Realistic Nanotube Research Articles

Water diffusion in rough carbon nanotubes.

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of deformation at 300 K. We found that the number of hydrogen bonds that water forms depends on nanotube topology, leading to enhancement or suppression of water diffusion. The simulation results reveal that more realistic nanotubes should be considered to understand the confined water diffusion behavior, at least for the narrowest nanotubes, when the interaction between water molecules and carbon atoms is relevant.

Optical Forces on Silver Homogeneous Nanotubes: Study of Shell Plasmonic Interaction

In previous works (Abraham et al., Plasmonics 6(3):435–444 (2011); Abraham Ekeroth and Lester, Plasmonics 7(4):579–587, (2012); Abraham Ekeroth and Lester, Plasmonics 8:1417–1428 (2013)), we performed an exhaustive study about optical properties of metallic realistic nanotubes, hollow or with dielectric cores. Based on rigorous calculations, involving experimental-interpolated dielectric functions, we pointed out the importance of using an adequate size-corrected dielectric function in homogeneous bidimensional metallic shells when their thicknesses are about several nanometers. In this paper, we compute optical forces induced by electromagnetic plane waves on these kind of nanostructures. We focus the study under p polarisation, in order to observe plasmonic-related behaviour. The optical forces are calculated by the Maxwell’s stress tensor without any kind of approximation. We show three examples of mechanical effects on silver thin shells. The characteristics of the electromagnetic interaction in these structures, from the point of view of forces, allow us to comprehend the problem of the plasmonic interaction in the shell in a new way. We show numerically, for the first time, the nature of bonding/antibonding of surface plasmons in nanotubes made of realistic materials, in a way independent of approximations related to scale. The behaviour of the realistic silver shells is compared with the features deduced from the plasmon hybridization model, which are predicted from a quasi-static approximation of electromagnetic response. Our results conceive a full retarded problem and can only contain numerical errors. In addition, we compare rigorous calculations for the optical forces with those ones obtained from the far field approach, when specified for shell geometry.

Delay and crosstalk reliability issues in mixed MWCNT bundle interconnects

Multi-walled carbon nanotube (MWCNT) bundles have potentially provided attractive solution in nanoscale VLSI interconnects. In current fabrication process, it is not trivial to grow a densely packed bundle having MWCNTs with similar number of shells. A realistic nanotube bundle, in fact, is a mixed CNT bundle consisting of MWCNTs of different diameters. This research paper presents an analytical model of mixed CNT bundle wherein MWCNTs having different number of shells are densely packed. Two different types of MWCNT bundles are presented: (1) MB that contains MWCNTs with similar number of shells (i.e., uniform diameters) and (2) MMB wherein MWCNTs having different number of shells (i.e., non-uniform diameters) are mixed. Multi-conductor transmission line theory is used to present an equivalent single-conductor (ESC) model of different MB and MMB configurations. Using the ESC model, performance is analyzed to address the effect of propagation delay, crosstalk and power dissipation that explores the reliability of an interconnect wire. It is observed that using an MMB arrangement, the overall reduction in delay and crosstalk are 15.33% and 29.59%, respectively, compared to the MB for almost similar power dissipation.

Estimation of the physical properties of nanocomposites by finite-element discretization and Monte Carlo simulation

This paper reviews and enhances numerical models for determining thermal, elastic and electrical properties of carbon nanotube-reinforced polymer composites. For the determination of the effective stress-strain curve and thermal conductivity of the composite material, finite-element analysis (FEA), in conjunction with the embedded fibre method (EFM), is used. Variable nanotube geometry, alignment and waviness are taken into account. First, a random morphology of a user-defined volume fraction of nanotubes is generated, and their properties are incorporated into the polymer matrix using the EFM. Next, incremental and iterative FEA approaches are used for the determination of the nonlinear properties of the nanocomposite. For the determination of the electrical properties, a spanning network identification algorithm is used. First, a realistic nanotube morphology is generated from input parameters defined by the user. The spanning network algorithm then determines the connectivity between nanotubes in a representative volume element. Then, interconnected nanotube networks are converted to equivalent resistor circuits. Finally, Kirchhoff's current law is used in conjunction with FEA to solve for the voltages and currents in the system and thus calculate the effective electrical conductivity of the nanocomposite. The model accounts for electrical transport mechanisms such as electron hopping and simultaneously calculates percolation probability, identifies the backbone and determines the effective conductivity. Monte Carlo analysis of 500 random microstructures is performed to capture the stochastic nature of the fibre generation and to derive statistically reliable results. The models are validated by comparison with various experimental datasets reported in the recent literature.

DFT Investigations of Formic Acid Adsorption on Single-Wall TiO2 Nanotubes: Effect of the Surface Curvature

We carried out a theoretical study based on DFT calculations to provide a detailed characterization of the structural, electronic, and adsorption properties of single-walled TiO2 anatase nanotubes. We investigated nanotube models of increasing diameter, formally obtained by rolling a TiO2 anatase monolayer around the [101] and [010] directions, giving rise to (n,0) and (0,m) nanotubes, respectively. We considered finite cluster models for both (n,0) and (m,0) TiO2 nanotubes, with diameters ranging from 5 to 30 A, thus approaching realistic nanotube dimensions. Our results show that (n,0) tubes are lower in energy with respect to (0,m) tubes. For (n,0) tubes with diameters greater than 23 A, the electronic energy and the band gap are almost converged with respect to the diameter length. We then investigated the adsorption of formic acid on the TiO2 nanotube sidewalls, as the simplest model of photosensitizers binding to the TiO2 surface, relevant to dye-sensitized solar cells. Adsorption of formic acid wa...

Realistic calculations of carbon-based disordered systems

Carbon nanotubes rank amongst potential candidates for a new family of nanoscopic devices, in particular for sensing applications. At the same time that defects in carbon nanotubes act as binding sites for foreign species, our current level of control over the fabrication process does not allow one to specifically choose where these binding sites will actually be positioned. In this work we present a theoretical framework for accurately calculating the electronic and transport properties of long disordered carbon nanotubes containing a large number of binding sites randomly distributed along a sample. This method combines the accuracy and functionality of ab initio density functional theory to determine the electronic structure with a recursive Green's functions method. We apply this methodology on the problem of nitrogen-rich carbon nanotubes, first considering different types of defects and then demonstrating how our simulations can help in the field of sensor design by allowing one to compute the transport properties of realistic nanotube devices containing a large number of randomly distributed binding sites.

Modeling the destruction of realistic nanotube emitters: Relative role of charging and temperature

To discriminate between the effect of charge and temperature as the main cause of structural changes in nanotube-based field-electron emitters, we performed molecular dynamics simulations of charged single- and multiwall carbon nanotubes under realistic conditions. Our results indicate that cap-terminated nanotubes disintegrate abruptly under critical emission conditions. Disintegration, involving either desorption of cap fragments or a transformation into carbon chains and graphitic flakes, occurs prior to melting and is accelerated by Coulomb repulsion that destabilizes the charged tip.

Interaction induced dimerization in zigzag single wall carbon nanotubes

We derive a low-energy effective model of metallic zigzag carbon nanotubes at half filling. We show that there are three important features characterizing the low-energy properties of these systems: the long-range Coulomb interaction, umklapp scattering, and an explicit dimerization generated by interactions. The ratio of the dimerization induced gap and the Mott gap induced by the umklapp interactions is dependent on the radius of the nanotube and can drive the system upon increasing dimerization strength from a Haldane spin-liquid phase through a quantum phase transition with $\mathrm{SU}{(2)}_{1}$ quantum symmetry to a dimerized phase. We consider the physical properties of the phases on either side of this transition, which should be relevant for realistic nanotubes.