Pristine and functionalized capped carbon nanotubes under electric fields (original) (raw)
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Effect of electric field on the electronic structures of carbon nanotubes
Applied Physics Letters, 2001
We have investigated the electronic structures of a capped single-walled carbon nanotube under the applied electric field using density functional calculations. The capped tube withstands field strengths up to 2 V/Å. When the electric field is applied along the tube axis, charges are transferred from the occupied levels localized at the top pentagon of the cap, and not from the highest occupied level localized at the side pentagon, to the unoccupied levels. We find that the charge densities at the top of the armchair cap show two-or five-lobed patterns depending on the field strength, whereas those of the zigzag cap show a three-lobed pattern. The interpretation for the images of the field emission microscope is also discussed.
Current Applied Physics, 2009
We have investigated the geometrical and electronic structures of open-end single-walled carbon nanotubes (SWNTs) having chemically modified tips, using semi-empirical AM1 and density functional theory methods. The hydroxyl (-OH), carboxyl (-COOH) and amide (-CONH 2 ) functional groups were used to saturate the open-ends of nanotubes. The effects of functional groups were studied by comparison with the pristine tubes, of which the tubular lengths vary from two to ten unit-cells (40 Å ). The results show that the C-C bond lengths of all model tubes are only slightly different, and the behavior of converging bond lengths in COOH-and CONH 2 -SWNTs is very similar to the pristine tube. Tip functionalization alters the frontier orbitals of the pristine tube, but these effects seem to rapidly decrease as the tubule becomes longer. In general, it can be concluded that the geometrical and electronic structures of pristine tubes after tube-end ''full" functionalization will be preserved, hence supporting that more real-world ''partially" functionalized SWNTs can be used in the same way as the pristine version in most application areas.
Tip-functionalized carbon nanotubes under electric fields
Physical Review B, 2003
We investigated the electronic structures of chemically modified carbon nanotube tips under electric fields using density functional calculations. Hydrogen, oxygen, and hydroxyl group-terminated nanotubes have been considered as field emitters or probe tips. In the case of the open-ended tubes, the field emission originates primarily from the dangling-bond states localized at the edge, whereas the pentagonal defects are the main source of the field emission in the capped tubes. The open-ended nanotube with a zigzag edge is an efficient field emitter because of the localized electronic states around the Fermi level and the atomic alignment of carbon-carbon bonds along with external electric fields. Tip functionalization alters the local density of states as well as the chemical selectivity of nanotubes in various ways. The correlations between atomic geometries of chemically functionalized tips and their electronic structures are further discussed. We propose that a hydrogen-terminated tube would be a promising probe tip for selective chemical imaging.
Electronic structure of carbon nanotubes
1998
A study of the electronic structure of carbon nanoparticles has been carried out using the methods of quantum chemistry and X-ray emission spectroscopy. Fragments of (n, 0) tubes with n = 6, ... ,11 and of (5,5)-(10,0) tubes were calculated using PM3 method. The dependence of the electronic structure of the fragment on length and symmetry was investigated. The structure of the frontier orbitals was shown to change regularly depending on the tube chirality. Band structure of (n,O) and (5,5) tubes was studied by the tight-binding method. A comparison of the basic blocks of the molecular orbitals (MOs) of the fragment and bands of (6,0) and (5,5) tubes was carried out. Experimental CKo spectra. for single-wall and multiwall carbon nanotubules were obtained. These spectra agree satisfactorily with the theoretical spectra plotted as the results of cluster calculations. The structure of the valence zone for the central hexagons of the nanotube fragments keeps the basic features in the ser...
The functionalization of (5, 5), (9, 0), and (10, 0) single wall carbon nanotubes by CHn fragments
Chemical Physics Letters, 2007
The binding energies of CH 3 , CH 3 + H, CH 2 , and CH to (5, 5), (9, 0), and (10, 0) carbon nanotubes are determined computationally. The binding energy of a single CH 3 is very small because only one adsorbate-tube bond is formed for the loss of one tube p bond. For CH 3 + H, CH 2 and CH the binding energies are much larger since two adsorbate-tube bonds form for the loss of one tube p bond. For CH 2 and CH, which bond with two different tube atoms, for some orientations a strong bonding with the tube occurs that results in the breaking of a tube CC bond. The calculated IR spectra show that the C-H stretching and H-C-H bending regions offer the possibility of observing these species.
Journal of the Chinese Chemical Society, 2003
We in ves ti gate the struc ture change of semi con duct ing car bon nanotubes un der an ex ter nal elec tric field with den sity func tional the ory. It is shown that the shape of the nanotube re mains cy lin dri c al and the length of the nanotube is also the same, even un der a strong elec tric field. The only change ob served is the di am e ter of the nanotube. It in creases along with the in crease of the ap plied elec tric field.
Journal of Computational Electronics, 2007
The validity of the DFT models implemented by FIREBALL for CNT electronic device modeling is assessed. The effective masses, band gaps, and transmission coefficients of semi-conducting, zigzag, (n, 0) carbon nanotubes (CNTs) resulting from the ab-initio tight-binding density functional theory (DFT) code FIREBALL and the empirical, nearest-neighbor π-bond model are compared for all semiconducting n values 5 ≤ n ≤ 35. The DFT values for the effective masses differ from the π-bond values by ±9% over the range of n values, 17 ≤ n ≤ 29, most important for electronic device applications. Over the range 13 ≤ n ≤ 35, the DFT bandgaps are less than the empirical bandgaps by 20-180 meV depending on the functional and the n value. The π-bond model gives results that differ significantly from the DFT results when the CNT diameter goes below 1 nm due to the large curvature of the CNT. The π-bond model quickly becomes inaccurate away from the bandedges for a (10, 0) CNT, and it is completely inaccurate for n ≤ 8.
Carbon nanotube functionalization with carboxylic derivatives: a DFT study
Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including -COOX (X0H, CH 3 , CH 2 NH 2 , CH 3 Ph, CH 2 NO 2 , and CH 2 CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of −0.23 to −7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is −CH 2 NO 2 >−CH 2 CN>−H>−CH 2 Ph>−CH 3 > −CH 2 NH 2 . The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for −H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of −CH 2 NO 2 and − CH 2 CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.
Density Functional Study of Functionalization of Carbon Nanotubes with Carbenes
Canadian Chemical Transactions, 2014
DFT calculations have been performed on the interactions of carbon nanotubes and carbenes, in order to perform a comparative study of the sidewall functionalization of the two classes of nanotubes, i.e. armchair and zigzag. The systematic investigation of cycloaddition of both zigzag and armchair carbon nanotubes with :CX 2 (where X = H, F, Cl, Br, I) has been undertaken. The models selected for zigzag and armchair CNT are (10,0) and (6,6), respectively, since they have comparative radii (~8 Å). The bond lengths and binding energies of products are analysed in great detail. The band gaps of these non periodic structures are investigated and correlated with the electronic behavior of 'armchair' and 'zigzag' nanotubes. Our results also confirm the previous studies that armchair nanotubes are thermodynamically more stable than zigzag nanotubes. On comparison of armchair carbon nanotubes with zigzag nanotubes, it is found that trends towards carbenic reactivity are the same in both the cases. The dependence of addition of carbenes on the diameter of the carbon nanotubes is also investigated. The models used for nanotubes in this study range from (3,3) to (10,10). Their reactions with :CH 2 have been studied with first principles DFT calculations. An attempt to rationalize the diameter effects is made on the basis of the structures of the nanotubes. It seems that diameter dependence of the reactivity is because of different pyramidalization and π-orbital misalignment angles in different carbon nanotubes. This leads to higher local strain for tubes of smaller diameter that can be partially relaxed by sidewall addition.