摘要:

Conductance of carbon nanotubes (CN's) with a lattice vacancy or strong and short-range impurity potential is studied within a tight-binding model. The conductance is quantized into zero, one, or two times the conductance quantume2/πħ depending on the type of the vacancy if its size is much smaller than the circumference of CN.

ISSN:1058-725X    

DOI:10.1080/10587250008025553

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Electronic states in junctions of nanotubes with different circumferences are studied in an effective-mass approximation. The junction is characterized by boundary conditions which mix wave functions associated with K and K′ points. At ε=0, they decay linearly with the distance from the thicker nanotube, showing that the conductance decays with the junction length in proportion to its third power.

ISSN:1058-725X    

DOI:10.1080/10587250008025554

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The phonon-mediated resistivity is calculated for metallic carbon nanotubes based on a continuum model for electrons and phonons. In armchair nanotubes, only twisting modes contribute to the resistivity, while both stretching and breathing modes are important in zigzag nanotubes. The resistivity shows chirality dependence at low temperatures where breathing modes are not populated but becomes independent of the chirality at high temperatures.

ISSN:1058-725X    

DOI:10.1080/10587250008025555

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

X-ray diffraction profiles of pristine and hypothetical “intercalated” crystalline bundles of single-wall carbon nanotubes are computed and compared with experiment. The pristine case is complicated by finite size effects, tube diameter dispersion and the cylindrical form factor for uncorrelated tube rotations. Experimental profiles of “doped” samples are not in agreement with simulations based on 2-D ordered sublattices except at very low doping levels.

ISSN:1058-725X    

DOI:10.1080/10587250008025556

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Reversible insertion of Li into purified single wall carbon nanotubes was achieved electrochemically. Galvanostatic charge-discharge and cyclic voltammetry indicated that there is no well-defined redox potential for Li insertion or removal in the nanotube lattice. The Li reversible capacity was found to be 460 mA.h/g, significantly higher than the theoretical value for graphite.In-situX-ray diffraction revealed an irreversible loss of the 2-D triangular lattice upon doping.In-situresistivity measurements presented a 20-fold decrease in resistance upon doping, reversible upon undoping.

ISSN:1058-725X    

DOI:10.1080/10587250008025557

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

K-doping into the aggregate of single-wall carbon nanohorns (SWNHs) and into the bundle of single-wall carbon nanotubes (SWNTs) are introduced in this study. Electron spin resonance (ESR) of the pristine SWNHs and SWNTs show that the pristine SWNHs are ESR active and the linewidth (ΔH) is susceptive to the partial pressure of O2, while the pristine SWNTs are ESR silent. ΔHof K-doped SWNHs becomes wider by a factor of −2 than that of the pristine one. For K-doped SWNTs, the Dysonian type ESR comes to be observed. Details of the ESR features are discussed.

ISSN:1058-725X    

DOI:10.1080/10587250008025558

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have measured Raman spectra of bromine doped single-walled carbon nanotubes (SWNTs) using various laser lines to clarify the electronic states of the doped SWNT. In the case of evacuated sample after full doping, two breathing mode peaks were observed simultaneously by visible laser excitations. We assigned the higher frequency peak to the doped SWNT bundles, and the other peak to the undoped portions in the sample. Intensity ratio between them decreased with decreasing excitation energy, and in the infrared region, the breathing mode band of the doped bundle was not observed. These results can be explained by a simple rigid band model.

ISSN:1058-725X    

DOI:10.1080/10587250008025559

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We reportin situmeasurements of four-probe de resistance (R) of K-doped purified single wall carbon nanotube (SWNT) “buckypaper” as a function of quasi-hydrostatic pressure. Doped samples show completely different behavior compared to that of pristine nanotubes in the pressure range up to 90 kbar. The characteristic increase in the resistance of pristine buckypaper above 10 kbar, associated with the formation of kinks or/and twists of tubes, is not observed in K-doped samples. This may originate from 1) a substantial change in electronic band structure of donor intercalated nanotubes, 2) completely different transport properties of defect structures, or 3) higher stiffness of doped SWNT's which prevents formation of kinks and twists in this pressure range. On deintercalation, the pristine behavior ofR(P)is restored, establishing the reversibility of potassium vapor-transport doping.

ISSN:1058-725X    

DOI:10.1080/10587250008025560

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Multiwall (MWNT) and single wall (SWNT) carbon nanotubes were intercalated with heavy alkali metals. From the point of view of their composition, alkali 2D superlattice, EPR and13C NMR characteristics, the intercalation compounds of MWNT (1stand2ndstage) are close to their parent GIC. An expansion of the 2D triangular lattice of SWNT bundles was clearly detected, showing that the alkali atoms are intercalated in the free space between the tubes.

ISSN:1058-725X    

DOI:10.1080/10587250008025561

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Interaction between multiwall nanotubes and intercalating agents (K or FeCl3) was studied using seven different nanotube materials. SEM, TEM, X-ray diffraction, Raman spectroscopy and other techniques were employed to study the reaction products. It was found that the reaction way is determined by nanotube structural type and that nanotubes may exhibit three types of reaction behaviour: intershell intercalation: no-reaction; and intercalation-assisted break-up.

ISSN:1058-725X    

DOI:10.1080/10587250008025562

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor