共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Shuangchen Lu Mingguang Yao Quanjun Li Hang lv Dedi Liu Bo Liu Ran Liu Linhai Jiang Zhen Yao Zhaodong Liu Bo Zou Tian Cui Bingbing Liu 《Journal of Raman spectroscopy : JRS》2013,44(2):176-182
High‐pressure Raman measurements on single‐wall carbon nanotubes (SWNTs) have been carried out in a diamond anvil cell by using two wavelength lasers: 830 and 514.5 nm. Irrespective of using a pressure transmitting medium (PTM) or not, we found that nanotubes undergo similar transformations under pressure. The pressure‐induced changes in Raman signals at around 2 and 5 GPa are attributed to the nanotube cross‐section transitions from circle to ellipse and then to a flattened shape, respectively. Especially with pressure increasing up to 15–17 GPa, we observed that the third transition takes place in both the Raman wavenumber and the linewidth of G‐band. We propose explanations that the interlinked configuration with sp3 bonds forms in the bundles of SWNTs under pressure, which was the cause for the occurrence of those Raman anomalies, similar to the structural‐phase transition of graphite above 14 GPa. Our TEM observations and Raman measurements on the decompressed samples support this transition picture. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
3.
Single-walled carbon nanotubes (SWNTs) encapsulating C70s, so-called C70 peapods, were synthesized in high yield by a vapor-phase doping method. Raman spectra, high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) measurement indicate that the tube diameter is one of the important factors to determine the orientation of C70 molecules inside the SWNTs. SWNTs with different diameters give different alignment of C70 molecules. The lying orientation is favorable over the standing orientation in thin nanotube, i.e. 1.36 nm nanotubes, whereas the standing orientation is favorable in thick nanotubes, i.e. 1.49 and 1.61 nm nanotubes. 相似文献
4.
We present classical molecular dynamics simulations demonstrating that single-wall carbon nanotube (SWNT) bundles collapse under hydrostatic pressure. The collapse pressures obtained as a function of nanotube diameter are in excellent quantitative agreement with new data presented here for small diameter (d approximately 0.8 nm) SWNTs, and the majority of previously published results, although there remain some unreconciled contradictions in the literature. The collapse pressure is found to be independent of the nanotube chirality, and a lower limit on the largest SWNT that remains inflated at atmospheric pressure is established (d>4.16 nm). 相似文献
5.
We study the effect of the hydrostatic pressure on the phonons in single-walled carbon nanotubes (SWNTs) in a magnetic field. We calculate the magnetic moments of the phonons using a functional integral technique, and find that the phonons in SWNTs undergo a pressure-induced phase transition from the paramagnetic phase to the diamagnetic phase under hydrostatic pressure 2 GPa. We explain the mechanism of generating this phase transition. 相似文献
6.
Ya. Yu. Volkova P. S. Zelenovskiy D. N. Sokolovskiy A. N. Babushkin 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(4):285-287
Single-wall carbon nanotubes (SWNTs) under high pressure exhibit high structural stability and a series of structural transitions up to 35 GPa. As theoretically predicted, the irreversible transformation of SWNTs in the pressure range of 10–30 GPa can be attributed to the polymerization of nanotubes. The electrical conductivity of SWNTs is studied at high pressures up to 35 GPa using a diamond anvil cell (DAC) with electrically conductive anvils of the “rounded cone-plane” type made of synthetic carbonado-type diamonds. SWNTs are studied before and after the application of high pressure using the Raman confocal microscopy technique. Analysis of Raman spectra and pressure dependences of the SWNT resistance shows that the observed structural changes in SWNTs are reversible and no polymerization or collapse are observed. 相似文献
7.
《Physics Reports》2005,409(2):47-99
The use of Raman spectroscopy to reveal the remarkable structure and the unusual electronic and phonon properties of single wall carbon nanotubes (SWNTs) is reviewed comprehensively. The various types of Raman scattering processes relevant to carbon nanotubes are reviewed, and the theoretical foundations for these topics are presented. The most common experimental techniques used to probe carbon nanotubes are summarized, followed by a review of the novel experimental findings for each of the features in the first order and second order Raman spectra for single wall carbon nanotubes. These results are presented and discussed in connection with theoretical considerations. Raman spectra for bundles of SWNTs, for SWNTs surrounded by various common wrapping agents, and for isolated SWNTs at the single nanotube level are reviewed. Some of the current research challenges facing the field are briefly summarized. 相似文献
8.
Single-walled carbon nanotubes (SWNTs) have many interesting properties; they may be metallic or semiconducting depending on their diameter and helicity of the graphene sheet. Hydrostatic or quasi-hydrostatic high pressures can probe many electronic features. Resistance-temperature measurements in SWNTs from normal condition and under 0.4 GPa of quasi-hydrostatic pressures reveal a semiconducting-like behavior. From 0.5 to about 2.0 GPa, the resistance changes to a Kondo-like feature due to magnetic impurities used to catalyse the nanotube formation. Above 2.0 GPa, they become metallic and at about 2.4 GPa, the resistance decreases dramatically around 3 K suggesting a superconducting transition. 相似文献
9.
Yanli Zhao Toshiki Sugai Yahachi Saito 《Journal of Physics and Chemistry of Solids》2007,68(2):284-289
Single-walled carbon nanotubes (SWNTs) were prepared with ethanol chemical vapor deposition (CVD) on SiO2 flat and pillar-patterned Si substrates. The effect of CVD temperatures from 600 to 800 °C on SWNTs yields was investigated. By virtue of its unperturbed environment, an individual suspended SWNT grown between two different SiO2 pillars provides a possibility to study the phonon band structure of SWNT itself at a single-nanotube level. Raman spectra of individual SWNTs grown between pillars were investigated systematically. 相似文献
10.
Single-walled carbon nanotubes (SWNTs) are luminescent. Up to now, two preparation methods, both of which isolate individual SWNTs, have enabled the detection of nanotube bandgap photoluminescence (PL): encapsulation of individual SWNTs into surfactant micelles and direct growth of individual SWNTs suspended in air between pillars. This paper compares the PL obtained from suspended SWNTs to published PL data obtained from encapsulated SWNTs. We find that emission peaks are blueshifted by 28 meV on average for the suspended nanotubes as compared to the encapsulated nanotubes. Similarly, the resonant absorption peaks at the second set of van Hove singularities are blueshifted on average by 16 meV. Both shifts depend weakly on the particular chirality and diameter of the SWNT. PACS 78.67.Ch; 78.55.-m 相似文献
11.
We studied the structural and electronic properties of carbon
nanotubes under hydrostatic pressures based on molecular dynamics
simulations and first principles band structure calculations. It is
found that carbon nanotubes experience a hard-to-soft transition as
external pressure increases. The bulk modulus of soft phase is two
orders of magnitude smaller than that of hard phase. The band
structure calculations show that band gap of (10, 0) nanotube
increases with the increase of pressure at low pressures. Above a
critical pressure (5.70GPa), band gap of (10, 0) nanotube drops
rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge
density shows that a large pressure can induce an
{sp}2-to-{sp}3 bonding transition, which is confirmed by
recent experiments on deformed carbon nanotubes. 相似文献
12.
S. Suzuki N. Asai H. Kataura Y. Achiba 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):143-146
The formation of single-wall carbon nanotubes (SWNTs) by using laser vaporization technique in different ambient gas atmosphere
was investigated. SWNTs were prepared with Rh/Pd (1.2/1.2 atom%)-carbon composite rod in Ar and nitrogen gas atmosphere, respectively.
Raman spectra of raw carbon materials including SWNTs and photoluminescence mapping of dispersed SWNTs in a surfactant solution
demonstrate that the diameter distribution of SWNTs prepared in Ar atmosphere is narrower than those obtained by using CVD
technique (e.g. HiPco nanotube), even when the ambient temperature is as high as 1150 ○C. It was also found that nitrogen atmosphere gives wider diameter distribution of SWNTs than that obtained with Ar atmosphere.
Furthermore, the relative yield of fullerenes (obtained as byproducts) is investigated by using HPLC (high-performance liquid
chromatography) technique. It was found that the relative yield of higher fullerenes becomes lower, when nitrogen is used
as an ambient gas atmosphere. Based on these experimental findings, a plausible formation mechanism of SWNTs is discussed. 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.
A simple and efficient method of chemical functionalization of both single and multiwalled carbon nanotubes has been discussed to give enhanced water solubility by rapidly and efficiently generating an appreciable amount of hydrophilic functional groups using microwave radiation. Surface functionalization containing more than 30 wt% of oxygen has been achieved, resulting into solubility of 2–5 mg/mL. Further covalent functionalization of such soluble SWNTs provides a remarkable degree of aniline functionalization through amidation, where the formation of polyaniline has been avoided. Functionalization of SWNTs is confirmed by techniques like electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, cyclic voltammetry and impedance spectroscopy. Electrochemical analysis suggests an enhanced double layer capacitance (110 F/g) of nanotubes after microwave treatment. Aniline functionalization of SWNTs shows possible variations on the nanotube topography with concomitant formation of a dynamic polymer layer on the nanotube surface. 相似文献
15.
X. B. Dai H. Merlitz C. X. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):109-112
A discrete shell model is proposed to describe the radial
deformation of carbon nanotubes under a hydrostatic pressure and the
radial Young's modulus of (single- or multi-walled) nanotubes is
obtained. It is found that the radial modulus decreases with
increasing tube diameter while increases with increasing number of
layers. The computational results agree well with the previous
results of SWNTs and indicate that the radial modulus of carbon
nanotubes is independent of the Poisson's ratio. 相似文献
16.
E.G. Gamaly A.V. Rode W.K. Maser E. Muñoz A.M. Benito M.T. Martínez G.F. de la Fuente 《Applied Physics A: Materials Science & Processing》2000,70(2):161-168
It has been proved [1] that the use of a CO2-laser system operating in continuous wave mode (cw) can be efficiently used for the production of carbon single-walled nanotubes (SWNTs). In this article we first describe in detail the variable experimental conditions (different ambient gases, static gas pressure, and gas flow) for SWNT formation and summarize the results of the characterization studies of the synthesized materials. Second, we analyze the influence of the different experimental conditions on the SWNTs formation process. We show that the heat transport, kinetic, and diffusion processes allow us to explain seemingly different formation conditions in a qualitative and semi-quantitative agreement with the experimental results. The presented self-consistent scenario for nanotube formation in a gas phase allowed us to propose future experiments on testing the mechanism of nanotube formation. 相似文献
17.
Tang J Qin LC Sasaki T Yudasaka M Matsushita A Iijima S 《Physical review letters》2000,85(9):1887-1889
Single-walled carbon nanotubes show linear elasticity under hydrostatic pressure up to 1.5 GPa at room temperature. The volume compressibility, measured by in situ synchrotron x-ray diffraction, has been determined to be 0.024 GPa (-1). Theoretical calculations suggest that single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the intertubular gap is smaller than the equilibrium spacing of graphite (002) (d = 3.35 A). It has also been determined that the deformation of the trigonal nanotube lattice under hydrostatic pressure is reversible up to 4 GPa, beyond which the nanotube lattice is destroyed. 相似文献
18.
Chemical oxidation of multiwalled carbon nanotubes (MWCNTs) using H2SO4/HNO3 solution has been monitored by micro-Raman spectroscopy and X-ray absorption spectroscopy. The diameter distribution variation in MWCNTs due to chemical oxidation has been measured by scanning electron microscopy and transmission electron microscopy. The Raman dispersion behaviors of the intensity ratio and the band positions of the D, G, and G′ bands were found to be correlated with the MWCNT diameter distribution. It was also found that, during the nanotube unzipping process, defect formation complicates the observation of the diameter-dependent Raman dispersion effect. The curvature effect plays an important role in the intensity ratio trend. On the other hand, defect formation dominates the band position trend. 相似文献
19.
G. V. Pavan Kumar 《Journal of Raman spectroscopy : JRS》2009,40(12):2069-2073
Surface‐enhanced Raman scattering from carbon nanotube bundles adsorbed with plasmon‐tunable Ag‐core Au‐shell nanoparticles (Ag@Au nps) was carried out for the first time. By utilizing nanoparticles whose plasmon resonance peak (541, 642 nm) closely matches the commonly used Raman excitation sources (532, 632.81 nm), we can observe a large enhancement in the Raman signatures of carbon nanotubes. We obtain greater enhancement in the Raman signal for the above case when compared to nanotubes adsorbed with conventional Ag, Au or other ‘off resonant’ Ag@Au nps. The power‐dependent SERS experiment on single‐walled nanotubes (SWNTs) with resonant Ag@Au nps reveals a linear behavior between the G‐band intensity and the photon flux density, which is in agreement with the vibrational pumping model of SERS. The observed enhancement by resonance matching is pronounced for carbon nanotubes and may lead to insights into understanding nanotube–nanoparticle interaction. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
20.
The channels of single-walled carbon nanotubes (SWNTs) are filled with metallic silver. The synthesized nanocomposites are studied by Raman spectroscopy and optical absorption spectroscopy, and these data indicate a substantial modification of the electronic structure of the nanotubes upon their filling. Moreover, X-ray photoelectron spectroscopy shows that the incorporation of the metal leads to a change in the work function of SWNTs due to the Fermi level upshift and to the transfer of an electron density from inserted nanoparticles to the nanotube walls. Thus, the filling of the channels with silver results in donor doping of the nanotubes. 相似文献