nanoquebec 2006-12-12 05:01
碳纳米管电性能的测试
最近有人问道单根碳纳米管电学性能的测试问题,觉得有必要介绍和收集这方面的资料,方便大家使用.
[quote]
[b]Researchers at the Naval Research Laboratory, US, have used capacitance changes in a network of single-walled carbon nanotubes to detect the presence of chemical vapours. The technique provides a fast response and is sensitive to a broad range of gases.[/b]
“[color=DarkGreen][b]Direct measurement of the capacitance of an individual single-walled carbon nanotube is difficult because it is so small - approximately 10-16 F[/b][/color],” researcher Eric Snow told nanotechweb.org. “Our devices were fabricated using two-dimensional networks of single-walled carbon nanotubes that contain many thousands of nanotubes. In this way, the capacitance is easily measured.”
Gas molecules adsorb onto the surface of the carbon nanotubes and become polarized by the electric field radiating from the nanotube electrodes. This increases the capacitance of the nanotubes.
To make their device, the scientists deposited a network of nanotubes on a 250 nm-thick thermal oxide layer on a heavily doped silicon substrate. The nanotubes act as one plate of the capacitor while the doped silicon substrate acts as the other. The researchers also created a 2 x 2 mm interdigitated array of palladium electrodes on top of the nanotube layer. These provided electrical contacts.
Applying a 30 kHz, 0.1 V AC voltage between the nanotubes and the substrate, and detecting the out-of-phase AC current with a lock-in amplifier enabled the scientists to measure the capacitance.
Other nanotube gas-detection techniques monitor changes in the resistance of the nanotubes, but these sensors are often troubled by noisy signals and only respond to a limited number of gases.
“The capacitance transduction mechanism eliminates the noise problem, is very sensitive, completely reversible and responds to a broad range of chemical vapours,” said Snow.
The team also coated the nanotubes with chemoselective materials to increase their capacitive response to particular gases. By adding a thin layer of hydrogen-bonding polymer to the tubes, the researchers decreased the minimum detectable level for dimethylmethylphosphonate - a simulant for the nerve agent sarin - to 0.5 ppb. Replacing the polymer with a hydrogen-bonding molecular monolayer gave an improved response time and a minimum detectable level of 50 ppb.
Snow and colleagues say their devices compared favourably with commercially available chemicapacitor sensors, having both higher sensitivity and faster response and recovery times. They believe the faster response times arose because their devices used a much thinner layer of chemoselective material than the commercial ones.
“We are currently working with a company that specializes in single-walled carbon nanotube sensors,” said Snow. “The potential applications include [detecting] chemical warfare agents, toxic industrial chemicals and explosives for defence and homeland security applications. There may also be some medical applications.”
Now Snow says he and his colleagues are improving the design of their sensors, developing chemoselective coatings that are custom-designed for single-walled carbon nanotubes, incorporating their sensors into a compact vapour delivery system, and starting to work on biosensing.
The researchers reported their work in Science.[/quote]
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[size=+3][b]Capacitance and Conductance ofSingle-Walled Carbon Nanotubes in thePresence of Chemical Vapors
[/b]
Eric S. Snow* and F. Keith Perkins
Naval Research Laboratory, Washington, D.C. 20375
[b]Nano Lett., [/b]5 (12), 2414 -2417, 2005. 10.1021/nl051669c S1530-6984(05)01669-3
Abstract:
Simultaneous conductance and capacitance measurements on a single-walled carbon nanotube (SWNT) network are used to extract an intrinsic property of molecular adsorbates. Adsorbates from dilute chemical vapors produce a rapid response in both the capacitance and the conductance of the SWNT network. These responses are caused by a combination of two distinct physiochemical properties of the adsorbates: charge transfer and polarizability. We find that the ratio of the conductance response to the capacitance response is a concentration-independent intrinsic property of a chemical vapor that can assist in its identification.
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[quote]
Capacitance measurements of individual carbon nanotubes
Donev, Luke A. K.; Ilani, Shahal; McEuen, Paul L.
American Physical Society, APS March Meeting, March 13-17, 2006, abstract #U31.005
Publication Date: 03/2006
Origin: APS
Bibliographic Code: 2006APS..MARU31005D
Abstract
We present measurements of the capacitance of individual single walled carbon nanotubes. The nanotubes were grown from ethylene at 700^oC using evaporated iron nanoclusters as the catalyst. Electrical contacts and local top gates were patterned using optical lithography and liftoff. The top gate consists of a thin oxide film (∼15 nm, different oxides have been used) covering the nanotube with metal on top. The capacitance was measured between the nanotube and the top gate using a commercially available capacitance bridge. We also measure the transport through the tube and correlate the transport and capacitance measurements. For semiconducting tubes, we measure the difference in capacitance between the conducting state and the state where the charge carriers in the tube are depleted. The measured capacitance per unit length of the nanotube is in reasonable agreement with the geometric capacitance of a metal wire embedded in oxide near a conducting plane.[/quote]
nanoquebec 2006-12-12 05:04
[b][i]Nature Physics[/i][/b] [b]2[/b], 687 - 691 (2006); doi:10.1038/nphys412
[b]Measurement of the quantum capacitance of interacting electrons in carbon nanotubes[/b]
S. Ilani, L. A. K. Donev, M. Kindermann and P. L. McEuen
Top of page
The electronic capacitance of a one-dimensional system such as a carbon nanotube is a thermodynamic quantity that contains fundamental information about the ground state1. It is composed of an electrostatic component describing the interactions between electrons and their correlations, and a kinetic term given by the electronic density of states. Here, we use a field-effect transistor geometry to obtain the first direct capacitance measurement of individual carbon nanotubes, as a function of the carrier density. Our measurements detect the electrostatic part of the capacitance as well as the quantum corrections arising from the electronic density of states. We identify the van-Hove singularities that correspond to the one-dimensional electron and hole sub-bands and show that the measured capacitance exhibits clear electron–hole symmetry. Finally, our measurements suggest the existence of a negative capacitance, which has recently been predicted to exist in one dimension as a result of interactions between electrons2, 3, 4.
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1. Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, New York 14853, USA
Correspondence to: S. Ilani e-mail: shahal.ilani@cornell.edu
Correspondence to: P. L. McEuen e-mail: mceuen@ccmr.cornell.edu
nanoquebec 2006-12-12 05:12
Static Dielectric Properties of Carbon Nanotubes from First Principles
Kozinsky, Boris; Marzari, Nicola
[b][i]Physical Review Letters,[/i][/b] vol.[b] 96[/b], Issue 16, id. 166801[table=98%][tr][td]
DOI: 10.1103/PhysRevLett.96.166801
[/td][/tr][/table]We characterize the response of isolated single-wall (SWNT) and multiwall (MWNT) carbon nanotubes and nanotube bundles to static electric fields using first-principles calculations and density-functional theory. The longitudinal polarizability of SWNTs scales as the inverse square of the band gap, while in MWNTs and bundles it is given by the sum of the polarizabilities of the constituent tubes. The transverse polarizability of SWNTs is insensitive to band gaps and chiralities and is proportional to the square of the effective radius; in MWNTs, the outer layers dominate the response. The transverse response is intermediate between metallic and insulating, and a simple electrostatic model based on a scale-invariance relation captures accurately the first-principles results. The dielectric response of nonchiral SWNTs in both directions remains linear up to very high values of applied field.
nanoquebec 2006-12-12 05:14
[b]Electrical conductivity and dielectric properties of multiwalled carbon nanotube and alumina composites[/b]
[b][i]Appl. Phys. Lett.[/i][/b] [b]89[/b], 133122 (2006): doi:10.1063/1.2357920
Kaleem Ahmad, Wei Pan, and Sui-Lin Shi
State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, People's Republic of China
(Received 22 June 2006; accepted 17 August 2006; published online 28 September 2006)
Alumina/multiwalled carbon nanotube (MWNT) composites with different MWNT contents ranging from 0.5 to 10 vol % were prepared by spark plasma sintering technique. The dc electrical conductivity and dielectric properties of the composites were investigated and percolation theory was applied to demonstrate the electrical property transition from insulator to conductor. The experimental results have shown that the electrical conductivity increased sharply as the content of MWNTs was close to percolation threshold of 0.79 vol %. In the low frequency range, the dielectric constant reached as high as 5000 when the content of MWNTs was at 1.74 vol % and nearly frequency independent.
lichen92 2008-04-11 06:24
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