共查询到20条相似文献,搜索用时 46 毫秒
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We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and find that the overall spectral properties are described by the critical statistics similar to that known in the Anderson metal-insulator transition. In the energy spectra, there exist three different regimes characterized by Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies that the electron transport in incommensurate multiwalled nanotubes can be either diffusive, ballistic, or intermediate between them, depending on the position of the Fermi energy. 相似文献
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Edris Faizabadi Ali Bagheri 《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):1828-1831
The influence of vacancy percentage on the energy gap of zigzag single-wall carbon nanotube is investigated by the Green's function method in coherent potential approximation. Our probes for various kinds of zigzag single-wall carbon nanotubes show that by increasing vacancy percentage the energy gap is also increased, so for metallic single-wall carbon nanotubes, a metallic to semi-metallic transition is occurred. However, any transition does not appear for semiconductor carbon nanotubes. So by controlling on concentration of vacancies, one can make a semiconductor SWCNT with a predetermined energy gap which is useful in nanoelectronic devices. 相似文献
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We investigate singlet and triplet trion states in semiconducting carbon nanotubes using a one-dimensional model. It is concluded that singlet trion states in bind up to 13.6% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band gap energy. 相似文献
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Cronin SB Yin Y Walsh A Capaz RB Stolyarov A Tangney P Cohen ML Louie SG Swan AK Unlü MS Goldberg BB Tinkham M 《Physical review letters》2006,96(12):127403
Tunable Raman spectroscopy is used to measure the optical transition energies Eii of individual single wall carbon nanotubes. Eii is observed to shift down in energy by as much as 50 meV, from -160 to 300 degrees C, in contrast with previous measurements performed on nanotubes in alternate environments, which show upshifts and downshifts in Eii with temperature. We determine that electron-phonon coupling explains our experimental observations of nanotubes suspended in air, neglecting thermal expansion. In contrast, for nanotubes in surfactant or in bundles, thermal expansion of the nanotubes' environment exerts a nonisotropic pressure on the nanotube that dominates over the effect of electron-phonon coupling. 相似文献
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《Physics letters. A》2019,383(17):2076-2081
We have theoretically investigated the effect of applying longitudinal and transverse electric field on silicon carbide nanotubes with different orientations of Stone Wales defects. We found that each type of Stone Wales defects maintained different formation energy. We have also successfully proved that the orientation of Stone Wales defects in silicon carbide nanotubes response quite differently upon applying external electric field, whereas, two important and interesting phenomena were observed. First, the semiconductor-metal phase transition occurred in silicon carbide nanotubes as well as the three types of Stone Wales defects. However, clear band gap variations were observed in all silicon carbide nanotubes under study. Second, the band gap variations in pristine silicon carbide nanotubes and nanotubes with different orientations of Stone Wales defects have the same trend, even though all silicon carbide nanotubes have clear band gap values under different strengths of the applied external electric field. However, band gap tuning under longitudinal electric field is less significant compared to band gap tuning under the transverse electric field. 相似文献
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Magnetism in transition-metal-doped silicon nanotubes 总被引:1,自引:0,他引:1
Using first-principles density functional calculations, we show that hexagonal metallic silicon nanotubes can be stabilized by doping with 3d transition metal atoms. Finite nanotubes doped with Fe and Mn have high local magnetic moments, whereas Co-doped nanotubes have low values and Ni-doped nanotubes are mostly nonmagnetic. The infinite Si24Fe4 nanotube is found to be ferromagnetic with nearly the same local magnetic moment on each Fe atom as in bulk iron. Mn-doped nanotubes are antiferromagnetic, but a ferrromagnetic state lies only 0.03 eV higher in energy with a gap in the majority spin bands near the Fermi energy. These materials are interesting for silicon-based spintronic devices and other nanoscale magnetic applications. 相似文献
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提出一个根据拉曼基频模及其倍频模的斯托克斯和反斯托克斯拉曼成分的不同共振行为来探测样品与激光共振的系统能级的方法.此方法被应用到不均匀单壁碳纳米管束样品中某一径向呼吸模频率为219波数的金属型碳纳米管.通过分析呼吸模及其倍频模和切向模的共振行为,获得了该碳纳米管的电子跃迁能量,并获得纳米管C-C最近邻重叠积分因子为2.80 eV.此数值可以很好的解释单壁碳纳米管径向呼吸模的共振行为.
关键词:
单壁碳纳米管
呼吸模
共振拉曼散射
电子跃迁能 相似文献
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Wei Song 《International Journal of Theoretical Physics》2009,48(8):2191-2197
Squashed entanglement is a promising entanglement measure that can be generalized to multipartite case, and it has all of
the desirable properties for a good entanglement measure. In this paper we present computable lower bounds to evaluate the
multipartite squashed entanglement. We also derive some inequalities relating the squashed entanglement to other entanglement
measures. 相似文献
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We have carried out electrical conductivity studies on a single-walled carbon nanotubes dispersed lyotropic liquid crystal consisting of 50 wt.% TX-100 in water as a function of magnetic field and temperature. This system exhibits hexagonal and isotropic phases on heating. For all the applied magnetic fields, the temperature dependence of electrical conductivity of the carbon nanotubes dispersed lyotropic liquid crystal system exhibits a discontinuous change at the hexagonal to isotropic transition temperature. We find that the magnetic field dependence of the hexagonal to isotropic transition temperature is similar to that of the viscosity of the system. Using photo images of the sample, we find that the carbon nanotubes in the lyotropic liquid crystal form magnetic field dependent aggregates. We find spherical, rod and hook-like nanotube aggregates for low and high applied magnetic fields respectively. These nanotube aggregates alter the viscosity of our system which in turn alters the transition temperatures. 相似文献
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Araujo PT Doorn SK Kilina S Tretiak S Einarsson E Maruyama S Chacham H Pimenta MA Jorio A 《Physical review letters》2007,98(6):067401
We have studied the optical transition energies of single-wall carbon nanotubes over broad diameter (0.7-2.3 nm) and energy (1.26-2.71 eV) ranges, using their radial breathing mode Raman spectra. We establish the diameter and chiral angle dependence of the poorly studied third and fourth optical transitions in semiconducting tubes. Comparative analysis between the higher lying transitions and the first and second transitions show two different diameter scalings. Quantum mechanical calculations explain the result showing strongly bound excitons in the first and second transitions and a delocalized electron wave function in the third transition. 相似文献
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The electronic properties of boron nanotubes with axial strain are investigated by first principle calculations. The band
gaps of the (3, 3) and (5, 0) boron nanotubes are found to be modified by axial strain significantly. We find that the semiconductor-metal
transition occurs for the (3, 3) boron nanotubes with both compressive and tensile strain. While for the (5, 0) boron nanotubes,
only the tensile strain induces the semiconductor-metal transition. These boron nanotubes have the largest gaps under compressive
strain.
相似文献
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González J 《Physical review letters》2002,88(7):076403
We propose the model of a manifold of one-dimensional interacting electron systems to account for the superconductivity observed in ropes of nanotubes. We rely on the strong suppression of single-particle hopping between neighboring nanotubes in a disordered rope and conclude that the tunneling takes place in pairs of electrons, which are formed within each nanotube due to the existence of large superconducting correlations. Our estimate of the transition temperature is consistent with the values that have been measured experimentally in ropes with about 100 metallic nanotubes. 相似文献
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Manzoni C Gambetta A Menna E Meneghetti M Lanzani G Cerullo G 《Physical review letters》2005,94(20):207401
We study exciton (EX) dynamics in single-walled carbon nanotubes (SWNTs) included in polymethylmethacrylate by two-color pump-probe experiments with unprecedented temporal resolution. In the semiconducting SWNTs, we resolve the intersubband energy relaxation from the EX2 to the EX1 transition and find time constants of about 40 fs. The observation of a photoinduced absorption band strictly correlated to the photobleaching of the EX1 transition supports the excitonic model for primary excitations in SWNTs. We also detect in the time domain coherent oscillations due to the radial breathing modes at approximately 250 cm(-1). 相似文献
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N掺杂TiO_2纳米管阵列的制备与性质研究 总被引:2,自引:2,他引:0
本文采用阳极氧化法制备了孔径为60-80nm,孔壁厚约为20-30nm的高有序度TiO2纳米管。将制备的TiO2纳米管经表面酸化后在浓氨水中浸泡,并于氮气气氛中进行退火处理,以实现TiO2纳米管的N掺杂。利用SEM、XRD、Raman和XPS对样品的形貌与结构进行了研究。结果显示,掺N后不会破坏阳极氧化形成的高有序纳度米管阵列,而且N的引入促进了TiO2纳米管在低温下由锐钛矿相向金红石相的转变。N掺杂样品的XPS中出现了结合能位于399.7 eV的峰,该峰来源于TiO2的间隙氮杂质,显示此方法在TiO2纳米管中实现了有效的N的掺杂。 相似文献
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This Letter deals with triply-periodic (crystalline) solutions in a family of Skyrme systems, namely where the field takes values in the squashed 3-sphere. The family includes the standard Skyrme model (round 3-sphere), and the Skyrme–Faddeev case (maximal squashing). In the round case, the lowest-energy crystal is the well-known cubic lattice of half-skyrmions; but in the squashed case the minimal-energy crystal structures turn out to be different. We describe some of the solutions that arise, including arrays of vortices and multi-sheeted structures. 相似文献
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N. Zibouche A. Kuc T. Heine 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):49
MoS2 and WS2 layered transition-metal dichalcogenides are indirect
band gap semiconductors in their bulk forms. Thinned to a monolayer, they undergo a
transition and become direct band gap materials. Layered structures of that kind can be
folded to form nanotubes. We present here the electronic structure comparison between
bulk, monolayered and tubular forms of transition metal disulfides using first-principle
calculations. Our results show that armchair nanotubes remain indirect gap semiconductors,
similar to the bulk system, while the zigzag nanotubes, like monolayers, are direct gap
materials, what suggests interesting potential applications in optoelectronics. 相似文献
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We find that the optical properties of carbon nanotubes reflect remarkably strong effects of exciton-phonon coupling. Tight-binding calculations show that a significant fraction of the spectral weight of the absorption peak is transferred to a distinct exciton+phonon sideband, which is peaked at around 200 meV above the main absorption peak. This sideband provides a distinctive signature of the excitonic character of the optical transition. The exciton-phonon coupling is reflected in a dynamical structural distortion, which contributes a binding energy of up to 100 meV. The distortion is surprisingly long ranged, and is strongly dependent on chirality. 相似文献