Double-walled Nanotubes Research Articles

Understanding the Stability of Finite Double Walled Phenine and its Hybrid Structures using DFT Investigation

Abstract We have performed ab initio calculations based on density functional theory to investigate the structural and electronic properties
of finite double wall phenine nanotubes and their hybrid structures with armchair carbon nanotubes. The result shows that double wall
phenine nanotubes and the hybrid structures are quite stable. The stability of structure is strongly depends on inter-layer separation be-
tween the two tubes. The double walled phenine nanotubes are more stable than their corresponding pristine armchair tubes and exhibit
a semi-conducting nature with a HOMO-LUMO gap of 2.78eV and 2.80eV. The hybrid structures have a small electronic gap between
0.13eV-0.50eV similar to double wall armchair nanotubes. The results highlight the possibility of the synthesis of novel semi-conducting
double wall phenine structures.

Electron-scale origin of structural superlubricity

First-principles computations are performed to study the phenomenon of structural superlubricity (SSL) relative to self-mismatched heterojunctions, rotating-mismatched homojunctions and curvature-mismatched coaxial double-walled nanotubes. It follows from the computations that the interfacial electron density fluctuation is responsible for all characteristics of SSL and can serve as predicting and describing them efficiently. This result further reveals that SSL comes from the fact that the incommensurable contact of two inert surfaces weakens their electronic interactions considerably. The model of SSL based on the electron redistribution a fortiori overcomes the limitations presented by the models of SSL based on the registry index (RI) or on the local pinning (LP).

One-step synthesis of double-walled NiCo2O4 hollow nanotubes using hollow fiber templates created by airflow-coaxial electrospinning

Metal oxide electrode material NiCo2O4 has significant potential for application as an Electrode material due to its excellent electrochemical performance and environmentally friendly characteristics. This paper utilizes a unique airflow-coaxial electrospinning technique combined with a simple one-step solution reaction to prepare NiCo2O4 nanotubes with a complex double-walled hollow structure. The XPS and XRD results demonstrated the synthesis of the NiCo2O4 materials, while the SEM and TEM results verified the presence of a double-walled hollow structure in the NiCo2O4 nanotubes. The electrochemical performance of the NiCo2O4 double-walled hollow nanotubes is significantly improved compared to those single-layer hollow nanotubes. The maximum specific capacitance of those two kinds of nanotubes is 437.5 F/g and 336.7 F/g under the current density of 1 A/g, respectively. The origin of the electrochemical performance improvement can be attributed to the increased specific surface area and the presence of interlayer ion transport channels in the double-walled hollow structure. The study is very helpful in improving the application prospect of NiCo2O4 material as the electrode material of supercapacitors. Equally important, this study also presents an efficient method to fabricate double-walled hollow nanostructures based on special templates.

Dielectric Screening inside Carbon Nanotubes.

Dielectric screening plays a vital role in determining physical properties at the nanoscale and affects our ability to detect and characterize nanomaterials using optical techniques. We study how dielectric screening changes electromagnetic fields and many-body effects in nanostructures encapsulated inside carbon nanotubes. First, we show that metallic outer walls reduce the scattering intensity of the inner tube by 2 orders of magnitude compared to that of air-suspended inner tubes, in line with our local field calculations. Second, we find that the dielectric shift of the optical transition energies in the inner walls is greater when the outer tube is metallic than when it is semiconducting. The magnitude of the shift suggests that the excitons in small-diameter inner metallic tubes are thermally dissociated at room temperature if the outer tube is also metallic, and in essence, we observe band-to-band transitions in thin metallic double-walled nanotubes.

Direct observation of electron transfer in solids through X-ray crystallography

Nanoscale electron transfer (ET) in solids is fundamental to the design of multifunctional nanomaterials, yet its process is not fully understood. Herein, through X-ray crystallography, we directly observe solid-state ET via a crystal-to-crystal process. We first demonstrate the creation of a robust and flexible electron acceptor/acceptor (A/A) double-wall nanotube crystal ([(Zn2+)4(LA)4(LA=O)4]n) with a large window (0.90 nm × 0.92 nm) through the one-dimensional porous crystallization of heteroleptic Zn4 metallocycles ((Zn2+)4(LA)4(LA=O)4) with two different acceptor ligands (2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridine (LA) and 2,7-bis((1-ethyl-1H-imidazol-2-yl)ethynyl)acridin-9(10H)-one (LA=O)) in a slow-oxidation-associated crystallization procedure. We then achieve the bottom-up construction of the electron donor incorporated-A/A nanotube crystal ([(D)2⊂(Zn2+)4(LA)4(LA=O)4]n) through the subsequent absorption of electron donor guests (D = tetrathiafulvalene (TTF) and ferrocene (Fc)). Finally, we remove electrons from the electron donor guests inside the nanotube crystal through facile ET in the solid state to accumulate holes inside the nanotube crystal ([(D•+)2⊂(Zn2+)4(LA)4(LA=O)4]n), where the solid-state ET process (D – e– → D•+) is thus observed directly by X-ray crystallography.

Structural, electronic, phonon, and elastic properties of zigzag single-walled and double-walled boron nitride nanotubes

The study used Density Functional Theory to simulate the properties of single-walled and double-walled boron nitride nanotubes. The cohesive energy calculations suggest that double-walled nanotubes are more stable than single-walled nanotubes. Double-walled nanotubes have a narrower bandgap than single-walled nanotubes. The smaller diameter of the nanotubes reduces available energy for vibrational modes. Double-walled nanotubes have larger Young’s modulus, shear modulus, and bulk modulus than single-walled nanotubes. Both single-walled and double-walled nanotubes perform like auxetic materials in some directions. The group velocity of acoustic phonons in SWBNNTs (6, 0) is higher than in SWBNNTs (12, 0).

Exploring the structural, electronic, and hydrogen storage properties of hexagonal boron nitride and carbon nanotubes: insights from single-walled to doped double-walled configurations

This study investigates the structural intricacies and properties of single-walled nanotubes (SWNT) and double-walled nanotubes (DWNT) composed of hexagonal boron nitride (BN) and carbon (C). Doping with various atoms including light elements (B, N, O) and heavy metals (Fe, Co, Cu) is taken into account. The optimized configurations of SWNT and DWNT, along with dopant positions, are explored, with a focus on DWNT-BN-C. The stability analysis, employing binding energies, affirms the favorable formation of nanotube structures, with DWNT-C emerging as the most stable compound. Quantum stability assessments reveal significant intramolecular charge transfer in specific configurations. Electronic properties, including charge distribution, electronegativity, and electrical conductivity, are examined, showcasing the impact of doping. Energy gap values highlight the diverse electronic characteristics of the nanotubes. PDOS analysis provides insights into the contribution of atoms to molecular orbitals. UV–Vis absorption spectra unravel the optical transitions, showcasing the influence of nanotube size, dopant type, and location. Hydrogen storage capabilities are explored, with suitable adsorption energies indicating favorable hydrogen adsorption. The desorption temperatures for hydrogen release vary across configurations, with notable enhancements in specific doped DWNT-C variants, suggesting potential applications in high-temperature hydrogen release. Overall, this comprehensive investigation provides valuable insights into the structural, electronic, optical, and hydrogen storage properties of BN and C nanotubes, laying the foundation for tailored applications in electronics and energy storage.

Nonclassical Growth Mechanism of Double-Walled Metal-Oxide Nanotubes Implying Transient Single-Walled Structures.

The formation of imogolite nanotubes is reported to be a kinetic process involving intermediate roof-tile nanostructures. Here, the structural evolution occurring during the synthesis of aluminogermanate double-walled imogolite nanotubes is in situ monitored, thanks to an instrumented autoclave allowing the control of the temperature, the continuous measurement of pH and pressure, and the regular sampling of gas and solution. Chemical analyses confirm the completion of the precursor's conversion with the release of CO2, ethanol, and dioxane as main side products. The combination of microscopic observations, infrared, and absorption spectroscopies with small and wide-angle X-ray scattering experiments unravel a unique growth mechanism implying transient single-walled nanotubes instead of the self-assembly of stacked proto-imogolite tiles. The growth formation of these transient nanotubes is followed at the molecular level by Quick-X-ray absoprtion specotrscopy experiments. Multivariate data analysis evidences that the near neighboring atomic environment of Ge evolves from monotonous to a more complex one as the reaction progresses. The following transformation into a double-walled nanotube takes place at a nearly constant mean radius, as demonstrated by the simulation of X-ray scattering diagrams. Overall, transient nanotubes appear to serve for the anchoring of a new wall, corresponding to a mechanism radically different from that proposed in the literature.

Structure and electrical properties of double-walled silicon nanotubes depending on 585 defects and applied electric fields by SCC-DFTB method

The geometric structural and electronic properties of 585 defective double-walled silicon nanotubes (DWSiNTs) by using the self-consistent charge density functional tight-binding (SCC-DFTB) method. Furthermore, we investigated the impact of external electric field and intensity on the electronic properties. After the relaxation of perfect tubes, the structure of the tube changes significantly, and the winding direction of the tube wall changes. The buckling value of the tube wall is most closely related to the geometric shape and atomic arrangement order of tubes. The overall stability of zigzag tubes is higher than armchair tubes, and (6,6)@(10,10) stability is significantly affected by defects. The partially defected zigzag tubes change from direct band gap semiconductor properties to indirect band gap semi-metal properties. A transformation of the semiconductor-semimetal properties, direct-indirect band gap of DWSiNTs is realized. The charge transfer amplitude of the defect tubes is greater than the perfect tube. The applied electric field makes the stability of all tubes decrease linearly, and the stability of the defect tubes is higher than the perfect tube. Part of the electric field strength changes the defect tubes from semiconductor properties to semi-metal properties, and semi-metal properties to metal properties. These theoretical studies provide a reference for the preparation and future application of DWSiNTs.

Nanotube Slidetronics.

One-dimensional slidetronics is predicted for double-walled boron-nitride nanotubes. Local electrostatic polarization patterns along the body of the nanotube are found to be determined by the nature of the two nanotube walls, their relative configuration, and circumferential faceting modulation during coaxial interwall sliding. By careful choice of chiral indices, chiral polarization patterns can emerge that spiral around the nanotube circumference. The potential usage of the discovered slidetronic effect for low-dimensional nanogenerators is briefly discussed.

Derivation of a Force Field for Computer Simulations of Multi-Walled Nanotubes Using Genetic Algorithm. I. Tungsten Disulfide

A technique for constructing force fields based on the use of genetic algorithms is proposed, which is aimed at parameterization of potentials intended for computer simulation of polyatomic nanosystems. To illustrate the proposed approach, a force field has been developed for modeling layered modifications of WS2, including multi-walled nanotubes, the dimensions of which are beyond the capabilities of ab initio methods. When determining the potential parameters, layered polytypes of bulk crystals, monolayers, bilayers, and nanotubes of small diameters were used as calibration systems. The parameterization found was successfully tested on double-walled nanotubes, the structure of which was determined using density functional calculations. The obtained force field was used for the first time to model the structure and stability of achiral multi-walled nanotubes based on WS2. The interwall distances obtained from the simulation are in good agreement with the results of recent measurements of these parameters for existing nanotubes.

Watching Molecular Nanotubes Self-Assemble in Real Time.

Molecular self-assembly is a fundamental process in nature that can be used to develop novel functional materials for medical and engineering applications. However, their complex mechanisms make the short-lived stages of self-assembly processes extremely hard to reveal. In this article, we track the self-assembly process of a benchmark system, double-walled molecular nanotubes, whose structure is similar to that found in biological and synthetic systems. We selectively dissolved the outer wall of the double-walled system and used the inner wall as a template for the self-reassembly of the outer wall. The reassembly kinetics were followed in real time using a combination of microfluidics, spectroscopy, cryogenic transmission electron microscopy, molecular dynamics simulations, and exciton modeling. We found that the outer wall self-assembles through a transient disordered patchwork structure: first, several patches of different orientations are formed, and only on a longer time scale will the patches interact with each other and assume their final preferred global orientation. The understanding of patch formation and patch reorientation marks a crucial step toward steering self-assembly processes and subsequent material engineering.

Hydrogen-like Impurity States in β-Ga2O3/(AlxGa1−x)2O3 Core/Shell Nanostructures: Comparison between Nanorods and Nanotubes

The binding energy of an off-center hydrogen-like impurity in an ultra-wide band gap β-Ga2O3/(AlxGa1−x)2O3 core/shell nanostructure is studied using a variational method combined with a finite-difference algorithm. Four impurity states with the radial and axial quantum numbers being 0 or 1 in two kinds of core/shell nanostructures, including nanorods and double-walled nanotubes, are taken into account in the numerical calculations. The variation trends in binding energy corresponding to the four impurity states as functions of structural dimension and Al composition differ in nanorods and nanotubes when the impurity moves toward the interface between the Ga2O3 and (AlxGa1−x)2O3 layers. The quantum confinement due to the structural geometry has a considerable influence on the probability density of the impurity states as well as the impurity binding energy. The numerical results will pave the way toward theoretical simulation of the electron states in rapidly developing β-Ga2O3 low-dimensional material systems for optoelectronic device applications.

Effects of Stone-Wales defects on structure and electrical properties of double-walled silicon nanotubes by SCC-DFTB method

In this work, the geometric structure, system stability, electrical properties and charge distribution of zigzag double-walled silicon nanotubes (DWSiNTs) (nin,0)@(nout,0) (nin = 5–7, nout = 8–13) perfect tubes and defective tubes with three types of Stone-Wales (SW) defects were studied using the self-consistent charge density functional tight-binding (SCC-DFTB) method. The change of the chirality index between the inner and outer walls was simulated. The results show that the symmetry of the structure disappears, and the warping of the tube wall changes from order to disorder after introducing SW defects. The warps of outer tube are obviously higher than that of inner tube. The perfect tubes with inner wall chirality index (6,0) are more stable than other tubes. SW defects of outer wall tubes have a higher effect on system stability than those of inner wall tubes. The difference of inner and outer wall chirality indices plays an obvious role in regulating the energy gap of the system, half of which are near-metal properties and the other half semiconductor properties, and the regulation range is 0.1075–0.8519 eV. All types of SW defects at all locations have a certain regulatory effect on the energy gap of DWSiNTs, and the effect of type III defect is the most obvious. The effect of atomic charge redistribution in the tube is related to the structure, and the charge transfer in a perfect tube is symmetrical. The number of electrons obtained at the defect is increased, and the electronegativity is stronger, due to the curvature of local atoms produced at the defect. This study provides a reference for the preparation and future application of DWSiNTs.

Synthesis of Double-Walled Boron Nitride Nanotubes from Ammonia Borane by Thermal Plasma Methods.

Highly crystalline double-walled boron nitride nanotubes (DWBNNTs ∼60%) were synthesized from ammonia borane (AB; H3B-NH3) precursors using a high-temperature thermal plasma method. The differences between the synthesized BNNTs using the hexagonal boron nitride (h-BN) precursor and AB precursor were compared using various techniques such as thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and in situ optical emission spectroscopy (OES). The synthesized BNNTs were longer and had fewer walls when the AB precursor was used than when the conventional method was used (with the h-BN precursor). The production rate significantly improved from ∼20 g/h (h-BN precursor) to ∼50 g/h (AB precursor), and the content of amorphous boron impurities was significantly reduced, implying a self-assembly mechanism of BN radicals rather than the conventional mechanism involving boron nanoballs. Through this mechanism, the BNNT growth, which was accompanied by an increased length, a decreased diameter, and a high growth rate, could be understood. The findings were also supported by in situ OES data. Considering the increased production yield, this synthesis method using AB precursors is expected to make an innovative contribution to the commercialization of BNNTs.

Structural and electronic properties of double-walled zigzag and armchair Zinc oxide nanotubes

• Stability and electronic properties of DWZnONTs based on DFT investigated. • (4,4)@(n,n) and (5,5)@(n,n) and (7,0)@(n,0) and (6,0)@(n,0) DWZnONTs considered. • (n,n)@(n+5,n+5) and 8, (n,0)@(n+8,0) with inter-wall distance of about 4.6 and 4.3 Å are the most stable structures. • All zigzag and armchair nanotubes are semiconductors having a direct bandgap. • Bandgap increases by increasing inner and outer tube diameters and inter-wall distances. • The bandgap of double-walled ZnO nanotubes is smaller than that of their single-walled nanotubes. In this paper, we have investigated the stability and electronic properties of double-walled ZnO nanotubes (DWZnONTs) based on density functional theory (DFT) with the SIESTA package. The calculation have been performed on the armchair (4,4)@(n,n) and (5,5)@(n,n) DWZnONTs with (n=9 to15) and the zigzag (7,0)@(n,0) and (6,0)@(n,0) with (n=14 to 20). The stability calculation of DWZnONTs shows that the armchair and the zigzag DWZnONTs with difference chirality of 5, (n,n)@(n+5,n+5) and 8, (n,0)@(n+8,0) and inter-wall distance of about 4.6 and 4.3 Å are the most stable structures, respectively. Considering the electronic band structure points that all zigzag and armchair nanotubes are semiconductors having a direct bandgap. Moreover, it is revealed that the value of the bandgap increases by increasing inner and outer tube diameters and inter-wall distances, and the process of change at higher inter-wall distances be almost constant. Our results show that the inter-wall coupling diminishes the energy gap in semiconducting DWZnONTs. We found that the energy gap of DWZnONTs depends on the structure of the inner and outer walls. The consequences of this investigation can certainly be helpful in future experimental studies.

Performance study of photocatalytic hydrogen production from ZnO double-walled nanotubes based on density functional theory

The exploration of photocatalytic materials can be an effective measure to deal with the energy crisis and environmental pollution. Based on previous studies, we investigated the geometric and electronic structures of optimized single-walled and double-walled ZnO nanotubes using the hybrid function B3LYP based on density functional theory and calculated the stability and band edge positions of the nanotubes in detail. The calculations show that the band gaps of monolayer, single-walled nanotube (SWNT), and double-walled nanotube (DWNT) are 3.726 eV, 3.722 eV, 3.447 eV, respectively, and it can be seen that the DWNT present the lowest band gap values. At the same time, the bond lengths of ZnO SWNTs and DWNTs are the same as those of ZnO monolayer, and the formation and strain energies of nanotubes decrease with the increase of nanotubes' diameter. The comparison of band edge position and hydrolytic redox potential of ZnO SWNT and DWNT shows that they both have hydrogen production ability. And combined with the smaller band gap value of DWNTs indicating its ability to absorb a broader solar spectrum, we suggest that ZnO DWNTs may exhibit higher catalytic activity than monolayer and SWNTs in photocatalytic hydrogen production.

First-Principle Studies of the Structural, Electronic, and Optical Properties of Double-Walled Carbon Boron Nitride Nanostructures Heterosystem under Various Interwall Distances

Structural, electronic, and optical properties of a new combined system of carbon and boron nitride nanotubes are studied using the DFT first principles as implemented in Quantum ESPRESSO codes. The corrections to the quasi-particle energies were studied via GW hybrid functional implemented in the YAMBO code within the many-body perturbation theory. The studies were performed under different interwall distances of 3.0 nm, 2.5 nm, and 1.5 nm between CNTs and BNNTs. The results showed that the structural properties demonstrated high stability of the double-walled carbon boron nitride nanotube (DWCBNNT) systems under interwall distance (IWD) of 3.00 nm, 2.50 nm, and 1.50 nm. Results also demonstrated an inverse variation between the IWD and the diameter of the DWCBNNT system. In terms of the electronic properties, all three configurations of the DWCBNNTs reveal semiconducting behavior under KS-DFT showing a direct band gap of 3.30 eV, 1.79 eV, and 0.81 eV under IWD of 3.0 nm, 2.5 nm, and 1.5 nm, respectively. Furthermore, the band gap of the DWCBNNT increases with an increase in IWD (decrease in inner tube diameter) and decreases with a decrease in IWD (increase in inner tube diameter). In all three cases, the bands are formed by the molecular orbitals of the armchair CBNNT which are transformed to a series of continuous energy levels; the behaviors of electrons that formed the heterostructure are related to the behavior of electrons in B, C, and N atoms. From the optical properties perspective, the studies were conducted in parallel and perpendicular directions to the nanotubes’ axes. The presence of static dielectric functions in parallel direction at 3.3, 3.4, and 4.5 for nanotubes under 3.0 nm, 2.5 nm, and 1.5 nm demonstrated optical refraction. Refractions were also observed in directions perpendicular to the nanotubes. Furthermore, optical reflections occur when there is a higher absorption. The ability of these CBNNT hybrid systems to refract in all directions revealed the most exciting properties of the armchair CBNNT suitable to be used in magnifying glass materials. The findings further imply that the optical absorption coefficient is inversely related to the diameter of the nanotubes and is directly correlated to the band gap.

Tunable electronic and photocatalytic properties of double-walled γ-GeSe nanotubes: From infrared to visible absorption

Tunable electronic and photocatalytic properties of double-walled γ-GeSe nanotubes: From infrared to visible absorption

Ab initio study of structural properties and inter-wall distances of double-walled BN nanotubes

The structural, stability, and electronic properties and optimized inter-wall distances of double-walled boron nitride nanotubes (DWBNNTs) are investigated based on density functional theory (DFT) with the SIESTA code. The computations are done on the zigzag ([Formula: see text],0)@([Formula: see text],0) DWBNNTs with chirality of ([Formula: see text], 7 and [Formula: see text]–18) and the armchair ([Formula: see text] with chirality of ([Formula: see text], 6 and [Formula: see text]–15). The calculated binding and formation energies revealed that the armchair and the zigzag DWBNNTs with chirality differences of ([Formula: see text] and 9) ([Formula: see text]), ([Formula: see text]) and inter-layer spacing of about 4.22Å and 3.62Å are the best favorable nanotubes, respectively. Analyzing the electronic structures revealed that all considered armchair and zigzag BNNTs are semiconductors. Furthermore, it is concluded that with increasing diameters of the tubes and the spaces between walls, the value of the band gap rises, and the change process is almost constant at larger distances between the walls. Also, compared to single-walled nanotubes, DWBNNTs have a narrower bandgap. Future empirical investigations can definitely benefit from the implications of this research.