Deformation Of Carbon Nanotubes Research Articles

Mechanical properties, defects and electronic behavior of carbon nanotubes

Using state-of-the-art classical and quantum simulations, we have studied the mechanical and electronic response of carbon nanotubes to external deformations, such as strain and bending. In strained nanotubes the spontaneous formation of double pentagon–heptagon defect pairs is observed. Tubes containing these defects are energetically preferred to uniformly stretched tubes at strains greater than 5%. These defects act as nucleation centers for the formation of dislocations in the originally ideal graphitic network and constitute the onset of further deformations of the carbon nanotube. In particular, plastic or brittle behaviors can occur depending upon the external conditions and tube symmetry. We have also investigated the effects that the presence of addimers has on strained carbon nanotubes. The main result is the formation of a new class of defects that wrap themselves about the circumference of the nanotube. These defects are shown to modify the geometrical structure and to induce the formation of nanotube-based quantum dots. Finally, we computed transport properties for various ideal and mechanically deformed carbon nanotubes. High defect densities are shown to greatly affect transport in individual nanotubes, while small diameter bent armchair nanotubes mantam thier basic electrical properties even in presence of large deformations with no defects involved.

Band-gap modification by radial deformation in carbon nanotubes

Calculations of the electronic structure demonstrate that band gap modification such as opening and closure is easily achieved by radial deformations perpendicular to the tube axis. Deformations open the gap in metallic armchair tubes only if the mirror symmetries are broken, and further distortions greatly enhance the gap due to new bonds formed between facing layers. Similar deformations increase the gap in small-gap zigzag tubes, but gap closure occurs due to enhanced ${\ensuremath{\sigma}}^{*}\ensuremath{-}{\ensuremath{\pi}}^{*}$ hybridization effects. This band gap modification is crucial at metal contacts and has important implication in fabricating a quantum dot or multiple quantum dots.

Electronic transport in extended systems: Application to carbon nanotubes

We present an efficient approach to describe the electronic transport properties of extended systems. The method is based on the surface Green's function matching formalism and combines the iterative calculation of transfer matrices with the Landauer formula for the coherent conductance. The scheme is applicable to any general Hamiltonian that can be described within a localized orbital basis. As illustrative examples, we calculate transport properties for various ideal and mechanically deformed carbon nanotubes using realistic orthogonal and nonorthogonal tight-binding models. In particular, we observe that bent carbon nanotubes maintain their basic electrical properties even in the presence of large mechanical deformations.

Deformation of carbon nanotubes in nanotube–polymer composites

Composites of uniaxially oriented multiwalled carbon nanotubes embedded in polymer matrices were fabricated and investigated by transmission electron microscopy. In strained composite films, buckling was ubiquitously observed in bent nanotubes with large curvatures. By analyses of a large number of bent nanotubes, the onset buckling strain and fracture strain were estimated to be ≈5% and ⩾18%, respectively. The buckling wavelengths are proportional to the dimensions of the nanotubes. Examination of the fracture surface showed adherence of the polymer to the nanotubes.

Deformation of carbon nanotubes by surface van der Waals forces

The strength and effect of surface van der Waals forces on the shape of multiwalled and single-walled carbon nanotubes is investigated using atomic-force microscopy, continuum mechanics, and molecular-mechanics simulations. Our calculations show that depending on the tube diameter and number of shells, the van der Waals interaction between nanotubes and a substrate results in high binding energies, which has also been determined experimentally. Nanotubes on a substrate may consequently experience radial and axial deformations, which significantly modify the idealized geometry of free nanotubes. These findings have implications for electronic transport and the tribological properties of adsorbed nanotubes.

In-situ observed deformation of carbon nanotubes

In-situ observed deformation of carbon nanotubes

INVESTIGATION OF THE DEFORMED CARBON NANOTUBES

In this paper,we present the experimental observation of the deformed carbon nanotubes,using transmission electron microscopy (TEM).The deformations obsorred include both the radial deformation and the axial deformation. A proposed model can explain qualitatively the occurrence of the deformations of the carbon nanotube in a deposit by arc discharge between two proximate electrodes in argon atmosphere.

塑性変形したカーボンナノチューブの微細組織

塑性変形したカーボンナノチューブの微細組織

Role of sp3 defect structures in graphite and carbon nanotubes

THE discovery of fullerenes1,2 and carbon nanotubes3,4 has led to the realization that it should be possible to tailor the properties of graphitic sheets if their geometry can be controlled5–7. In exploring these possibilities, we have found that the folding and tearing of graphitic sheets follow well defined patterns which seem to be governed by the formation of sp3-like line defects in the sp2 graphitic network. Our studies with the atomic force microscope and scanning tunnelling microscope reveal that these folds and tears occur preferentially along the symmetry axes of graphite, and that 'ripples' are observed in the curved portions of the folds. We also see ripples in deformed carbon nanotubes. They lie along the directions for which sp3-like line defects can form most easily to relieve strain. Our ab initio molecular orbital calculations indicate that the ripples stabilize the π-electronic energy in the bent structures with the total energy balance being determined by the amount of nuclear repulsion. These results provide insight into the geometries that graphitic structures will preferentially accommodate, and the properties that might ensue.