Interwall Interactions Research Articles

Structure and stability of GaS, GaTe, and Janus-Ga2STe multi-walled nanotubes. Molecular mechanics simulation

For the first time, the structural and stability properties of multi-walled GaS, GaTe, and Janus Ga 2 STe nanotubes have been simulated using molecular-mechanics calculations. The armchair and zigzag nanotubes with different wall numbers and diameters have been considered. The force field used for GaS, GaTe and Ga 2 STe multi-walled nanotubes is based on the interaction potentials recently developed to describe monolayers of the transition and post-transition metal chalcogenides. The Buckingham potentials have been introduced to model the interlayer and interwall interactions. The results of quantum mechanical calculations for a number of bulk crystals, mono and bilayers, as well as small diameter single-wall nanotubes have been employed to check the validity of the proposed force field. With the help of an adapted force field, large eight-walled nanotubes with an outer diameter of 32 nm were simulated, which at present cannot be studied using the first principles of quantum mechanical methods. Molecular mechanics simulations predict the faceted structure of armchair GaS, GaTe, and Ga 2 STe multi-walled nanotubes with a sufficiently large diameter and a cylindrical structure for all zigzag nanotubes. The Janus nanotubes' stability is superior to that of binary nanotubes and may probably achieve a maximum at certain wall numbers and diameters. • Janus Ga 2 STe multi-walled nanotubes are more stable than GaS, GaTe MWNTs • Formation energy dependence on diameter has a minimum for Janus MWNTs • Ga 2 STe armchair nanotubes with more than six walls acquire a faceted structure • Zigzag Janus Ga 2 STe multi-walled nanotubes have a circular cross-section • Zigzag multi-walled nanotubes are more stable than armchair ones

Tip-Enhanced Raman Spectroscopy of Multiwalled Carbon Nanotubes through D-Band Imaging: Implications for Nanoscale Analysis of Interwall Interactions

The interwall interactions in multi-walled carbon nanotubes (MWNTs), which are associated with the number of walls and may vary even at nanoscale, are important to investigate as they strongly infl...

Influence of interwall interaction in double-walled aluminogermanate nanotubes on mechanical properties

Interwall interactions among most existing double-walled nanotubes are governed by van der Waals force, which has a trivial impact on the mechanical properties of the nanotubes. In this work, we investigated double-walled aluminogermanate nanotubes (AlGeNTs) that include surface hydroxyl groups capable of forming interwall hydrogen bonds or being bridged by covalent bonds. Compared to van der Waals force, interwall hydrogen bonds have a much stronger influence on the mechanical properties of nanotubes. We employed molecular dynamics and nanoscale continuum mechanics to estimate the Young’s modulus and shear modulus of double-walled AlGeNTs, respectively. We compared the effects of interwall interactions in double-walled AlGeNTs and double-walled carbon nanotubes (CNTs). To amplify the influence of interwall interactions on the elastic modulus of double-walled nanotubes, we also created hypothetical nanotube models in which interwall interactions are represented using covalent bonds. A stronger interwall interaction was shown to increase the Young’s modulus of double-walled nanotubes; however, this produced only a marginal improvement in the shear modulus.

Boundary conditions at closed edge of bilayer graphene and energy bands of collapsed nanotubes

Band structure is theoretically studied in partially flattened carbon nanotubes within an effective-mass scheme. Effects of inter-wall interactions are shown to be important in non-chiral nanotubes such as zigzag and armchair and can essentially be neglected in chiral nanotubes except in the close vicinity of non-chiral tubes. In fact, inter-wall interactions significantly modify states depending on relative displacement in the flattened region in non-chiral tubes and can convert semiconducting tubes into metallic and vice versa. They diminish rapidly when the chiral angle deviates from that of the zigzag or armchair tube, although the decay is slower in the vicinity of armchair tubes.

ChemInform Abstract: Double‐Walled Carbon Nanotube Processing

AbstractReview: 247 refs.

Double-walled carbon nanotube processing.

Single-walled carbon nanotubes (SWCNTs) have been the focus of intense research, and the body of literature continues to grow exponentially, despite more than two decades having passed since the first reports. As well as extensive studies of the fundamental properties, this has seen SWCNTs used in a plethora of applications as far ranging as microelectronics, energy storage, solar cells, and sensors, to cancer treatment, drug delivery, and neuronal interfaces. On the other hand, the properties and applications of double-walled carbon nanotubes (DWCNTs) have remained relatively under-explored. This is despite DWCNTs not only sharing many of the same unique characteristics of their single-walled counterparts, but also possessing an additional suite of potentially advantageous properties arising due to the presence of the second wall and the often complex inter-wall interactions that arise. For example, it is envisaged that the outer wall can be selectively functionalized whilst still leaving the inner wall in its pristine state and available for signal transduction. A similar situation arises in DWCNT field effect transistors (FETs), where the outer wall can provide a convenient degree of chemical shielding of the inner wall from the external environment, allowing the excellent transconductance properties of the pristine nanotubes to be more fully exploited. Additionally, DWCNTs should also offer unique opportunities to further the fundamental understanding of the inter-wall interactions within and between carbon nanotubes. However, the realization of these goals has so far been limited by the same challenge experienced by the SWCNT field until recent years, namely, the inherent heterogeneity of raw, as-produced DWCNT material. As such, there is now an emerging field of research regarding DWCNT processing that focuses on the preparation of material of defined length, diameter and electronic type, and which is rapidly building upon the experience gained by the broader SWCNT community. This review describes the background of the field, summarizing some relevant theory and the available synthesis and purification routes; then provides a thorough synopsis of the current state-of-the-art in DWCNT sorting methodologies, outlines contemporary challenges in the field, and discusses the outlook for various potential applications of the resulting material.

Effective-mass theory of collapsed carbon nanotubes

Band structure is theoretically studied in partially flattened carbon nanotubes within an effective-mass scheme. Effects of interwall interactions are shown to be important in nonchiral nanotubes such as zigzag and armchair and can essentially be neglected in chiral nanotubes except in the close vicinity of nonchiral tubes. In fact, interwall interactions significantly modify states depending on relative displacement in the flattened region in nonchiral tubes and can convert semiconducting tubes into metallic and vice versa. They diminish rapidly when the chiral angle deviates from that of the zigzag or armchair tube, although the decay is slower in the vicinity of armchair tubes.

Molecular dynamics simulations of heat conduction in multi-walled carbon nanotubes

Heat conduction in multi-walled carbon nanotubes (MWNTs) was studied using non-equilibrium molecular dynamics simulations. This research focuses on the effects of the multi-wall structure of the MWNTs on the heat conduction. The results show that the thermal conductivity of a MWNT is almost the same as that of the corresponding single-walled carbon nanotubes (SWNTs) rather than much smaller as has been suggested. Thus, the multi-wall structure does not significantly affect the thermal conduction in the MWNTs. Analysis of the temperature profiles and the phonon density of states confirms that there is almost no heat transport between the MWNT layers and that each layer conducts heat nearly independently along parallel channels. This is physically reasonable since the weak inter-wall interactions and large interfacial thermal resistances make the MWNT layers behave like parallel thermal circuits.

The effect of a transverse electric field on the electronic properties of an armchair carbon nanoscroll

In this work, we use the tight-binding model to study the low-energy electronic properties of carbon nanoscrolls subject to the influences of a transverse electric field. A carbon nanoscroll can be considered as an open-ended spirally wrapped graphene nanoribbon. The inter-wall interactions will alter the subband curvature, create additional band-edge states, modify the subband spacing or energy gap, and separate the partial flat bands. Furthermore, the energy band symmetry about the Fermi level is lifted by such interactions. The truncated Archimedean spiral ρ = r a θ +r is used to describe the spiral structures of carbon nanoscrolls. The energy gap is found to oscillate significantly with r, and exhibits complete energy gap modulations. With the inclusion of a transverse electric field, the band structures are further altered. Inter-wall hoppings will cause electron transfers between different atoms leading to distortions of the electron wavefunctions. The main features of the energy dispersions are directly reflected in the density of states. The numbers, heights, and energies of the density of states peaks are dependent on the electric field strength.

Optical excitations in carbon nanoscrolls

The optical properties of carbon nanoscrolls in the presence of uniform electric fields are investigated by using gradient approximation. Absorption spectra exhibit rich prominent peaks structures, which is caused by one-dimensional sub-bands. The numbers, spectral intensities, and energies of the absorption peaks are strongly dependent on the geometry and the electric field strength. There exists an optical selection rule originating from the two equivalent sublattices in graphene. The two-fold degeneracy of the absorption peaks can be lifted by the inter-wall interactions or the electric field. The variations of the absorption peak energies with the geometry and field strength are also explored. These theoretical predictions can be validated by optical absorption measurements.

Effects of inter wall hopping on the electronic properties of double-wall carbon nanotubes

We study effects of changing inter wall hopping on the electronic and structural properties of ( n , n ) @ ( 2 n , 2 n ) and ( n , 0 ) @ ( 2 n , 0 ) double-wall carbon nanotubes using tight-binding model. We found by switching inter-wall interactions a valley opened in the ( n , n ) @ ( 2 n , 2 n ) local density of states, although both walls remained metallic. For the case of ( n , 0 ) @ ( 2 n , 0 ) where n is not multiple of 3 a semiconducting to metallic phase transition is found, while when n is multiple of 3 both inner and outer walls remained metallic.

Processing and properties of highly enriched double-wall carbon nanotubes

Carbon nanotubes consist of one or more concentric graphene cylinders and are under investigation for a variety of applications that make use of their excellent thermal, mechanical, electronic and optical properties. Double-wall nanotubes are ideal systems for studying the interwall interactions influencing the properties of nanotubes with two or more walls. However, current techniques to synthesize double-wall nanotubes produce unwanted single- and multiwall nanotubes. Here, we show how density gradient ultracentrifugation can be used to separate double-wall nanotubes from mixtures of single- and multiwall nanotubes through differences in their buoyant density. This technique results in samples that are highly enriched in either single- or double-wall nanotubes of similar outer wall diameter, with the double-wall nanotubes being, on average, approximately 44% longer than the single-wall nanotubes. The longer average length of the double-wall nanotubes provides distinct advantages when they are used in transparent conductors.

Molecular dynamics simulations of carbon nanotube oscillators deformed by encapsulated copper nanowires

Pure carbon nanotube (CNT) oscillators are compared to the corresponding CNT oscillators encapsulating copper nanowires (Cu@CNTs) by molecular dynamics simulations. The classical oscillation theory provides a fairly good estimate of the mass dependence of the operating frequency when the CNT surface is not deformed by the Cu nanowire. The structural deformations of the CNT induced by the encapsulated copper nanowire have a greater effect on the oscillation frequency than the mass of the copper nanowire. The excess forces of the Cu@CNT oscillator are slightly higher than those of the CNT oscillator and the excess van der Waals forces induced by the inter-wall interactions are 17 times higher than the excess forces induced by the Cu nanowire–CNT interactions.

First-principles study of the electrical conductance of telescopically aligned carbon nanotubes

We perform a comparative study for the quantum transport of telescoping carbon nanotubes, where the (5,5) and (10,10) nanotubes are coaxially aligned, using first-principles local-density-functional and tight-binding calculations. In both calculations, the intertube conductance initially increases as the hybridized length in the contact region increases, and then decreases, exhibiting a maximum conductance. However, the calculated conductances from first principles are generally smaller than those from the single $\ensuremath{\pi}$-orbital tight-binding model. In the first-principles calculations, we obtain the maximum intertube conductance that does not exceed ${G}_{0}\phantom{\rule{0.3em}{0ex}}(=2{e}^{2}∕h)$, while individual tubes have two conducting channels, giving the conductance of $2{G}_{0}$. On the other hand, the single $\ensuremath{\pi}$-orbital tight-binding model gives the maximum conductance close to $2{G}_{0}$, similar to previous calculations. Using a double-wall nanotube, we examine the effect of interwall interactions on conductance and find that the ${\ensuremath{\pi}}^{*}$ states of the inner and outer tubes are strongly coupled in the tight-binding model, allowing for an extra conducting channel, while the ${\ensuremath{\pi}}^{*}$ channel is closed in the first-principles calculations.

Modelling interwall interactions in carbon nanotubes: fundamentals and device applications

Carbon nanotubes are the most commonly used 'building blocks' of modern nanotechnology. Their unique mechanical and electronic properties, stability and functionality show great promise in creating functional devices on the nanometre scale. One of the great challenges in using this scale is the ability of physical manipulation of the components, such as their positioning and assembling. Strong correlation between the structure and mechanical interactions of the walls of carbon nanotubes provides self-regulation of their relative motion. This can be further exploited in low-friction and high-stiffness devices. In this paper, we present a condensed overview of the recent progress in fundamental understanding of nanomechanical and nanoelectromechanical behaviour of carbon nanotubes and their applications in nanodevices.

Theory of quantum transport in carbon nanotubes: Perfect conductance, dynamical conductivity, and inter-wall interaction

A brief review is given on transport properties of carbon nanotubes mainly from a theoretical point of view. The topics include an effective-mass description of electronic states, the absence of backward scattering except for scatterers with a potential range smaller than the lattice constant, the presence of a perfectly conducting channel, and effects of symmetry breaking perturbations. The dynamical conductivity in the presence of a perfect channel and inter-wall interactions in double-wall nanotubes are also discussed.

First-principles approach to the electron transport and applications for devices based on carbon nanotubes and ultrathin oxides

We use a first-principles computational scheme to study the transport properties of devices based on telescoping carbon nanotubes. The transmission function is calculated through the matrix Green's function method using a Gaussian basis set. Varying the overlap region of the two nanotubes, we compare the effect of interwall interactions on the transport characteristics with that obtained from a simple tight-binding model. The leakage current through ultrathin gate oxides is also studied for various Si/SiO 2 interface models, which are manipulated by varying oxide thickness and crystal phase.

Giant magnetoresistance of multiwall carbon nanotubes: Modeling the tube/ferromagnetic-electrode burying contact

We report on the giant magnetoresistance (GMR) of multiwall carbon nanotubes with ultra small diameters. In particular, we consider the effect of the inter-wall interactions and the lead/nanotube coupling. Comparative studies have been performed to show that in the case when all walls are well coupled to the electrodes, the so-called inverse GMR can appear. The tendency towards a negative GMR depends on the inter-wall interaction and on the nanotube le ngth. If, however, the inner nanotubes are out of contact with one of the electrodes, the GMR remains positive even for relatively strong inter-wall interactions regardless of the outer nanotube length. These results shed additional light on recently reported experimental data, where an inverse GMR was found in some multiwall carbon nanotube samples.

Spectral properties of incommensurate double-walled carbon nanotubes

Incommensurate double-walled carbon nanotubes (iDWCNTs) are one of the simplest nanostructures where we can study the role of incommensurability in quantum transport. We investigate the dynamics of electrons via spectral statistics for different interwall interactions in iDWCNTs. The spectral properties of iDWCNTs are described by Poisson, Wigner–Dyson, and semi-Poisson distributions, depending on the energy regime, implying that the transport nature might be ballistic, diffusive, and intermediate between them. The spectral distribution is found to change from Poisson to Wigner–Dyson as the interwall interaction strength increases. We also analyze the characteristics of wave functions for the three different energy regimes, in conjunction with the transport behavior.

Imaging the interlayer interactions of multiwall carbon nanotubes using scanning tunneling microscopy and spectroscopy

Using atomically-resolved scanning tunneling microscopy and spectroscopy, we probe the nature of interwall interactions within multiwall carbon nanotubes at room temperature. We find that, at low bias voltages, the tunnel current depends strongly on the atomic position, introducing visibility differences between adjacent lattice sites. Since all atoms are equally visible in analogous measurements on single-wall nanotubes, we conclude that these modulations are introduced by the interwall interactions and provide unique information about the stacking nature.