitable for
special membranes to detect and study individual molecules in high resolution
TEM
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