共查询到20条相似文献，搜索用时 21 毫秒
1.
Zhou O Fleming RM Murphy DW Chen CH Haddon RC Ramirez AP Glarum SH 《Science (New York, N.Y.)》1994,263(5154):1744-1747
Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC(8)." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite. 相似文献
2.
Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. "Metallic" zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence on tube radius. These observed energy gaps suggest that most "metallic" single-walled nanotubes are not true metals, and they have implications for our understanding of the electronic properties and potential applications of carbon nanotubes. 相似文献
3.
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
4.
Deheer WA Bacsa WS Châtelain A Gerfin T Humphrey-Baker R Forro L Ugarte D 《Science (New York, N.Y.)》1995,268(5212):845-847
Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties. 相似文献
5.
Morris CA Anderson ML Stroud RM Merzbacher CI Rolison DR 《Science (New York, N.Y.)》1999,284(5414):622-624
Low-density nanoscale mesoporous composites may be readily synthesized by adding a colloidal or dispersed solid to an about-to-gel silica sol. The silica sol can "glue" a range of chemically and physically diverse particles into the three-dimensional silica network formed upon gelation. If the composite gel is supercritically dried so as to maintain the high porosity of the wet gel, a composite aerogel is formed in which the nanoscopic surface and bulk properties of each component are retained in the solid composite. The volume fraction of the second solid can be varied above or below a percolation threshold to tune the transport properties of the composite aerogel and thereby design nanoscale materials for chemical, electronic, and optical applications. 相似文献
6.
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
7.
Capillarity and wetting of carbon nanotubes 总被引：1，自引：0，他引：1
The wetting and capillarity of carbon nanotubes were studied in detail here. Nanotubes are not "super-straws," although they can be wet and filled by substances having low surface tension, such as sulfur, selenium, and cesium, with an upper limit to this tension less than 200 millinewtons per meter. This limit implies that typical pure metals will not be drawn into the inner cavity of nanotubes through capillarity, whereas water and organic solvents will. These results have important implications for the further use of carbon nanotubes in experiments on a nanometer scale. 相似文献
8.
TP Rakitzis SA Kandel AJ Alexander ZH Kim RN Zare 《Science (New York, N.Y.)》1998,281(5381):1346-1349
Isolated diatomic molecules of iodine monochloride (ICl) were photodissociated by a beam of linearly polarized light, and the resulting ground-state Cl atom photofragments were detected by a method that is sensitive to the handedness (helicity) of the electronic angular momentum. It was found that this helicity oscillates between "topspin" and "backspin" as a function of the wavelength of the dissociating light. The helicity originates solely from the (de Broglie) matter-wave interference of multiple dissociating pathways of the electronic excited states of ICl. These measurements can be related to the identity and to the detailed shapes of the dissociating pathways, thus demonstrating that it is possible to probe repulsive states by spectroscopic means. 相似文献
9.
Ghosh S Bachilo SM Simonette RA Beckingham KM Weisman RB 《Science (New York, N.Y.)》2010,330(6011):1656-1659
Controlled chemical modifications of single-walled carbon nanotubes (SWCNTs) that tune their useful properties have been sought for multiple applications. We found that beneficial optical changes in SWCNTs resulted from introducing low concentrations of oxygen atoms. Stable covalently oxygen-doped nanotubes were prepared by exposure to ozone and then light. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than displayed by pristine semiconducting SWCNTs. Dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image than pristine SWCNTs because they give stronger near-infrared emission and do not absorb at the shifted emission wavelength. 相似文献
10.
The uncatalyzed edge growth of carbon nanotubes was investigated by first-principles molecular dynamics simulations. At experimental temperatures the open end of single-walled nanotubes closed spontaneously into a graphitic dome, which may explain why these nanotubes do not grow in the absence of transition metal catalysts. On the other hand, chemical bonding between the edges of adjacent coaxial tubes ("lip-lip" interactions) trapped the end of a double-walled nanotube in a metastable energy minimum, thus preventing dome closure. These calculations show that this end geometry exhibits a high degree of chemical activity and easily accommodates incoming carbon fragments, supporting a model of growth by chemisorption from the vapor phase. 相似文献
11.
To find use in electronics, single-walled carbon nanotubes need to be efficiently separated by electronic type and aligned to ensure optimal and reproducible electronic properties. We report the fabrication of single-walled carbon nanotube (SWNT) network field-effect transistors, deposited from solution, possessing controllable topology and an on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs are tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network in which nanotube chirality separation and simultaneous control of density and alignment occur in one step during device fabrication. Micro-Raman experiments corroborate device results as a function of surface chemistry, indicating enrichment of the specific SWNT electronic type absorbed onto the modified dielectric. 相似文献
12.
综述了近年来碳纳米管的振动特性的理论数值方法研究进展,着重介绍了基于经典连续体理论、分子结构力学/原子有限元以及基于原子研究的分子动力学等方法研究单、多壁碳纳米管振动特性的现状。 相似文献
13.
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
14.
Sfeir MY Beetz T Wang F Huang L Huang XM Huang M Hone J O'Brien S Misewich JA Heinz TF Wu L Zhu Y Brus LE 《Science (New York, N.Y.)》2006,312(5773):554-556
We simultaneously determined the physical structure and optical transition energies of individual single-walled carbon nanotubes by combining electron diffraction with Rayleigh scattering spectroscopy. These results test fundamental features of the excited electronic states of carbon nanotubes. We directly verified the systematic changes in transition energies of semiconducting nanotubes as a function of their chirality and observed predicted energy splittings of optical transitions in metallic nanotubes. 相似文献
15.
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
16.
Remskar M Mrzel A Skraba Z Jesih A Ceh M Demsar J Stadelmann P Levy F Mihailovic D 《Science (New York, N.Y.)》2001,292(5516):479-481
We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes. The nanotubes are up to hundreds of micrometers long and display diverse self-assembly properties on different length scales, ranging from twisted bundles to regularly shaped "furry" forms. The bundles, which contain interstitial iodine, can be readily disassembled into individual molybdenum disulfide nanotubes. The synthesis was performed using a novel type of catalyzed transport reaction including C(60) as a growth promoter. 相似文献
17.
Artificial yeast introns that show cold-sensitive splicing have been constructed. These conditional introns can be inserted into a target gene as an "intron cassette" without disrupting the coding information, allowing expression of the gene to be cold sensitive. Insertion of these intron cassettes rendered the yeast URA3 gene cold sensitive in its expression. The advantage of this intron-mediated control system is that any gene can be converted to a controllable gene by simple insertion of an intron. 相似文献
18.
In the processes that are used to produce single-walled nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of nanotubes assemble continuously from arrays of nanotubes, which are intrinsically long. 相似文献
19.
Cognet L Tsyboulski DA Rocha JD Doyle CD Tour JM Weisman RB 《Science (New York, N.Y.)》2007,316(5830):1465-1468
Single-molecule chemical reactions with individual single-walled carbon nanotubes were observed through near-infrared photoluminescence microscopy. The emission intensity within distinct submicrometer segments of single nanotubes changed in discrete steps after exposure to acid, base, or diazonium reactants. The steps were uncorrelated in space and time and reflected the quenching of mobile excitons at localized sites of reversible or irreversible chemical attack. Analysis of step amplitudes revealed an exciton diffusional range of about 90 nanometers, independent of nanotube structure. Each exciton visited about 10,000 atomic sites during its lifetime, providing highly efficient sensing of local chemical and physical perturbations. 相似文献
20.
Zhao L He R Rim KT Schiros T Kim KS Zhou H Gutiérrez C Chockalingam SP Arguello CJ Pálová L Nordlund D Hybertsen MS Reichman DR Heinz TF Kim P Pinczuk A Flynn GW Pasupathy AN 《Science (New York, N.Y.)》2011,333(6045):999-1003
In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy, Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration. 相似文献