Carbon nanobuds based on carbon nanotube caps: a first-principles study (original) (raw)
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Electronic and magnetic properties of small fullerene carbon nanobuds: A DFT study
Materials Research Express
The electronic and magnetic properties of carbon nanobuds have been investigated using density functional theory. The carbon nanobuds are formed by attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with (5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having binding energies within the range-0.93eV to-4.06eV. The CC bond lengths near the attachment region increase from the original CC bond lengths. The relative stabilities of the nanobuds are closely related to CC bond lengths and bond angles in cycloaddition reaction. Nanobuds formed by bond cycloaddition are energetically most favorable amongst all cycloadditions. The electronic and magnetic properties of nanobuds depend strongly on electronic properties of its building blocks. The attachment of C20 and C40 on CNTs open up the HOMO-LUMO gaps of nanobuds whereas C28 and C36 results in addition of impurity states near the Fermi level. The total magnetic moment of nanobuds vary from 0.28µB to 4.00µB which depend on the nature of bonding between fullerene and CNTs. The results outline the potential of nanobuds as hybrid carbon nanostructures and how their properties can be tuned with the size and type of fullerene attached.
Electronic Transport Properties of Carbon NanoBuds
2009
Fullerene functionalized carbon nanotubes -- NanoBuds -- form a novel class of hybrid carbon materials, which possesses many advantageous properties as compared to the pristine components. Here, we report a theoretical study of the electronic transport properties of these compounds. We use both ab initio techniques and tight-binding calculations to illustrate these materials' transmission properties, and give physical arguments to interpret the numerical results. Specifically, above the Fermi energy we find a strong reduction of electron transmission due to localized states in certain regions of the structure while below the Fermi energy all considered structures exhibit a high-transmission energy band with a geometry dependent width.
2005
Carbon nanotubes (CNTs) were discovered by S. Iijima, 3 who was looking for new carbon structures, in the deposit formed on graphite cathode surfaces during the electric-arc evaporation (or discharge) that is commonly employed to produce fullerene soot. The CNTs, also known as tubular fullerenes, are cylindrical graphene sheets of sp 2 bonded carbon atoms. These nanotubes are concentric graphitic cylinders closed at either end due to the presence of five-membered rings. The CNTs can be multiwalled with a central tube of nanometric diameter surrounded by graphitic layers separated by ~0.34nm [ ]. Unlike the multi-walled carbon nanotubes (MWNTs), in single-walled carbon nanotubes (SWNTs) there is only the tube and no graphitic layers i.e. SWNTs consist of singular graphene cylindrical walls. In 1999, Rode et al., 4,5 prepared a new form of carbon, a low-density cluster assembled carbon nanofoam. Carbon nanofoam has been prepared by a high-repetition-rate, high-power laser ablation of glassy carbon in Ar atmosphere. The nanofoam possesses a fractallike structure consisting of carbon clusters with an average diameter of 6-9 nm randomly interconnected into a web-like foam.The nanofoam is the first form of pure carbon to display ferromagnetism albeit temporary, at room temperature . 6 Ever since, the discovery of CNTs, several ways of preparing them has been explored. The CNTs have been synthesized by various methods e.g. electric arc discharge, laser evaporation and chemical vapor deposition. 7-9 These methods are very useful and are of widespread importance. The CNTs can be inert and can have a high aspect ratio, high tensile strength, low mass density, high heat conductivity, large surface area and versatile electronic behavior including high electron conductivity.
Formation and growth of carbon nanostructures: fullerenes, nanoparticles, nanotubes and cones
Успехи физических наук, 1997
Various formation models for fullerenes and other carbon nanostructures, such as nanoparticles, nanotubes, and nanocones, are reviewed. The fullerene formation models considered include graphite-fragment and cluster assembling, snail and 'fullerene path' models, and carbon cluster annealing. Selection of magic fullerenes and fullerene isomers following carbon cluster annealing and the subsequent absorption and ejection of the microcluster C2 is discussed. Nanoparticle formation mechanisms are analysed and their relation to fullerene formation mechanisms is discussed. Molecular dynamics simulation of possible nanoparticle mechanisms is considered and possible growth nuclei and growth mechanisms for single-and multishell nanotubes and for carbon cones are discussed. Based on the formation mechanisms considered, fabrication techniques for i) large magic fullerenes, ii) nanoparticles with a tens-of-atoms-strong metal nucleus, and iii) crystals of identical single-shell nanotubes are proposed and described.
Doping of zigzag carbon nanotubes through the encapsulation of small fullerenes
2006
In this work we investigated the encapsulation of C 20 and C 30 fullerenes into semiconducting carbon nanotubes to study the possibility of bandgap engineering in such systems. Classical molecular dynamics simulations coupled to tight-binding calculations were used to determine the conformational and electronic properties of carbon nanotube supercells containing up to 12 fullerenes. We have observed that C 20 fullerenes behave similarly to a p-type dopant while C 30 ones work as n-type ones. For larger diameter nanotubes, where fullerene patterns start to differ from the linear arrangements (peapods), the doping features are preserved for both fullerenes, but local disorder plays an important role and significantly alters the electronic structure. The combined incorporation of both fullerene types (hybrid encapsulation) into the same nanotube leads to a behavior similar to that found in electronic junctions in Silicon-based electronic devices. These aspects can be exploited in the design of nanoelectronic devices using semiconducting carbon nanotubes.
Electron-state control of carbon nanotubes by space and encapsulated fullerenes
Physical Review B, 2003
We report total-energy electronic structure calculations that provide energetics of encapsulation of various fullerenes in carbon nanotubes and electronic structures of resulting carbon peapods. We find that the electron states of the peapods depend on the space in the nanotubes and that they reflect electron states of the encapsulated fullerenes. The deep energy position of the lowest unoccupied state of fullerenes as well as hybridization between states of the fullerenes and the nearly free-electron states of the nanotubes causes a multicarrier character in the peapods.
Study of electronic transport mechanism in carbon nanobuds (CNBs) using first-principles approach
In the present work we have investigated the electronic transport properties of fullerene functionalized single wall carbon nanotube (14,0) i.e. the carbon nanobuds (CNBs) with two different configurations using the first-principles density functional-based non-equilibrium Green function (NEGF) method. Our findings show that the localized states developed in the vicinity of bud region cause strong back-scattering and reduce the electron transmission significantly in the entire energy region. The I-V characteristics of the pristine CNT(14,0) show that it is semiconducting in nature with a threshold voltage 0.55 V. Upon fullerene functionalization of CNT (formation of small neck carbon nanobud) the threshold voltage changes to 0.60V. However on functionalization with long neck (6,0), no noticeable change in threshold voltages is observed. It has been further ascertained from I-V characteristic plots that zigzag nanotubes upon nanobud formation do not change their semiconducting nature. CNBs are promising candidates for nano electronics as they can enhance the cold field emission due to their charge distribution profile which extends from tube to the bud region.
Effects of Cs treatment on field emission properties of capped carbon nanotubes
Surface Science, 2007
Within the methodology [M. Khazaei, A.A. Farajian, Y. Kawazoe, Phys. Rev. Lett. 95 (2005) 177602] based on first-principles electronic structure calculations, the effects of Cs treatment on current emissions and emission patterns of capped carbon nanotubes are considered at low deposition densities when the nanotubes are under an electric field 0.2 V/Å. The results show that the current emission from the cap with one adsorbed Cs is 3.4 times larger than the cap without any Cs. It is 9.6 times larger in the cap with two adsorbed Cs atoms. After Cs deposition the emission patterns become asymmetric (current emission from the carbon atoms located at the topmost pentagon ring close to Cs atoms is larger than the other atomic sites). There are very few localized states on Cs atoms. Hence, although the tunneling probability of electron emission from Cs atoms is significant, there is no current from Cs atoms. In addition, the effect of Cs on work function reduction of nanotubes is explained in terms of Cs deposition densities and the surface dipole moments.
Spectral properties of single-walled carbon nanotubes encapsulating fullerenes
Carbon, 2007
Single-walled carbon nanotubes (SWCNTs) with diameter ranged from 1.22 to 1.6 nm filled with C 60 , C 70 and C 60 H 28 molecules (peapods), as well as double-walled carbon nanotubes (DWCNTs) derived from peapods, were studied by HRTEM, UV-vis-NIR and Raman spectroscopy. Suspensions with accurate concentration were used for spectroscopic studies to enable quantitative comparison of different substances. Filling of the SWCNTs with C 70 molecules resulted in a reduced van der Waals interaction between the tubes in a bundle. The DWCNTs have lower intensity of the van Hove bands and weaker photoluminescence. Raman spectra at 633 and 1064 nm excitation wavelengths reveal that RBM frequencies of C 60 and C 70 peapods are equally downshifted compared to empty tubes. It was found that filling of the nanotubes with C 60 and C 70 caused spectral shifts of absorption bands: thin tubes display red shifts, while thick ones show blue shifts. DWCNTs and C 60 H 28 @SWCNTs do not show any shifts. All the results suggest that the filling of nanotubes with fullerenes alters the average diameter of the electron cloud around SWCNT framework; namely, it increases for thin SWCNTs, and decreases for thick ones. Our attempts to structurally assign thick nanotubes using reported extrapolations from data for thin tubes were unsuccessful.
Heteronuclear carbon nanotubes
2005
The physical properties of double-wall carbon nanotubes (DWCNT) with highly 13C enriched inner walls were studied with Raman spectroscopy and nuclear magnetic resonance (NMR). An inhomogeneous broadening of the vibrational modes is explained by the random distribution of 12C and 13C nuclei based on ab-initio calculations. The growth of DWCNTs from natural and 13C enriched fullerene mixtures indicates that carbon does not diffuse freely along the tube axis during the inner tube growth. The high curvature of the small diameter inner tubes manifests in an increased distribution of the NMR chemical shift tensor components.