Single-walled Zinc Oxide Nanotubes Research Articles

Examining the critical speed and electro-mechanical vibration response of a spinning smart single-walled nanotube via nonlocal strain gradient theory

In this study, the stability and vibration analyses of a spinning smart nanotube under electrical loads are examined for the first time. The smart nanotube structure is made from a single-walled zinc oxide nanotube (SWZnONT) due to its extraordinary piezoelectric and magnetic properties, which have great potential for use as a rotating component in nanoelectromechanical systems (NEMS). To achieve this aim, nonlocal strain gradient theory and Maxwell’s electrostatic equations are used to capture the structure’s small-scale and piezoelectric effects, respectively. In addition, the nanotube’s structural model is based on the Euler–Bernoulli beam theory, deriving governing equations and boundary conditions via the Hamilton principle. A technique employing Galerkin-based closed-form solutions is utilized to solve the equations of motion and get the vibration response of the spinning smart nanotube. Finally, the effects of the material length scale, nonlocal parameter, rotating speed, external voltage, and boundary conditions on natural frequency and critical rotational speed are investigated. The study results indicate that applying an external voltage to spinning SWZnONT effectively adjusts the critical speed and enhances structural stability.

Ferromagnetism in silver-doped single-walled zinc oxide nanotubes

In this paper, the electronic and magnetic properties of single-walled ZnO:Ag nanotubes with a chirality of (6,0) were investigated. Ab initio simulations were carried out using Atomistic ToolKit computer code implementing density functional theory within the local spin density approximation. To obtain an accurate energy band gap for related systems, we used the Hubbard U semiempirical corrections. The introduction of the Ag atom into the ZnO nanotube structure changes the electronic structure, the energy gap decreases with the silver concentration. The calculated value of total magnetic moments of the Ag-doped single-walled ZnO NT system is 1.0 μB. Our results predict that Ag-doped ZnO NT can be a potential candidate for optoelectronic and spintronic devices.

Structural, mechanical, electronic and optical properties of Si decorated zinc oxide nanotube photocatalyst for hydrogen evolution via overall water splitting: A DFT study

This work investigated an Si-doped single-walled zinc oxide nanotube (SWZnONT) as photocatalyst for hydrogen energy production. Photocatalytic properties of the Si-doped SWZnONT were determined based on analysis of structural, electronic and optical absorption spectra using density functional theory. The obtained data for structural and mechanical properties of the systems revealed that Si-doped SWZnONT was stable under 2.7 % and 5.5 % of Si concentrations. Furthermore, the studied SWZnONT doped with 2.7 % Si demonstrated an indirect band gap of 2.6 eV which is desirable to be an ideal photocatalyst. Results from optical spectra analysis revealed that Photo-generated holes on the Si-doped SWZnONT surface promote water splitting.

Structural, Electronic, Vibrational, and Topological Analysis of Single-Walled Zinc Oxide Nanotubes

Single-walled armchair and zigzag ZnO nanotubes (SWZnONTs) have been studied via periodic computational simulations based on density functional theory with the B3LYP, HSE06, PBE0, and PWGGA functional and all-electron basis set. The influence of the diameter of the nanotubes was carried out with respect to the bond length (Zn–O), bond angles (Zn–O–Zn), energy strain, band gap, density of states (DOS), band structures, vibrational analysis, and topological analysis of the electron density according to the quantum theory of atoms in molecules applied to the solid state. Its nanotubes properties were compared with the ZnO bulk and (0001) monolayer surface. The topological analysis, infrared and Raman spectra, and its vibrational modes at increasing diameter are reported for the first time. Owing to these analysis, both chiralities with large diameter can be used interchangeably in semiconductor applications. These theoretical models can be extended to study further issues, such as the effects caused by the addition of dopant and the interaction of molecules inside and/or outside of the nanotube.

Studying the buckling and vibration characteristics of single-walled zinc oxide nanotubes using a nanoscale finite element model

The free vibration and axial buckling of achiral zinc oxide nanotubes (ZnONTs) are studied in this paper based on a three-dimensional finite-element model in which bonds are modeled using beam elements and mass elements are placed at the joints of beams instead of atoms. To determine the mechanical properties of the nanotubes, a linkage is established between molecular mechanics and density functional theory. The fundamental frequency and critical buckling load of ZnONTs with different geometries, chiralities and boundary conditions are calculated. It is shown that zigzag nanotubes are more stable than armchair ones. Investigating the effect of aspect ratio on the critical force shows that longer nanotubes are less stable. Also, it is indicated that increasing the length of the nanotubes will result in decreasing the frequency. Moreover, as the aspect ratio increases, the effect of end conditions diminishes.

Second-order optical response of single-walled zinc oxide nanotubes from first principles calculations

The second-order nonlinear optical susceptibilities of ZnO single-walled nanotubes (SWNTs) were investigated by density functional theory. Both the zigzag and chiral ZnO SWNTs exhibit second-order nonlinear optical response while the armchair ZnO SWNTs have no response of second-order nonlinear optical behaviors. The d33 is the largest component of second-order nonlinear optical susceptibility for both zigzag and chiral ZnO SWNTs, and it decreases as the diameter increase for zigzag ZnO SWNTs. The second-order nonlinear optical susceptibilities mainly originate from electronic transitions from O 2p states in valence bands to Zn 4p states in conduction bands.

Effects of hydrogen adsorption on mechanical properties of chiral single-walled zinc oxide nanotubes

Size- and chirality-dependent mechanical properties of single-walled zinc oxide nanotubes (ZnONTs) under four different states of hydrogen adsorption have been investigated in this paper. A molecular mechanics model is developed to derive analytical expressions for surface Young’s modulus and Poisson’s ratio of chiral hydrogenated ZnONTs (H-ZnONTs). On the basis of quantum mechanics, density functional theory (DFT) is utilized to obtain the force constants of molecular mechanics theory. Also, the values of surface Young’s modulus, bending stiffness, Poisson’s ratio, and atomic structure of a hydrogenated zinc oxide (H-ZnO) sheet associated with the four positions of adsorption are determined via the DFT calculations. The related results indicate that the bending stiffness of a H-ZnO sheet is chirality-independent. The present analysis provides the possibility of considering nanotubes with different types of chirality. It is indicated that, for all positions of hydrogen adsorption, the values of surface Young’s modulus for armchair H-ZnONTs are higher than those of zigzag H-ZnONTs and the results of chiral H-ZnONTs are between the results of armchair and zigzag nanotubes. Also, the maximum stability happens when the hydrogen atoms are adsorbed on zinc and oxygen atoms at the two opposite sides of a ZnO sheet.

First principle study of unzipped zinc oxide nanotubes

First principle calculations have been employed in order to explain the dangling bonds behavior in the rolling up of a zinc oxide nanoribbon (ZnONR) to construct a single-walled zinc oxide nanotube (SWZnONT). Our results show in armchair ZnONR two degenerative dangling bonds split and moved up to higher energies due to symmetry breaking of the system. By more rolling up (increasing the curvature), the energy gap is increased by increasing of curvature.

Ab initio density functional theory investigation of Li-intercalated zinc oxide nanotube bundles

We have investigated the energetic, and geometric and electronic structure of Li-intercalated (5,5) zinc oxide nanotube (ZnONT) bundles via density functional theory as implemented in the code WIEN2k. Our results showed that the most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the ZnONTs. All the Li-intercalated (5,5) ZnONT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial spaces are susceptible for intercalation. The present calculations suggest that the single-walled zinc oxide nanotube (SwZnONT) bundle is a promising candidate for the anode material in battery applications.

First-principles study of the size-dependent structural and electronic properties of thick-walled ZnO nanotubes

The size dependence of atomic relaxations, formation energies, and electronic structures of hexagonal [0001] zinc oxide (ZnO) nanotubes with diameters of up to 2.3 nm were studied using density-functional calculations. The formation energies per Zn–O pair in thick-walled hexagonal ZnO nanotubes were found to be mainly dependent on the wall thickness and not on the tube diameter. Thick-walled ZnO nanotubes are energetically more favorable than single-walled ZnO nanotubes. All ZnO nanotubes were found to be semiconducting, with band gaps larger than that of bulk ZnO. It was also found that the wall thickness of ZnO nanotubes strongly affects their shapes and the energies of the conduction bands, rather than their valence band maxima.

First principles study of the band structure and dielectric function of (6,6) single-walled zinc oxide nanotube

The band structure and dielectric function of a (6,6) single-walled zinc oxide nanotube (SWZONT) have been studied using the first-principles method within the pseudopotential density functional theory (DFT). We find that the (6,6) SWZONT has a direct band gap with an energy gap of 1.91 eV. The valence bands (VBs) are composed of two parts, namely, the low-energy part and the high-energy part. The dielectric function indicates a moderate optical anisotropy in the SWZONT. The magnitude of the peaks in the ε 2( ω) spectrum of dielectric function for the [1 0 0] direction is about half of the magnitude of the corresponding ones for the [0 0 1] direction, which is similar to the case found in single-walled boron nitrogen nanotubes (SWBNNTs). However, the character of dielectric function is different with that of single-walled carbon nanotubes (SWCNTs).

Elasticity and piezoelectricity of zinc oxide crystals, single layers, and possible single-walled nanotubes

The elasticity and piezoelectricity of zinc oxide (ZnO) crystals and single layers are investigated from the first-principles calculations. It is found that a ZnO thin film less than three Zn-O layers prefers a planar graphite-like structure to the wurtzite structure. ZnO single layers are much more flexible than graphite single layers in the elasticity and stronger than boron nitride single layers in the piezoelectricity. Single-walled ZnO nanotubes (SWZONTs) can exist in principle because of their negative binding energy. The piezoelectricity of SWZONTs depends on their chirality. For most ZnO nanotubes except the zigzag type, twists around the tube axis will induce axial polarizations. A possible scheme is proposed to achieve the SWZONTs from the solid-vapor phase process with carbon nanotubes as templates.