Electronic Structure and Localized States at Carbon Nanotube Tips

Carroll, D. L.; Redlich, Ph.; Ajayan, Pulickel M.; Charlier, Jean‐Christophe; Blase, Xavier; Vita, A. De; Car, Roberto

doi:10.1103/physrevlett.78.2811

Cited by 361 publications

(179 citation statements)

References 22 publications

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“…In reality, the constant-potential surface assumed in the classicalconductor calculations needs to be taken at the outer boundary of the carbon atoms 16 , which makes the CNT electrical radius about 0.42 nm, and decreases the classical prediction of γ s to about 2380 for the simple formula and to about 1310 for eq. (20) in Ref. 10.…”

Section: B Theoretical Discussionmentioning

confidence: 99%

“…There is both experimental and theoretical evidence for the existence of localized states at the end of closed CNTs 19,20,21,22 . A possibility is that the differences in local electronic structure are such that it is energetically favourable for electrons to move from the cylindrical CNT wall into a localised state associated with the top pentagonal ring (or into some other state associated with the cap), thus creating a dipole with its negative end outwards and raising the apex band-structure.…”

Section: Intrinsic Barriers a Barrier Shapesmentioning

confidence: 99%

“…Application of the simple height/radius formula for a metal post with a hemispherical cap 10 , of apparently the same dimensions as our closed CNT (length 1 µm and geometrical radius 0.35 nm) estimates the field enhancement factor as around 2860; a better classical estimate, derived from eq. (20) in Ref. 10, is 1550.…”

Section: Introduction a General Backgroundmentioning

confidence: 99%

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The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Peng

et al. 2008

Journal of Applied Physics

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A 1 µm long, field emitting, (5,5) single-walled, carbon nanotube (SWCNT) closed with a fullerene cap, and a similar open nanotube with hydrogen-atom termination, have been simulated using the MNDO (Modified Neglect of Diatomic Overlap) quantum-mechanical method. Both contain about 80 000 atoms. It is found that field penetration and band-bending, and various forms of chemically and electrically induced apex dipole, play roles. Field penetration may help to explain electroluminescence associated with field emitting carbon nanotubes. Charge-density oscillations, induced by the hydrogen adsorption, are also found. Many of the effects can be related to known effects that occur with metallic or semiconductor field emitters; this helps both to explain the effects and to unify our knowledge about field electron emitters. However, it is currently unclear how best to treat correlation-and-exchange effects when defining the CNT emission barrier. A new form of definition for the field enhancement factor (FEF) is used. Predicted FEF values for these SWCNTs are significantly less than values predicted by simple classical formulae. The FEF for the closed SWCNT decreases with applied field; the FEF for the H-terminated open SWCNT is less than the FEF for the closed SWCNT, but increases with applied field. Physical explanations for this behavior are proposed. Curved Fowler-Nordheim plots are predicted. Overall, the predicted field emission performance of the H-terminated open SWCNT is slightly better than that of the closed SWCNT, essentially because a C-H dipole is formed that reduces the height of the tunnelling barrier. In general, the physics of a charged SWCNT seems more complex than hitherto realised.

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Section: B Theoretical Discussionmentioning

confidence: 99%

Section: Intrinsic Barriers a Barrier Shapesmentioning

confidence: 99%

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The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Peng

et al. 2008

Journal of Applied Physics

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“…Electronic states localized near or at the very end of the nanotube influence the current emission profile [5]. The localized states are relatively well documented for various kinds of tube termination [6][7][8][9]. Such localized states can be induced by the extracting electric field, as shown by recent ab-initio calculations [10].…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional calculation of field emission from carbon nanotubes using a transfermatrix methodology

2001

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We present simulations of field emission from carbon nanotubes, using a transfer-matrix methodology. By repeating periodically a basic unit of the nanotubes in the region preceding that containing the extraction field, specific band-structure effects are included in the distribution of incident states, i.e. those entering the field region. The structures considered are the metallic (5,5) and the semiconducting (10,0) single-wall carbon nanotubes. The total-energy distributions of incident states show the gap of the (10,0) and the expected flat region for the (5,5) nanotube. The field-emitted electron energy distributions contain peaks, which are sharper for the (10,0) structure. Except for peaks associated with van Hove singularities in the distribution of incident states or with the Fermi level in the case of a metallic structure, all peaks are shifted to lower energies by the electric field.

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“…Recently local probe techniques such as ® eld emission microscopy (FEM) (de Heer et al 1995, scanning tunnelling microscopy (STM) (Carroll et al 1997, Tans et al 1997, Bachtold et al 1998, Bezryadin et al 1998, Frank et al 1998, and atomic force microscopy (AFM) (Salvetat et al 1999) have given some insight into the intriguing properties of those novel carbon-based materials. Using FEM it was possible to show that the tips of nanotubes are characterized by well localized electron states from which the ® eld emission takes place preferentially (de Heer et al 1995.…”

mentioning

confidence: 99%

Plasmon excitations in carbon nanotubes

Stockli¹

1999

Philosophical Magazine B

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Electron-energy-loss spectroscopy (EELS) in a high-resolution transmission electron microscope can be used to study the excitation of plasmons in nanometre-size particles with high spatial resolution. For isotropic particles of various shapes, models which allow the attribution of the experimental peaks to a certain excitation mechanism and to understand size-or geometry-dependent variations are well established. Recently, locally anisotropic particles such as nested concentric-shell fullerenes and carbon nanotubes have been discovered and have attracted considerable interest. The plasmon losses of these anisotropic particles measured by EELS could contribute to a better understanding of their physical properties, once the theoretical basis for the interpretation is adapted for anisotropic particles. Encouraged by very good qualitative agreement between a model of the plasmons of nested concentricshell fullerenes based on non-relativistic local dielectric response theory with experimental data, we present here a model for the plasmon excitations of multiwall carbon nanotubes based on the same theoretical approach.

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Electronic Structure and Localized States at Carbon Nanotube Tips

Cited by 361 publications

References 22 publications

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Three-dimensional calculation of field emission from carbon nanotubes using a transfermatrix methodology

Plasmon excitations in carbon nanotubes

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