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Incoming links: Multi-walled carbon nanotube
This is a multi-walled carbon nanotube with a hollow interior and approximately concentric graphitic shells running along its axis. The walls show many resolved (002) fringes: a relatively straight section supports an approximate count of 16 shells, with some uncertainty from contrast and overlapping/terminated fringes. The tube is not a uniform straight cylinder: the inner channel narrows and changes direction, walls kink and curve, and some inner fringes terminate or join a partly closed internal region. The rough outer boundary contains disordered carbon or incomplete outer layers. The high-contrast material below the tube should not simply be counted as additional concentric shells.
Bending, incomplete walls and changes of atomic bonding scatter charge carriers and can mix shells, reducing the mean free path and causing extra resistance or localization. Covalent intershell links can also increase transfer between shells. Nonhexagonal rings or vacancies are plausible atomic causes, but this image does not resolve a unique ring inventory or prove a specific Stone-Wales defect. Different shell chiralities can intrinsically give different metallic or semiconducting behaviour; a (002) image alone does not assign those chiralities.
The resolved graphitic fringes indicate high-resolution phase contrast in a multi-walled carbon nanotube. Interference of transmitted and diffracted electron waves produces lattice fringes; their darkness is controlled by defocus, thickness and the contrast transfer function, so a dark fringe is not an unqualified map of individual carbon atoms. The weakly scattering central channel is lighter than the multilayer walls. Curved, roughly parallel fringes at its sides identify concentric graphitic shells; the dense fringes at the lower edge arise from overlapping graphitic material or another tube, not necessarily the wall count of the central tube.
Using the printed scale bar, the central tube has an outer diameter of roughly – and an inner channel of roughly –, depending on the cross-section selected away from the overlap. Several wall fringes are resolved on each side, with separations of order , consistent with graphitic interlayer spacing. These are approximate image measurements, not a determination of chirality, chemical purity or an exact shell count. The image alone cannot establish those quantities.
The important distinctions are changes of ring topology, missing or added atoms, and changes of local bonding:
- A Stone-Wales defect rotates one carbon-carbon bond by approximately , converting four hexagons into a --- ring arrangement without adding or removing atoms. It changes strain and electronic scattering.
- A carbon nanotube vacancy defect removes an atom. Reconstruction commonly gives a pentagon and a nine-membered ring, with an undercoordinated site; a reconstructed divacancy can give a -- arrangement. Larger vacancies make holes or broken walls.
- An adjacent pentagon-heptagon pair acts as a dislocation in the hexagonal network. It can connect regions with different wrapping indices, producing a bend or an electronic junction. Isolated nonhexagonal rings impose curvature: pentagons favor positive curvature and heptagons negative curvature.
- An interstitial defect, an adsorbed atom, or chemical functionalization can distort the network and locally change bonding toward . These defects can scatter carriers and create chemically reactive sites.
Closed end caps require nonhexagonal rings, typically six pentagons per hemispherical cap; these are part of the cap topology rather than necessarily damage. Kinks, buckling, branches and incomplete closure are larger-scale structural imperfections.
A multi-walled carbon nanotube can contain any of these defects in individual shells, plus interrupted or terminated shells, extra incomplete graphitic layers, irregular interwall spacing, and covalent interwall bridges formed by displaced atoms. Such bridges change intershell coupling and sliding. Different shells having different wrapping indices is normal and is not, by itself, a defect.