Interwall Distance Research Articles

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.

Empirical model for optical transitions in inner semiconducting tubes of double wall carbon nanotubes

The inter-wall distance, average diameter, and chirality of the constituent nanotubes play a significant role in determining the electronic structure of double wall carbon nanotubes (DWNTs). In DWNTs, the inner tube possesses a special status, granted by the outer tube, which acts as a shield. Here, we proposed an empirical model for estimating the different optical transitions of inner semiconducting tubes (ISCTs) of DWNTs from the chirality of the constituent single wall carbon nanotubes when the outer tube can be semiconducting or metallic. So far, there have been no well-known theoretical or empirical models to estimate the optical transitions of ISCTs of DWNTs except first principles simulations. The proposed model relates the optical transitions of ISCTs of DWNTs with the chirality of the inner tube and the average diameter of DWNTs. The relation is used to calculate the optical transitions of a number of ISCTs of DWNTs, and the result was found to be in good agreement with the recent experimental reports. The proposed relation can help understand the electronic behavior of DWNTs in terms of their structural parameters and can help in identifying the chirality of unknown DWNTs from its electronic properties.

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.

Electronic structures and stability of double-walled armchair (n,n)@(m,m) SiC nanotubes

In this work, we have investigated the stability and electronic properties of armchair double-walled SiC nanotubes (DWSiCNTs) based on density functional theory with the SIESTA package. The calculation has been performed on the armchair (4,4)@(n,n) and (5,5)@(n,n) DWSiCNTs with (n = 7–15). The stability calculation of DWSiCNTs shows that the armchair DWSiCNTs with difference chirality of 4, (n,n)@(n + 4,n + 4) and inter-wall distance of 3.65 Å are the most stable structures. Considering the electronic band structure points that all armchair nanotubes are semiconductors with indirect bandgap. Moreover, it is revealed that the value of the bandgap increases by increasing inter-wall distances, and the process of change at higher inter-wall distances be almost constant. In addition, the bandgap of double-walled SiC nanotubes is smaller than that of their single-walled nanotubes. The consequences of this investigation can certainly be helpful in future experimental studies.

Electronic structures and stability of double-walled armchair and zigzag AlN nanotubes

Aluminum-Nitride nanotubes (AlNNTs) are more proper than carbon nanotubes (CNTs) for special applications in Nano electronic and optoelectronic devices. In this work, the stability and electronic properties of double-walled Aluminum-Nitride nanotubes (DWAlNNTs) based on density functional theory (DFT) have investigated. The calculation have performed on the armchair (5,5)@(n,n) and (6,6)@(n,n) DWAlNNTs with (n = 8 to16) and the zigzag (6,0)@(n,0) and (5,0)@(n,0) with (n = 11 to 19). The stability calculation of DWAlNNTs shows that the armchair and the zigzag DWAlNNTs with difference chirality of 7, (n,n)@(n + 7,n + 7) and 12, (n,0)@(n + 12,0) and inter-wall distance of 6 Å are the most stable structures. Moreover, it is revealed that the value of the bandgap increases by increasing inter-wall distances and the bandgap of DWAlNNTs is smaller than that of their single-walled nanotubes. Our results show that the band gap and the stability of AlNNTs are modified by changing the diameter, which is widely application in optoelectronic devices.

On the origin of matter-antimatter asymmetry in the Universe

In order to investigate the origin of matter-antimatter asymmetry in the Universe, we adopt a theoretical framework where the standard model emerges as a Poincaré invariant field theory localized at a domain-antidomain wall (DW-aDW) brane pair of a theory which lives on a higher dimensional bulk. We argue that such a system of a parallel DW-aDW pair could have been created at a very early epoch of the cosmological evolution when the Universe was still of microscopic size because its creation is topologically possible as compared to a single DW creation when the perpendicular extra dimension is compact. The conservation laws, such as of charge and chirality, are not violated in vacuum fluctuations of the combined DW-aDW system, but as we show their simultaneous conservation for each wall separately may not be favorable in certain processes. In particular, as expansion of spacetime occurs in the higher dimensional bulk, the distance d between the DW and the aDW increases as a function of time. We show that during the early stages of the cosmological evolution, when d was of microscopic size, the leading mechanism for pair-creation from fluctuations of the gauge-field with polarization perpendicular to the DWs (i.e., polarization along the extra dimension) was one in which the particle and the antiparticle were created on the opposite domain-walls hosting opposite chirality fermions. This mechanism allows for a matter-antimatter asymmetry to appear separately in the DW and the aDW, while in the combined DW-aDW system no such asymmetry was allowed. Momentum, energy, charge and parity conservation are all fulfilled if we consider the DW-aDW system together. In this scenario, at a later and the present stage of the cosmological evolution, where d is macroscopically large, the probability to violate these conservation laws on a single DW, as a function of the inter-wall distance, is exponentially suppressed.

Hydrodynamic behaviors of self-propelled sperms in confined spaces

ABSTRACT The hydrodynamic behaviors of sperms in confined spaces (e.g. Poiseuille flow and quiescent flow between two parallel walls) are studied with a two-dimensional self-propelled sperm model based on the immersed boundary-lattice Boltzmann method (IB-LBM). For single-sperm swimming in Poiseuille flow, four typical swimming patterns, including wall-adhesion, focusing, tumbling and oscillating, are observed. The occurrence conditions including flow strength, inter-wall distance, initialization of sperm are studied in detail for the four patterns. For multiple-sperm swimming in quiescent flow between two parallel walls, it is observed that the sperm population tends to swim nearby the walls, leading to wall accumulation. To explore the hydrodynamic behaviors of the sperm population in Poiseuille flows, the effects of flow velocities on the sperm rheotaxis and the wall accumulation are investigated in detail. It is found that an appropriate flow velocity is essential to guide the swimming direction, as well as the wall accumulation. In addition, collision and adsorption between adjacent sperms may facilitate wall accumulation. Finally, we study the propulsion rate of different combination modes of sperms. We found that the wedge-shaped mode leads to the optimal propulsive speed, and reducing the combining distance can increase the propulsive speed.

Наклонный волноотражающий козырёк для снижения высоты защитной стенки резервуара типа "стакан в стакане"

Introduction. The prospects for the construction of tanks with a protective wall of the "glass in a glass" type are due to the possibility of their use with increased safety requirements, in particular, when designing near residential areas or water areas. However, previous studies on the retention of fluid flow by a protective wall during the destruction of the internal reservoir have shown that in order to completely retain it, the wall height must be at least 10 % higher than the original liquid level in this tank. It is obvious that the construction of such high protective walls is economically impractical, while conditions can be created for the formation of zones of explosive concentrations both in its inter-wall space and behind the protective wall. In this regard, studies on an effective way to reduce the height by protecting the wall at the maximum level of filling the internal tank with a flammable liquid are relevant. In particular, it is proposed to consider the possibility of arranging on the protective wall an inclined wave-reflective visor facing the wall of the main tank. Goals and objectives. Experimentally prove the possibility of reducing the height of the protective wall of tanks with a protective wall of the "glass in a glass" type by arranging inclined wave-reflective visor on it. Obtain an empirical formula for finding the minimum height of the protective wall depending on the geometric parameters of the main tank, the interwall distance and the outbound length of the wave-reflecting visor. Methods. In the process of research, the methods of similarity theory and hydraulic laboratory modeling, physical experiment, observation, comparison, finding an empirical dependence based on mathematical processing of experimental data, description, generalization were used. Results and their discussion. It has been experimentally proven that the arrangement on the protective wall of inclined wave-reflective visor is an effective method aimed at reducing the height of the protective wall to or below the maximum level of flammable liquid in the main tank. An empirical dependence is obtained to find the optimal ratio between the outbound length of the wave-reflective visor and the inter-wall distance for the main tanks with a protective wall of the "glass in a glass" type, the nominal volume from 700 to 30000 m3. Conclusion. The proposed method of reducing the height of the protective wall and empirical dependence can be the basis for the development of the relevant provisions of the regulatory document on ensuring fire safety of tanks with a protective wall of the "glass in a glass" type, as well as used by design organizations to find optimal solutions for the design and placement of the types of tanks in question at production facilities. Keywords: "glass in a glass" tank, destruction, protective wall, inclined wave-reflective visor, laboratory modeling.

Горизонтальный волноотражающий козырек для снижения высоты защитной стенки резервуара типа «стакан в стакане»

Purpose. The article states the possibility of lowering the protective wall of the “glass-in-glass” tank type thanks to fitting out a horizontal wave-reflecting visor facing the main tank wall. The empirical formula obtained on the basis of the processed experimental data for determining the optimal height of the protective wall depending on the geometrical dimensions of the main tank, interwall distance and length of the wavereflecting visor departure is presented. ABSTRACT Methods. In the process of the research work methods of similarity theory and hydraulic laboratory modeling, physical experiment, observation, comparison, finding empirical dependence based on mathematical processing of experimental data, description and generalization have been used. Findings. It has been found that fitting out a horizontal wave-reflecting visor on the protective wall of a “glass-in-glass” tank type is an effective method aimed at lowering the protective wall height to or below the maximum level of combustible liquid in the main tank. The empirical dependence has been obtained for finding the optimal ratio between the wavelength of the wavereflecting visor and the interwall distance for main tanks with the nominal volume from 700 to 30 000 m3. Research application field. The proposed method of lowering the height of the protective wall and empirical dependence can serve as a background for developing the relevant conditions of the regulatory document on ensuring fire safety of “glass-inglass” tanks type, and it can also be used by engineering companies to find optimal solutions for designing and locating the considered types of tanks. Conclusions. The proposed design solution will allow designing and operating “glass-in-glass” tanks type, providing the standard level of fire safety under observance of compliance with the requirements for stability of protective wall and wavereflecting visor to the hydrodynamic effect of liquid flow and dynamic impact of collapsing structures of the main tank in case of on accident. As an upcoming trend of the research, the fitting of the wave-reflecting visor of an inclined shape on the protective wall in relation to the wall of the main tank can be considered.

Ab Initio Modeling of MultiWall: A General Algorithm First Applied to Carbon Nanotubes.

A general, versatile and automated computational algorithm to design any type of multiwall nanotubes of any chiralities is presented for the first time. It can be applied to rolling up surfaces obtained from cubic, hexagonal, and orthorhombic lattices. Full exploitation of the helical symmetry permits a drastic reduction of the computational cost and therefore opens to the study of realistic systems. As a test case, the structural, electronic, mechanical, and transport properties of multiwall carbon nanotubes (MWCNT) are calculated using a density functional theory approach, and results are compared with those of the corresponding layered (graphene-like) precursors. The interaction between layers has a general minimum for the inter-wall distance of ≈3.4 Å, in good agreement with experimental and computed optimal distances in graphene sheets. The metallic armchair and semiconductor zigzag MWCNT are almost isoenergetic and their stability increases as the number of walls increases. The vibrational fingerprint provides a reliable tool to identify the chirality and the thickness of the nanostructures. Finally, some promising thermoelectric features of the semiconductor MWCNT are reproduced and discussed.

Mechanical, electronic and stability properties of multi-walled beryllium oxide nanotubes and nanopeapods: a density functional theory study.

Single-, double-, and triple-walled beryllium oxide nanotubes (BeONTs) along with BeO nanopeapods were simulated and geometrically optimized under the density functional theory (DFT) framework to investigate their Young's modulus, electronic properties, and stability. We found better properties in single-walled nanotubes, either their electronic or mechanical properties, than other mentioned nanotubes. Increase in the radius and inter-wall distance made an overall decrease in the Young's modulus of SW and DW BeONTs. The highest obtained modulus of SWBeONTs and DWBeONTS was calculated for structures (14,0) and (8,0)@(14,0) with the magnitudes of 700.12Gpa and 712.24Gpa, respectively. In addition, increasing the wall number from one to two resulted to significant growth in Young's modulus of DWBeONTs while created no significant difference between DWBeONTs and TWBeONTs. Bandgap energy of single-walled nanotubes was higher than those of double- and triple-walled nanotubes, and the bandgap showed consistent soar in both SW and DW BeONTs via increase in the radius and inter-wall distance, respectively. Furthermore, considering nanopeapods with various interlayer distances revealed that the Young's modulus and energy gap behavior of these structures were similar to what we observed in SWBeONTs. However, nanopeapods showed weaker mechanical and semiconducting properties compared with SWBeONTs. Moreover, calculating the formation energies of all under consideration structures revealed a reduction of formation energy via an increase in the dimension of single-walled nanotubes, an increase in the dimension of nanotubes via adding more walls, and an increase in the dimension of peapod structures as well, and the bigger structures are more stable than smaller ones.

Magnetostatic dipolar anisotropy energy and anisotropy constants in arrays of ferromagnetic nanowires as a function of their radius and interwall distance

Magnetostatic dipolar anisotropy energy and the total dipolar anisotropy constant, , in periodic arrays of ferromagnetic nanowires have been calculated as a function of the nanowire radius, the interwall distance of the nanowires in the arrays and the geometry of the array (square or hexagonal), by using a realistic atomistic model and the Ewald method. The simulated nanowires have a radius size up to 175 Å that corresponds to 31 500 atoms, and the simulated nanowire arrays have interwall distances between 35 and 3000 Å. The dependence of total magnetostatic dipolar anisotropy constant on the nanowire radius, their interwall distance and the type of array symmetry has been analyzed. The total dipolar anisotropy constant, which is the sum of the intrananowire dipolar anisotropy constant, , due to the dipolar interactions inside an isolated nanowire and the main responsible of the shape anisotropy, and of the internanowire dipolar anisotropy constant, , due to the magnetostatic dipolar interactions among nanowires in the array, have been calculated and compared with the magnetocrystalline anisotropy constant for three nanowire compositions and their crystalline structures. The simulations of the nanowire arrays with large interwall distances have been used to calculate the intrananowire anisotropy constant, , and to analyze the competition between the intrananowire, internanowire and magnetocrystalline anisotropies. According to some magnetic theories, the ratio equals to the areal filling fraction of a nanowire array. Present calculations indicate that the equation for the areal filling fraction matches perfectly for any interwall distance and radius of Ni and Co nanowire arrays. This first equation is used to write a general equation that relates the radius and interwall distance of nanowire arrays with the intrananowire, internanowire and magnetocrystalline anisotropies. This general equation allows to design the geometry of nanowire arrays with the desired orientation of the easy magnetization axis.

Study of the stability and interwall distance of (6,0)@(n,0) double-walled silicon carbide nanotubes by the vdW-DFT method

In this work, the stability and electronic structure of zigzag double-walled silicon carbide nanotubes (DWSiCNTs) (6,0)@(n,0) (with n=11-17) were investigated by using ab initio Van der Waals density functional. By calculating the formation energy and the binding energy of each double walled nanotube, the best interwall distance for the outer nanotube was indicated. The results revealed that (13,0) nanotube could be the best external nanotube for the (6,0) internal nanotube with 3.53 Ainterwall distance to make (6,0)@(13,0) DWSiCNT. The structural calculations also revealed that all studied silicon carbide nanotubes were semiconductors and their energy gap decreased from the single one to the double-walled one. Moreover, with raising the nanotube diameter, the energy gap increased, such that at the most stable double-walled nanotube, its value was about 0.216 eV.

Off-lattice simulation algorithms for athermal chain molecules under extreme confinement

A new algorithmic approach is presented for the generation and successive equilibration of polymer configurations under conditions of extreme confinement where the inter-wall distance, in at least one dimension, approaches the diameter of the spherical monomers. It significantly improves on the Monte Carlo (MC) protocol described in Karayiannis and Laso (2008) [126]. The algorithm is designed to generate highly confined packings of freely-jointed chains of hard spheres of uniform size. Spatial confinement is achieved by including flat, parallel impenetrable walls in one or more dimensions of the simulation box. The present MC scheme allows the systematic study of the effect of chain length, polydispersity, volume fraction, bond tolerance (gap), cell aspect ratio and level of confinement on the short- and long-range structure of polymer chains near and far from the confining planes. In the present study we focus on the efficiency of the MC protocol in generating, equilibrating, and configurationally decorrelating chain assemblies with average lengths ranging from N = 12 to 1000 monomers and at volume fractions from dilute up to the maximally random jammed (MRJ) state. Starting from cubic amorphous cells filled with polymer chains, the MC algorithm is able to reach quasi 2-d (plate-like) and 1-d (tube-like) states under conditions of extreme confinement and/or cell aspect ratio where the inter-wall distance approaches the diameter of beads forming the chains. A comparison with corresponding bulk packings shows the similarities and differences produced by extreme spatial confinement.

Impact of Inter-Wall Distance on Physical Properties of Metal-Semiconducting Double Walled Carbon Nanotube Quantum Dot

Impact of Inter-Wall Distance on Physical Properties of Metal-Semiconducting Double Walled Carbon Nanotube Quantum Dot

Carbon nanotube conditioning part 1—effect of interwall interaction on the electronic band gap of double-walled carbon nanotubes

Ab initio density functional theory simulations were used to calculate the electronic structure and the total energy of double-walled carbon nanotubes (DWCNTs). The relaxed configurations studied were uncapped, infinitely-long zigzag@zigzag double-walled carbon nanotubes. The lowest energy configuration was found to correspond to an interwall distance of 0.35 nm, except for the configurations with inner tube chiral indices (5,0), (6,0) and (7,0). The largest binding energies were found to correspond to a 0.35 nm interwall distance for all the DWCNT configurations studied, and increasing with DWCNT average diameter. In terms of the effect of the interwall interaction on the electronic band gap of DWCNTs, four regions of band gap were obtained which were termed: zero band gap, narrow band gap, small band gap, and medium band gap regions. These regions offer the possibility to first tune the electronic band gap to a region with a desired range, and further tune that choice within the region itself by varying the interwall distance. It was also found that zigzag@zigzag DWCNTs with outer tube leading chiral index n = 3k + 1 or n = 3k + 2 (k being an integer) follow, as a general trend, an inversely proportional relation of the electronic band gap with respect to the average diameter.

Interaction and rheology of vesicle suspensions in confined shear flow

A pair of vesicles sheared between two parallel walls is in an equilibrium state with constant separation increasing with interwall distance. Ordered vesicle suspension is observed in this state. Ordering leads to a decrease of the normalized suspension viscosity with increasing concentration.

Transport and mechanical properties of double-walled carbon nanotubes as a function of interwall distance

ABSTRACTWe present an accurate theoretical technique to investigate electronic, electrical, mechanical and optical characteristic of metal@semiconductor ((4,0)@(8,0)) and metal@metal ((6,0)@(12,0)) double-walled carbon nanotubes. The simulation was conducted in the framework of a combination of DFT and Non-Equilibrium Green's Function (NEGF). The outputs reinforced that by decreasing interwall distance the π-conjugate delocalized electrons movement and the transmission characteristics of these sort of nanotubes are affected. Moreover, the obtained results showed the stability of double-walled CNTs with small interlayer distance due to the compatibility of the rotational symmetry of inner and outer tubes. Nevertheless, the electrical conductivity of (4,0)@(8,0)DWCNTs is extraordinary less than (6,0)@(12,0) DWCNTs and those of their internal and external SWCNTs separately. However, Young's modulus of DWCNTs (4,0)@(8,0) remained in Tetra Pascal range.

Dependence of electron binding energies of semiconducting double walled carbon nanotube on magnetic field and inter-wall distance

In this study the binding energies of semiconducting double walled carbon nanotube (DWCNT) were calculated using the variational method considering the effective mass approximation and confinement potential under external magnetic field. The study reveals that the 2p state splits into three states 2p0, 2p+ and 2p−. The binding energies of 2p+ and 2p− states increases with increase in applied external magnetic field at a given inter-wall distance. Furthermore the binding energies of the states is found to decrease with increase in inter-wall distance and becomes appreciably small (<45 meV) for DWCNT with 0.42 nm inter-wall distance. In addition, our results reveal that for smaller core diameters the electron effective mass increases sharply and attain a peak value around at 0.2 nm and for large tube diameters (>0.8 nm), the electron effective mass becomes constant. The observed results were compared with the previously reported results.

Molecular Dynamics Simulation of Highly Confined Glassy Ionic Liquids

We present a molecular dynamics simulation study of 1-octyl-3-methylimidazolium tricyanomethanide ([Omim+][TCM–]) ionic liquid capped by two silica planar surfaces. The study extends over a wide temperature range and various interwall distances. Our results indicate that the structure and dynamics of the confined system is significantly affected by the width of the film. At the shortest interwall distance of 25 A, which is comparable to the ion pair dimensions, the bulk structure is breached. The dynamics of the cation in the adsorbed layer is accelerated for the time scale of 1 ns and decelerates for longer time scales. In the most confined film, we observe a suppression of the cooperative characteristics in the diffusion. The whole phenomenon seems to be related to an Arrhenius behavior. Our proposed model suggests a stable, static liquid path in the center of the pore that facilitates the diffusion. The simulations results are consistent with a recent experimental study on the same confined system.