共查询到20条相似文献,搜索用时 234 毫秒
1.
Y. Zhang Y. Li W. Kim D. Wang H. Dai 《Applied Physics A: Materials Science & Processing》2002,74(3):325-328
Discrete catalytic nanoparticles with diameters in the range of 1–3 nm are obtained by placing controllable numbers of metal
atoms into the cores of apoferritin. With nanoparticles placed on transmission electron microscope (TEM) grids coated with
ultra-thin alumina membranes, isolated single-walled carbon nanotubes are grown by chemical vapor deposition and directly
examined by TEM. The characterizations, carried out at single-tube and single-particle level, obtain clear evidence that the
diameters of the nanotubes are determined by the diameters of catalytic nanoparticles. For the first time, both ends of an
as-grown single-walled nanotube are imaged by TEM, leading to a microscopic picture of the nanotube-growth mechanism.
Received: 19 September 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
2.
We studied the stability, geometrical structures and electronic energy band of hexagonal silicon nanotube (SiNT) confined inside carbon nanotubes based on first-principle calculations. The results show that the encapsulating process of SiNT is exothermic in (9,9) carbon nanotube while endothermic in (8,8) and (7,7) carbon nanotubes. When the SiNT is inserted into (9,9) carbon nanotube, the insertion energy is about 0.09 eV. Energy band of SiNT@(9,9) nanotube is not distorted greatly compared with the superposition of bands of isolated SiNT and (9,9) carbon nanotube. Especially, a parabolic band occurs near the Fermi level of energy band in SiNT@(7,7) nanotube. Such a band could be a nearly free electronic state originating from carbon nanotube. Moreover, we discuss the variation of total energy as the SiNT rotates around its axis inside carbon nanotubes. 相似文献
3.
Vapor-phase intercalation of a single-walled carbon nanotube sample with Cs was carried out and monitored in situ by Raman spectroscopy. Results indicate that the endpoint of the intercalation was limited by small interstitial gaps in the nanotube bundles. These small-diameter gaps are present because of the significant number of small-diameter nanotubes (0.9-1.0 nm, as calculated from Raman radial breathing mode frequencies) present in the sample. It is not possible to determine from our Raman spectra whether the early endpoint is the result of diffusion limitation or the equilibrium energetics at the endpoint, although some diffusion limitation is observed near the beginning of the reaction. A simple geometric model for expansion of the nanotube bundles under intercalation is presented; this model reproduces, reasonably well, measured expansions reported by others and explains both diffusion- and equilibrium-limited mechanisms in terms of the larger lattice expansion required for smaller-diameter nanotubes. Staging of the intercalation process, in analogy with the staged intercalation of graphite intercalation compounds, is not observed. Instead, the transverse mode peaks undergo a gradual decrease in intensity and a gradual charge transfer- and electronic coupling-induced downshift. 相似文献
4.
In this work, development of a voltage dependent resistance model for metallic carbon nanotubes is aimed. Firstly, the resistance of metallic carbon nanotube interconnects are obtained from ab initio simulations and then the voltage dependence of the resistance is modeled through regression. Self-consistent non-equilibrium Green's function formalism combined with density functional theory is used for calculating the voltage dependent resistance of metallic carbon nanotubes. It is shown that voltage dependent resistances of carbon nanotubes can be accurately modeled as a polynomial function which enables rapid integration of carbon nanotube interconnect models into electronic design automation tools. 相似文献
5.
In this work we performed the filling of single-walled carbon nanotube channels with metallic silver and copper by means of two-step synthesis including imbuing with metal nitrate aqueous solution and further annealing. It has been shown that metal insertion into the nanotube cavities results in the Fermi level upshift and the charge transfer from metal to carbon atoms, thus donor doping of single-walled carbon nanotubes takes place. At the same time, encapsulated silver has a larger donor effect on the carbon nanotubes that has been proved by Raman spectroscopy and X-ray photoelectron spectroscopy. 相似文献
6.
Y. Chen M.J. Conway J.D. Fitzgerald 《Applied Physics A: Materials Science & Processing》2003,76(4):633-636
Multi-walled carbon nanotubes with cylindrical and bamboo-type structures are produced in a graphite sample after mechanical
milling at ambient temperature and subsequent thermal annealing up to 1400 °C. The ball milling produces a precursor structure
and the thermal annealing activates the nanotube growth. Different nanotubular structures indicate different formation mechanisms:
multi-wall cylindrical carbon nanotubes are probably formed upon micropores and the bamboo tubes are produced because of the
metal catalysts. A two-dimensional growth governed by surface diffusion is believed to be one important factor for the nanotube
growth. A potential industrial production method is demonstrated with advantages of large production quantity and low cost.
Received: 17 May 2002 / Accepted: 12 September 2002 / Published online: 4 December 2002
RID="*"
ID="*"Corresponding author. Fax: +61-2/6125-8338, E-mail: ying.chen@anu.edu.au 相似文献
7.
J.M. Cao 《Applied Surface Science》2006,253(5):2460-2464
Three-step raising temperature process was employed to fabricate carbon nanotubes by pyrolysis of ferrocene/melamine mixtures on silica and single crystalline silicon wafers respectively. Then the morphologies, structures and compositions of obtained carbon nanotubes are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscope (EDX) and electron energy-loss spectroscopy (EELS). TEM and SEM observation shows that on silica substrate, high-oriented carbon nanotube can grow compactly to form continuous film on both frontal and cross-section surfaces, but on silicon substrate, only can form on cross-section surface. These carbon nanotubes have much irregular cup-like structure, and with outer diameter varying from 25 nm to 35 nm. At the top end of carbon nanotube there is a catalyst particle. EDX analysis reveals that the particle are iron cluster, and EELS spectrum indicates that the nanotube is composed of pure carbon. Finally, the effect of substrate surface roughness on the growth behavior of carbon nanotubes has been discussed. 相似文献
8.
Jong Hyun Bae 《Applied Surface Science》2007,253(9):4150-4155
Surface functionalization of single-walled carbon nanotube was carried out by introducing ylides groups containing anchored phenol structures. The functionalized nanotube is characterized using elemental analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and zeta potential measurements. Elemental and FT-IR analysis reveal the successful functionalization of azomethine ylides. Raman spectroscopic studies corroborates that the surface functionalization does not affect the basic crystal domain size of the nanotubes. Functionalized carbon nanotubes exhibit higher zeta potential values showing its higher dispersant ability in water and acetone solvent in comparison to pure carbon nanotube. 相似文献
9.
Hendrik Ulbricht 《Surface science》2009,603(10-12):1853-1862
We review recent experimental investigations of the interaction of gases with the surface of single-wall carbon nanotube bundles. We discuss thermal desorption spectra of both non-polar and polar adsorbates for low and high coverage. We show experimental results for diffusion processes of Xe along and within carbon nanotube bucky paper material, which is consistent with a recently proposed coupled desorption diffusion (CDD) model. We further discuss details of the interaction of ammonia with carbon nanotube surfaces, including the experimental investigation of the influence of adsorbed ammonia on the electrical transport properties of carbon nanotubes under ultra-high vacuum conditions. 相似文献
10.
A nonlocal Levinson beam model is developed to study the free vibrations of a zigzag single-walled carbon nanotube (SWCNT) in thermal environments. The equivalent Young’s modulus and shear modulus for a zigzag SWCNT are derived using an energy-equivalent model. The present study illustrates that the vibration characteristics of an SWCNT are strongly dependent on the temperature change and on the chirality of a zigzag carbon nanotube. The investigation of the chirality and temperature effects on free vibration of carbon nanotubes may be used as a useful reference for the application and the design of nanoelectronic and nanodrive devices, nano-oscillators, and nanosensors, in which carbon nanotubes act as basic elements. 相似文献
11.
A theoretical model for the growth of single-wall carbon nanotubes produced by metal-catalyzed decomposition of hydrocarbons
and fullerenes is presented. The growth process is treated as a thermodynamic equilibrium between carbon in the gas phase
and carbon in the nanotube. The minimum possible nanotube diameters based on several published experimental conditions are
calculated by combining the free energy of the reaction with an equation derived from elastic theory. The model predicts the
possibility of generating nanotubes with extremely small diameters that are smaller than in the corresponding experiments.
Received: 18 July 2001 / Accepted: 19 November 2001 / Published online: 4 March 2002 相似文献
12.
Gold nanoclusters were directly synthesized on thiol functionalized carbon nanotubes film and characterized by means of X-ray photoelectron spectroscopy. A carbon nanotube (CNT) supporting network was produced by spreading a concentrate suspension of thiol-functionalized CNT on platinum films. To synthesize gold nanoclusters, a water solution of tetrachloroauric acid was adsorbed on the CNT substrate and reduced by UV reduction in air. Detailed analysis of the Au 4f core line enabled us to follow the chemical modifications occurring on the substrate. In particular, the XPS analysis of gold features shows a progressive reduction of the gold precursor by increasing the irradiation time. Also information on the nanocluster size distribution after each reducing treatments are obtained. 相似文献
13.
We reported a simple method to fabricate polymer nanocomposites with single-walled carbon nanotubes (SWNTs) having exceptional alignment and improved mechanical properties. The composite films were fabricated by casting a suspension of single walled carbon nanotubes in a solution of thermoplastic polyurethane and tetrahydrofuran. The orientation as well as dispersion of nanotubes was determined by scanning electron microscopy, transmission electron microscopy and polarized Raman spectroscopy. The macroscopic alignment probably results from solvent-polymer interaction induced orientation of soft segment chain during swelling and moisture curing. The tensile behavior of the aligned nanotube composite film was also studied. At a 0.5 wt.% nanotube loading, a 1.9-fold increase in Young's modulus was achieved. 相似文献
14.
The coefficients of electron diffusion and conductivity have been calculated for single-layer semiconducting carbon nanotubes
in an external electric field with the strength vector directed along the nanotube axis. The evolution of the electronic system
of the nanotubes has been described using the Boltzmann kinetic equation in terms of the quasi-classical approximation of
relaxation time. An analytical expression of the electron diffusion coefficient has been obtained, and its nonlinear field
dependence has been revealed. 相似文献
15.
用原位乳液聚合法在碳纳米管表面包覆聚苯胺,制备出了碳纳米管/聚苯胺一维纳米复合管.复合管的直径为50—80 nm,聚苯胺包覆层的厚度为20—30 nm,聚苯胺在碳纳米管表面以层状和枝晶状两种形态生长.研究了碳纳米管/聚苯胺复合管在2—18 GHz的微波介电特性.与纯碳纳米管相比,碳纳米管/聚苯胺复合管的介电常数的实部ε′和虚部ε″在2—18 GHz随频率变化较小,在低频波段介电常数值较小,作为微波吸收剂容易实现与自由空间的阻抗匹配,而且它的介电损耗角正切(tanδ=ε″/ε′)较高,是一种很好的微波吸收剂.
关键词:
碳纳米管
聚苯胺
微波介电特性
微波吸收剂 相似文献
16.
Intramolecular junctions (IMJs) of carbon nanotubes hold a promise of potential applications in nano-electromechanical systems. However, their structure-property relation is still unclear. Using the revised second-generation Tersoff-Brenner potential, molecular dynamics simulations were performed to study the mechanical properties of single-walled to four-walled carbon nanotubes with IMJs under uniaxial tension. The dependence of deformation and failure behaviors of IMJs on the geometric parameters was examined. It was found that the rupture strength of a junction is close to that of its thinner carbon nanotube segment, and the rupture strain and Young's modulus show a significant dependence on its geometry. The simulations also revealed that the damage and rupture of multi-walled carbon nanotube junctions take place first in the innermost layer and then propagate consecutively to the outer layers. This study is helpful for optimal design and safety evaluation of IMJ-based nanoelectronics. 相似文献
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19.
C.D. Scott S. Arepalli P. Nikolaev R.E. Smalley 《Applied Physics A: Materials Science & Processing》2001,72(5):573-580
Mechanisms proposed in the literature are compared with a current scenario for the formation of single-wall carbon nanotubes
in the laser-ablation process that is based on our spectral emission and laser-induced fluorescence measurements. It is suggested
that the carbon which serves as feedstock for nanotube formation not only comes from the direct ablation of the target, but
also from carbon particles suspended in the reaction zone. Fullerenes formed in the reaction zone may be photo-dissociated
into C2 and other low molecular weight species, and also may serve as feedstock for nanotube growth. Confinement of the nanotubes
in the reaction zone within the laser beam allows the nanotubes to be ‘purified’ and annealed during the formation process
by laser heating.
Received: 2 November 2000 / Accepted: 3 November 2000 / Published online: 23 March 2001 相似文献
20.
Single wall carbon nanotubes with small diameters (〈 5.0 A) subjected to bending deformation are simulated by orthogonal tight-binding molecular dynamics approach. Based on the calculations of C-C bond stretching and breaking in the bending nanotubes, we elucidate the atomistic failure mechanisms of nanotube with small diameters. In the folding zone of bending nanotube, a large elongation of C-C bonds occurs, accounting for the superelastic behaviour. The C-C bonds parallel to the axis direction of nanotube are broken firstly due to the sustained longitudinal stretching strain, giving rising to forming one-notch or two-notch bond-breaking mode depending on nanotube chirMities. The direct bond-breaking mechanism is responsible for the brittle fracture behaviour of nanotubes with small diameters. 相似文献