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1.
The photoresponse in the electrical conductivity of a single-walled carbon nanotube (SWNT) film is dramatically enhanced when the nanotube film is suspended in vacuum. We show here that the change in conductivity is bolometric (caused by heating of the SWNT network). Electron-phonon interactions lead to ultrafast relaxation of the photoexcited carriers, and the energy of the incident infrared (IR) radiation is efficiently transferred to the crystal lattice. It is not the presence of photoexcited holes and electrons, but a rise in temperature, that results in a change in resistance; thus, photoconductivity experiments cannot be used to support the band picture over the exciton model of excited states in carbon nanotubes. The photoresponse of suspended SWNT films is sufficiently high that they may function as the sensitive element of an IR bolometric detector. 相似文献
2.
Bachilo SM Strano MS Kittrell C Hauge RH Smalley RE Weisman RB 《Science (New York, N.Y.)》2002,298(5602):2361-2366
Spectrofluorimetric measurements on single-walled carbon nanotubes (SWNTs) isolated in aqueous surfactant suspensions have revealed distinct electronic absorption and emission transitions for more than 30 different semiconducting nanotube species. By combining these fluorimetric results with resonance Raman data, each optical transition has been mapped to a specific (n,m) nanotube structure. Optical spectroscopy can thereby be used to rapidly determine the detailed composition of bulk SWNT samples, providing distributions in both tube diameter and chiral angle. The measured transition frequencies differ substantially from simple theoretical predictions. These deviations may reflect combinations of trigonal warping and excitonic effects. 相似文献
3.
Heller DA Jeng ES Yeung TK Martinez BM Moll AE Gastala JB Strano MS 《Science (New York, N.Y.)》2006,311(5760):508-511
The transition of DNA secondary structure from an analogous B to Z conformation modulates the dielectric environment of the single-walled carbon nanotube (SWNT) around which it is adsorbed. The SWNT band-gap fluorescence undergoes a red shift when an encapsulating 30-nucleotide oligomer is exposed to counter ions that screen the charged backbone. The transition is thermodynamically identical for DNA on and off the nanotube, except that the propagation length of the former is shorter by five-sixths. The magnitude of the energy shift is described by using an effective medium model and the DNA geometry on the nanotube sidewall. We demonstrate the detection of the B-Z change in whole blood, tissue, and from within living mammalian cells. 相似文献
4.
Kong J Franklin NR Zhou C Chapline MG Peng S Cho K Dai H 《Science (New York, N.Y.)》2000,287(5453):622-625
Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO(2) or NH(3), the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated. 相似文献
5.
Modulation doping of a semiconducting single-walled carbon nanotube along its length leads to an intramolecular wire electronic device. The nanotube is doped n-type for half of its length and p-type for the other half. Electrostatic gating can tune the system into p-n junctions, causing it to exhibit rectifying characteristics or negative differential conductance. The system can also be tuned into n-type, exhibiting single-electron charging and negative differential conductance at low temperatures. The low-temperature behavior is manifested by a quantum dot formed by chemical inhomogeneity along the tube. 相似文献
6.
Solution properties of single-walled carbon nanotubes 总被引：3，自引：0，他引：3
J Chen MA Hamon H Hu Y Chen AM Rao PC Eklund RC Haddon 《Science (New York, N.Y.)》1998,282(5386):95-98
Naked metallic and semiconducting single-walled carbon nanotubes (SWNTs) were dissolved in organic solutions by derivatization with thionychloride and octadecylamine. Both ionic (charge transfer) and covalent solution-phase chemistry with concomitant modulation of the SWNT band structure were demonstrated. Solution-phase near-infrared spectroscopy was used to study the effects of chemical modifications on the band gaps of the SWNTs. Reaction of soluble SWNTs with dichlorocarbene led to functionalization of the nanotube walls. 相似文献
7.
Macroscopic fibers and ribbons of oriented carbon nanotubes 总被引：1，自引：0，他引：1
Vigolo B Pénicaud A Coulon C Sauder C Pailler R Journet C Bernier P Poulin P 《Science (New York, N.Y.)》2000,290(5495):1331-1334
A simple method was used to assemble single-walled carbon nanotubes into indefinitely long ribbons and fibers. The processing consists of dispersing the nanotubes in surfactant solutions, recondensing the nanotubes in the flow of a polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. Flow-induced alignment may lead to a preferential orientation of the nanotubes in the mesh that has the form of a ribbon. Unlike classical carbon fibers, the nanotube fibers can be strongly bent without breaking. Their obtained elastic modulus is 10 times higher than the modulus of high-quality bucky paper. 相似文献
8.
Single-walled carbon nanotubes are ideal systems for investigating fundamental properties and applications of one-dimensional electronic systems. The interaction of magnetic impurities with electrons confined in one dimension has been studied by spatially resolving the local electronic density of states of small cobalt clusters on metallic single-walled nanotubes with a low-temperature scanning tunneling microscope. Spectroscopic measurements performed on and near these clusters exhibit a narrow peak near the Fermi level that has been identified as a Kondo resonance. Using the scanning tunneling microscope to fabricate ultrasmall magnetic nanostructures consisting of small cobalt clusters on short nanotube pieces, spectroscopic studies of this quantum box structure exhibited features characteristic of the bulk Kondo resonance, but also new features due to finite size. 相似文献
9.
The electronic properties of single-walled carbon nanotubes are shown here to be extremely sensitive to the chemical environment. Exposure to air or oxygen dramatically influences the nanotubes' electrical resistance, thermoelectric power, and local density of states, as determined by transport measurements and scanning tunneling spectroscopy. These electronic parameters can be reversibly "tuned" by surprisingly small concentrations of adsorbed gases, and an apparently semiconducting nanotube can be converted into an apparent metal through such exposure. These results, although demonstrating that nanotubes could find use as sensitive chemical gas sensors, likewise indicate that many supposedly intrinsic properties measured on as-prepared nanotubes may be severely compromised by extrinsic air exposure effects. 相似文献
10.
Goldsmith BR Coroneus JG Khalap VR Kane AA Weiss GA Collins PG 《Science (New York, N.Y.)》2007,315(5808):77-81
We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species. By controlling the chemistry through electronically controlled electrochemical potentials, we were able to achieve single chemical attachments. We routinely functionalized pristine, defect-free SWNTs at one, two, or more sites and demonstrated three-terminal devices in which a single attachment controls the electronic response. 相似文献
11.
Carbon nanotubes display either metallic or semiconducting properties. Both large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or "ropes" of aligned single-walled nanotubes (SWNTs), are complex composite conductors that incorporate many weakly coupled nanotubes that each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the different shells. By choosing among the shells, we can convert a MWNT into either a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity allows us to generate entire arrays of nanoscale field-effect transistors based solely on the fraction of semiconducting SWNTs. 相似文献
12.
Fukushima T Kosaka A Ishimura Y Yamamoto T Takigawa T Ishii N Aida T 《Science (New York, N.Y.)》2003,300(5628):2072-2074
When mixed with imidazolium ion-based room-temperature ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transition and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the ionic liquids, but they would readily undergo a gel-to-solid transition on absorbent materials. The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness. 相似文献
13.
Single-molecule fluorescence spectroscopy was used to determine the electronic properties of individual single-walled carbon nanotubes. Carbon nanotube structure was determined simultaneously from Raman spectroscopy. Fluorescence spectra from individual nanotubes with identical structures have different emission energies and linewidths that likely arise from defects or the local environment. Unlike most other molecules studied to date, the fluorescence intensity or spectrum from a single nanotube unexpectedly did not fluctuate. 相似文献
14.
Snow ES Perkins FK Houser EJ Badescu SC Reinecke TL 《Science (New York, N.Y.)》2005,307(5717):1942-1945
We show that the capacitance of single-walled carbon nanotubes (SWNTs) is highly sensitive to a broad class of chemical vapors and that this transduction mechanism can form the basis for a fast, low-power sorption-based chemical sensor. In the presence of a dilute chemical vapor, molecular adsorbates are polarized by the fringing electric fields radiating from the surface of a SWNT electrode, which causes an increase in its capacitance. We use this effect to construct a high-performance chemical sensor by thinly coating the SWNTs with chemoselective materials that provide a large, class-specific gain to the capacitance response. Such SWNT chemicapacitors are fast, highly sensitive, and completely reversible. 相似文献
15.
Strano MS Dyke CA Usrey ML Barone PW Allen MJ Shan H Kittrell C Hauge RH Tour JM Smalley RE 《Science (New York, N.Y.)》2003,301(5639):1519-1522
Diazonium reagents functionalize single-walled carbon nanotubes suspended in aqueous solution with high selectivity and enable manipulation according to electronic structure. For example, metallic species are shown to react to the near exclusion of semiconducting nanotubes under controlled conditions. Selectivity is dictated by the availability of electrons near the Fermi level to stabilize a charge-transfer transition state preceding bond formation. The chemistry can be reversed by using a thermal treatment that restores the pristine electronic structure of the nanotube. 相似文献
16.
Sekitani T Noguchi Y Hata K Fukushima T Aida T Someya T 《Science (New York, N.Y.)》2008,321(5895):1468-1472
By using an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, we uniformly dispersed single-walled carbon nanotubes (SWNTs) as chemically stable dopants in a vinylidene fluoride-hexafluoropropylene copolymer matrix to form a composite film. We found that the SWNT content can be increased up to 20 weight percent without reducing the mechanical flexibility or softness of the copolymer. The SWNT composite film was coated with dimethyl-siloxane-based rubber, which exhibited a conductivity of 57 siemens per centimeter and a stretchability of 134%. Further, the elastic conductor was integrated with printed organic transistors to fabricate a rubberlike active matrix with an effective area of 20 by 20 square centimeters. The active matrix sheet can be uniaxially and biaxially stretched by 70% without mechanical or electrical damage. The elastic conductor allows for the construction of electronic integrated circuits, which can be mounted anywhere, including arbitrary curved surfaces and movable parts, such as the joints of a robot's arm. 相似文献
17.
We have built a torsional pendulum based on an individual single-walled carbon nanotube, which is used as a torsional spring and mechanical support for the moving part. The moving part can be rotated by an electric field, resulting in large but fully elastic torsional deformations of the nanotube. As a result of the extremely small restoring force associated with the torsional deformation of a single molecule, unusually large oscillations are excited by the thermal energy of the pendulum. By diffraction analysis, we are able to determine the handedness of the molecule in our device. Mechanical devices with molecular-scale components are potential building blocks for nanoelectromechanical systems and may also serve as sensors or actuators. 相似文献
18.
Meyer RR Sloan J Dunin-Borkowski RE Kirkland AI Novotny MC Bailey SR Hutchison JL Green ML 《Science (New York, N.Y.)》2000,289(5483):1324-1327
The complete crystallography of a one-dimensional crystal of potassium iodide encapsulated within a 1.6-nanometer-diameter single-walled carbon nanotube has been determined with high-resolution transmission electron microscopy. Individual atoms of potassium and iodine within the crystal were identified from a phase image that was reconstructed with a modified focal series restoration approach. The lattice spacings within the crystal are substantially different from those in bulk potassium iodide. This is attributed to the reduced coordination of the surface atoms of the crystal and the close proximity of the van der Waals surface of the confining nanotube. 相似文献
19.
Bockrath M Liang W Bozovic D Hafner JH Lieber CM Tinkham M Park H 《Science (New York, N.Y.)》2001,291(5502):283-285
We report the characterization of defects in individual metallic single-walled carbon nanotubes by transport measurements and scanned gate microscopy. A sizable fraction of metallic nanotubes grown by chemical vapor deposition exhibits strongly gate voltage-dependent resistance at room temperature. Scanned gate measurements reveal that this behavior originates from resonant electron scattering by defects in the nanotube as the Fermi level is varied by the gate voltage. The reflection coefficient at the peak of a scattering resonance was determined to be about 0.5 at room temperature. An intratube quantum dot device formed by two defects is demonstrated by low-temperature transport measurements. 相似文献
20.
Intramolecular junctions in single-walled carbon nanotubes are potentially ideal structures for building robust, molecular-scale electronics but have only been studied theoretically at the atomic level. Scanning tunneling microscopy was used to determine the atomic structure and electronic properties of such junctions in single-walled nanotube samples. Metal-semiconductor junctions are found to exhibit an electronically sharp interface without localized junction states, whereas a more diffuse interface and low-energy states are found in metal-metal junctions. Tight-binding calculations for models based on observed atomic structures show good agreement with spectroscopy and provide insight into the topological defects forming intramolecular junctions. These studies have important implications for applications of present materials and provide a means for assessing efforts designed to tailor intramolecular junctions for nanoelectronics. 相似文献