Showing papers in "Physica E-low-dimensional Systems & Nanostructures in 2011"

The size-dependent vibration analysis of micro-plates based on a modified couple stress theory

Abstract: A microscale vibration analysis of micro-plates is developed based on a modified couple stress theory. The presence of the length scale parameter in this theory enables us to describe the size effect in micro-structures. A variational approach based on Hamilton’s principle is employed to obtain the governing equations of motion. To illustrate the new model, the free vibration analysis of a rectangular micro plate with two opposite edges simply supported and arbitrary boundary conditions along the other edges and a circular micro-plate are considered. The natural frequencies of micro-plates are presented for over a wide range of length scale parameters, different aspect ratios and various boundary conditions for both rectangular and circular micro-plates. The effect of length scale parameter on natural frequencies of micro-plates are discussed in details and the numerical results reveal that the intrinsic size dependence of material leads to increase the natural frequency.

Extracellular biosynthesis of gold and silver nanoparticles using Krishna tulsi ( Ocimum sanctum) leaf

Abstract: Aqueous extract of Ocimum sanctum leaf is used as reducing agent for the environmentally friendly synthesis of gold and silver nanoparticles. The nanoparticles were characterized using UV–vis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. These methods allow the synthesis of hexagonal gold nanoparticles having size ∼30 nm showing two surface plasmon resonance (SPR) bands by changing the relative concentration of HAuCl4 and the extract. Broadening of SPR is observed at larger quantities of the extract possibly due to biosorption of gold ions. Silver nanoparticles with size in the range 10–20 nm having symmetric SPR band centered around 409 nm are obtained for the colloid synthesized at room temperature at a pH of 8. Crystallinity of the nanoparticles is confirmed from the XRD pattern. Biomolecules responsible for capping are different in gold and silver nanoparticles as evidenced by the FTIR spectra.

Levy type solution method for vibration and buckling of nanoplates using nonlocal elasticity theory

Abstract: In the present study, buckling and vibration of nanoplates are studied using nonlocal elasticity theory. Navier type solution is used for simply supported plates and Levy type method is used for plates with two opposite edge simply supported and remaining ones arbitrary. Results are given for different nonlocality parameter, different length of plates and different boundary conditions. The results show that nonlocality effects should be considered for nanoscale plates. Clamped boundary conditions are more sensitive to nonlocality effects. In the vibration problem nonlocality effects increase with increase in the mode number. Present result can be used for single layer graphene sheets.

Molecular Spintronics

Abstract: Molecular spintronics is recognized to as an attractive new research direction in a field of spintronics, following to metallic spintronics and inorganic semiconductor spintronics, and attracts many people in recent decades The purpose of this manuscript is to describe the history of molecular spintronics by introducing important achievements and to show the current status of this field In addition, the authors briefly introduce several theories for implementing studies in molecular spintronics

Green synthesis of silver and gold nanoparticles using Rosa damascena and its primary application in electrochemistry

Abstract: Biosynthesis and characterizations of nanoparticles have become an important branch of nanotechnology. In this paper, green synthesis of gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using the flower extract of Rosa damascena as a reducing and stabilizing agent, has been discussed. This approach is simple, cost-effective and stable for a long time, reproducible at room temperature and in an eco-friendly manner to obtain a self-assembly of AuNPs and AgNPs. The resulting nanoparticles are characterized using UV–vis, TEM, XRD and FT-IR spectroscopic techniques. A modified glassy carbon electrode using AuNPs (AuNPs/GCE) was investigated by means of cyclic voltammetry in a solution of 0.1 M KCl and 5.0×10−3 M [Fe(CN)6]3−/4−. The results show that electronic transmission rate between the modified electrode and [Fe(CN)6]3−/4− increased.

Green synthesis, characterization and evaluation of biocompatibility of silver nanoparticles

Abstract: Although green synthesis of silver nanoparticles (Ag NPs) by various plants and microorganisms has been reported, the potential of plants as biological materials for the synthesis of nanoparticles and their compatibility to biological systems is yet to be fully explored. In this study, we report a simple green method for the synthesis of Ag NPs using garlic clove extract as a reducing and stabilizing agent. In addition to green synthesis, biological response of Ag NPs in human lung epithelial A549 cells was also assessed. Ag NPs were rapidly synthesized using garlic clove extract and the formation of nanoparticles was observed within 30 min. The green synthesized Ag NPs were characterized using UV–vis spectrum, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X-ray energy-dispersive spectroscopy (EDX) and dynamic light scattering (DLS). Characterization data demonstrated that the particles were crystalline in nature and spherical shaped with an average diameter of 12 nm. Measurements of cell viability, cell membrane integrity and intracellular production of reactive oxygen species have shown that the green synthesized Ag NPs were nontoxic to human lung epithelial A549 cells. This study demonstrated a simple, cost-effective and environmentally benign synthesis of Ag NPs with excellent biocompatibility to human lung epithelial A549 cells. This preliminary in vitro investigation needs to be followed up by future studies with various biological systems.

Theoretical study of the effect of Casimir force, elastic boundary conditions and size dependency on the pull-in instability of beam-type NEMS

Abstract: In this paper, the static pull-in instability of beam-type nano-electromechanical systems (NEMS) is theoretically investigated considering the effect of Casimir attraction, elastic boundary conditions (BC) and size dependency. Rotational springs are utilized at each of the supported ends of the simply and doubly supported beams to model an elastic BC. The modified couple stress theory is applied to examine the size effects on the instability of nanostructures. In order to solve the nonlinear constitutive equation of nano-beams, modified Adomian decomposition (MAD) as well as the numerical method is employed. The results reveal significant influences of Casimir attraction, elastic BC and size dependency on the pull-in characteristics of NEMS. The obtained MAD solution agrees well with the numerical one.

Axisymmetric buckling of the circular graphene sheets with the nonlocal continuum plate model

Abstract: In this article, the buckling behavior of nanoscale circular plates under uniform radial compression is studied. Small-scale effect is taken into consideration. Using nonlocal elasticity theory the governing equations are derived for the circular single-layered graphene sheets (SLGS). Explicit expressions for the buckling loads are obtained for clamped and simply supported boundary conditions. It is shown that nonlocal effects play an important role in the buckling of circular nanoplates. The effects of the small scale on the buckling loads considering various parameters such as the radius of the plate and mode numbers are investigated.

Buckling analysis of variable thickness nanoplates using nonlocal continuum mechanics

Abstract: This paper presents an investigation on the buckling characteristics of nanoscale rectangular plates under bi-axial compression considering non-uniformity in the thickness. Based on the nonlocal continuum mechanics, governing differential equations are derived. Numerical solutions for the buckling loads are obtained using the Galerkin method. The present study shows that the buckling behaviors of single-layered graphene sheets (SLGSs) are strongly sensitive to the nonlocal and non-uniform parameters. The influence of percentage change of thickness on the stability of SLGSs is more significant in the strip-type nonoplates (nanoribbons) than in the square-type nanoplates.

Thermal effect on free vibration and buckling of size-dependent microbeams

Abstract: Based on the modified couple stress theory, free vibration and buckling of the microbeams with the effect of the temperature change are investigated. The non-classical Timoshenko beam model, which contains a material length scale parameter, is developed to interpret the size effect in microscale structures. The higher-order governing equations and boundary conditions are derived by using the Hamilton principle. The differential quadrature method is employed to determine the natural frequency and the critical buckling load of the microbeams with different boundary conditions. The effects of the temperature change, length scale parameter, slenderness ratio and end supported conditions on the free vibration and buckling of the microbeams are discussed in detail. Results show that the thermal effect on the fundamental frequency and critical buckling load is slight when the thickness of the microbeam has a similar value to the material length scale parameter, but it becomes significant when the thickness of the microbeams becomes larger.

Modeling carbon nanotube-based mass sensors using axial vibration and nonlocal elasticity

Abstract: In the present study, axial vibration behavior of single-walled carbon nanotube-based mass sensors is studied using nonlocal elasticity theory. The nonlocal constitutive equations of Eringen are used in the formulations. Carbon nanotubes with different lengths, attached mass and boundary conditions are considered in the formulations. The effects of nonlocality, length of the carbon nanotubes and attached mass are investigated in detail for each considered problem. It is shown that the axial vibration behavior of single-walled carbon nanotubes can be used in mass sensors. The dynamic behavior of single-walled carbon nanotubes can be modeled using the nonlocal elasticity models. The mass sensitivity of nanotube-based mass sensors can reach zeptograms.

Flow-induced vibration and instability of embedded double-walled carbon nanotubes based on a modified couple stress theory

Abstract: Vibration and instability of fluid-conveying double-walled carbon nanotubes (DWNTs) are investigated in this paper based on the modified couple stress theory and the Timoshenko beam theory. The microstructure-dependent Timoshenko beam model, which contains a material length scale parameter and can take the size effect into account, is employed. The Poisson's ratio effect is also included in this model. The surrounding elastic medium is described as the Winkler model characterized by the spring. The higher-order governing equations and boundary conditions are derived by using Hamilton's principle. The differential quadrature (DQ) method is employed to discretize the governing equations, which are then solved to obtain the resonant frequencies of fluid-conveying DWNTs with different boundary conditions. A detailed parametric study is conducted to study the influences of length scale parameter, Poisson's ratio, spring constant, aspect ratio of the DWNTs, velocity of the fluid and end supports on the vibration and flow-induced instability of DWNTs. Results show that the imaginary component of the frequency and the critical flow velocity of the fluid-conveying DWNTs increase with increase in the length scale parameter.

Computational study of CO and NO adsorption on magnesium oxide nanotubes

Abstract: The adsorption of CO and NO molecules on the MgO nanotubes was investigated using density functional theory calculations. The adsorption energies of CO and NO were estimated to ranging from −0.35 to −0.16 eV and −0.28 to −0.13 eV, respectively. The most stable adsorption configurations are those in which the C or N atoms the adsorbates are close to the Mg atom of the tube surface. It was found that the MgO nanotubes selectively act against the CO and NO gaseous molecules. Their electrical conductivity are sensitive to NO gaseous molecule while is not to CO one, indicating that they may be potential sensors for NO molecule. These findings are characterized by analyzing the features in the electron density of states.

Band gap engineering of nanostructure Cu doped CdO films

Abstract: Nanostructured Cu doped CdO films were fabricated using the sol–gel spin coating technique. Surface morphology and particle size of the films were studied by atomic force microscopy. Atomic force microscopy study revealed that the particle size of the films is a nanometers and particle size is decreased with increase in Cu doping levels. The band gap of the CdO film was found to decrease by Cu doping. Among the Cu doped CdO films, the band gap was observed to increase with increase in Cu doping level. The effect of particle size on the widening of the band gap was observed for Cu doped films. The observed increase in the band gap is explained on the basis of quantum size effects.

Interaction of NH3 with aluminum nitride nanotube: Electrostatic vs. covalent

Abstract: The interaction of NH 3 with aluminum nitride nanotubes (AlNNTs) has been investigated on the basis of density functional theory calculations. Unlike the case of carbon nanotubes, it was found that the NH 3 can be chemically adsorbed on the top of the aluminum atom of AlNNTs. The NH 3 adsorption energy of AlNNTs is typically more than that of BNNTs. Despite the strong interaction, the chemical modification of AlNNTs with the NH 3 results in little changes in the electronic properties of AlNNTs. Morokuma, NBO and density of states analyses reveal that the nature of this interaction is mainly electrostatic rather than covalent.

Nonlocal Timoshenko beam model for the large-amplitude vibrations of embedded multiwalled carbon nanotubes including thermal effects

Abstract: A nonlocal Timoshenko beam model is developed to study the nonlinear vibrations of embedded multiwalled carbon nanotubes (MWCNTs) in thermal environments. The Timoshenko beam model, unlike its Bernoulli–Euler beam counterpart, takes the effects of transverse shear deformation and rotary inertia into consideration. These effects become more significant for short-length nanotubes that are normally encountered in applications such as nanoprobes. The nested nanotubes are coupled via the van der Waals (vdW) force that considers interactions between adjacent and non-adjacent nested nanotubes. The set of coupled nonlinear equations are then analytically solved using the harmonic balance approach. The effects of small-scale parameter, nanotube geometries, temperature change and the elastic medium are investigated.

Vibration of nanoscale plates with surface energy via nonlocal elasticity

Abstract: The vibration behaviors of simply supported Kirchhoff and Mindlin nanoscale plates with consideration of surface effects are studied using the nonlocal elastic theory. The motion equations of the nanoplates are obtained and the closed form solutions for natural frequency are established using Navier's approach. According to the analysis, the influences of surface energy and nonlocal effect on natural frequency of the nanoplates are very significant. The surface energy increases the natural frequency but the nonlocal parameter decreases the natural frequency. The influence of nonlocal effect becomes increasingly pronounced for higher order vibration modes. On the contrast, the effect of surface energy is important at lower frequencies.

Buckling analysis of micro/nanoscale plates via nonlocal elasticity theory

Abstract: The present study proposes an analytical solution for the buckling analysis of rectangular nanoplates. In order to extract characteristic equations of the micro/nanoscale plate under in-plane load, the analysis procedure is based on the nonlocal Mindlin plate theory considering the small scale effects. The nonlocal Mindlin plate theory allows for small scale effects. The results show that buckling loads of biaxially compressed micro/nanoscale plate depend on the nonlocal parameter. In addition, the effects of small length scale on buckling loads are graphically presented for different geometrical parameters such as aspect ratios and loading factors. This study might be useful for the design of nanoelectronic devices such as atomic dust detectors and biological sensors.

Free vibration analysis of functionally graded carbon nanotubes with variable thickness by differential quadrature method

Abstract: Free vibration analysis of functionally graded carbon nanotube with variable thickness based on the Timoshenko beam theory is investigated. The material properties are assumed to be graded in the longitudinal direction, which vary according to a simple power law distribution. The differential quadrature method (DQM) is adopted to solve the equations of motion. It can be mentioned that results for free vibration analyses of the functionally graded carbon nanotube with variable thickness by differential quadrature method are not available yet and the results may be used as benchmark for future works.

UV detecting properties of hydrothermal synthesized ZnO nanorods

Abstract: The photoresponse behavior of one-dimensional ZnO nanorods grown on ZnO-coated glass substrates via a wet-chemical route at low temperature of 70 °C was investigated. The morphology, structure, composition and chemical state of the prepared nanostructures were characterized by SEM, AFM, XRD and XPS measurements, respectively. The ZnO 1D nanostructures were found to have a hexagonal crystalline structure and grown along the [0 0 1] direction. The nanorods were about 1 μm in length and lower than 100 nm in diameter. The changes in photoresponse of the ZnO nanorods were investigated under different powers of UV illumination and it was also shown that the nanorods have a high sensitivity to UV light. The study suggested that the photoresponse originated from bulk and surface related processes. It is believed that the synthesized ZnO nanorods can be potentially useful in the designing of 1D ZnO-based optoelectronic devices.

Enhanced Kerr nonlinearity in a tunnel-coupled double quantum wells

Abstract: The giant Kerr nonlinearity in an asymmetric coupled quantum well (CQW) driven by probe and control laser fields based on intersubband transitions is investigated. The effect of controlling parameters such as intensity of coupling field and electron tunneling on nonlinear behavior of the system is then discussed. It is shown that the enhanced Kerr nonlinearity with reduced linear and nonlinear absorption can be achieved.

Flow-thermoelastic vibration and instability analysis of viscoelastic carbon nanotubes embedded in viscous fluid

Abstract: The flexural vibration of viscoelastic carbon nanotubes (CNTs) conveying fluid and embedded in viscous fluid is investigated by the nonlocal Timoshenko beam model. The governing equations are developed by Hamilton's principle, including the effects of structural damping of the CNT, internal moving fluid, external viscous fluid, temperature change and nonlocal parameter. Applying Galerkin’s approach, the resulting equations are transformed into a set of eigenvalue equations. The validity of the present analysis is confirmed by comparing the results with those obtained in literature. The effects of the main parameters on the vibration characteristics of the CNT are also elucidated. Most results presented in the present investigation have been absent from the literature for the vibration and instability of the CNT conveying fluid.

Carbon nanotubes film based temperature sensors

Abstract: This study presents the design and fabrication of carbon nanotubes (CNTs) film based temperature sensor. The sensor has been fabricated by the sequential deposition of thin layers of glue and CNT nanopowder on a paper substrate. The diameter of multiwalled nanotubes (MWNTs) varied between 10 and 30 nm. The ostensible thickness of the CNT films in the samples was ∼30–40 μm. The inter-electrodes distance (length) and width of the surface-type samples were 5 and 4 mm, respectively. The results revealed that the DC resistance of the sensors decreases in average by 10–20% as the temperature increases from 20 to 75 °C. The resistance–temperature relationship was simulated.

Exact nonlocal solution for postbuckling of single-walled carbon nanotubes

Abstract: The purpose of this paper is to present exact and efficient analytical expressions for the postbuckling configurations of single-walled carbon nanotubes with different boundary conditions. The nonlinear governing partial-integral differential equations are derived based on Eringen's nonlocal elasticity model and the Euler–Bernoulli beam theory. The geometric nonlinearity is taken into account, which arises from the mid-plane stretching. The exact nonlocal model results can be conveniently used to assess the sensitivity of the small-scale parameter on the nanotubes postbuckling load–deflection relationship. The accuracy of the solution is demonstrated by comparing the critical buckling load results with those available in literature. The influences of small-scale parameter, various end conditions as well as nonlinearity on the postbuckling deformation are examined.

Optical rectification coefficient of a two-dimensional quantum pseudodot system

Abstract: Optical rectification coefficient associated with intersubband transitions in a two-dimensional quantum pseudodot system, under the influence of an uniform magnetic field is theoretically investigated. In this regard, the compact-density matrix approach and an iterative method are used to find the optical rectification coefficient of the pseudodot system. We have investigated the effects of an external magnetic field, the geometrical size and the chemical potential of the pseudodot system on this coefficient. It is found that optical rectification coefficient is affected by the external magnetic field, the geometrical size and the chemical potential of the pseudodot system.

Critical buckling temperature of single-walled carbon nanotubes embedded in a one-parameter elastic medium based on nonlocal continuum mechanics

Abstract: In this paper, the critical budding temperature of single-walled carbon nanotubes (SWCNTs), which are embedded in one-parameter elastic medium (Winkler foundation) is estimated under the umbrella of continuum mechanics theory. Nonlocal continuum theory is incorporated into Timoshenko beam model and the governing differential equations of motion are derived. An explicit expression for the non-dimensional critical buckling temperature is also derived in this work. The effect of the nonlocal small scale coefficient, the Winkler foundation parameter and the ratio of the length to the diameter on the critical buckling temperature is investigated in detail. It can be observed that the effects of nonlocal small scale parameter and the Winkler foundation parameter are significant and should be considered for thermal analysis of SWCNTs. The results presented in this paper can provide useful guidance for the study and design of the next generation of nanodevices that make use of the thermal buckling properties of embedded single-walled carbon nanotubes. (C) 2011 Elsevier B.V. All rights reserved.

Torsional vibration of carbon nanotube–buckyball systems based on nonlocal elasticity theory

Abstract: In this paper, torsional vibration analysis of single-walled carbon nanotube–buckyball systems is carried out The buckyball is attached to single-walled carbon nanotube (SWCNT) at one end and the other end of SWCNT is fixed Such nanostructures are promising for tunable nanoresonators whose frequency can be altered by attaching different buckyballs Nonlocal elasticity is utilized to examine the small-scale effect on the nanoresonators and derive the torsional frequency equation and nonlocal transcendental equation Based on these equations, numerical results are obtained for the dependence of the frequency on the mass moment of inertia The analytical expressions of nonlocal frequencies are also derived when the buckyballs mass moment of inertias are much larger than that of SWCNTs In addition, effort is made to study the influence of nonlocal parameter and attached buckyball on the torsional frequency of the nanoresonators

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

Abstract: In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.

A modified nonlocal beam model for vibration and stability of nanotubes conveying fluid

Abstract: In this paper, a new, modified nonlocal beam model is developed for analyzing the vibration and stability of nanotubes conveying fluid, in which one single nonlocal nanoscale parameter is included. Using Hamilton’s principle, a new higher-order differential equation of motion and the corresponding higher-order, non-classical boundary conditions are obtained for nanotubes conveying fluid. Based on this modified nonlocal model, effect of nonlocal nanoscale parameter on natural frequencies and critical flow velocities is presented and discussed through numerical calculations. It is found that this factor has great influence on the vibration and stability of nanotubes conveying fluid. In particular, the nonlocal effect tends to induce higher natural frequencies and higher critical flow velocities as compared to the results obtained from the classical and partial nonlocal beam models.

Terahertz wave propagation in uniform nanorods: A nonlocal continuum mechanics formulation including the effect of lateral inertia

Abstract: The dynamic testing of materials and components often involves predicting the propagation of stress waves in slender rods. The present work deals with the analysis of the wave propagation characteristics of nanorods. The nonlocal elasticity theory and also the lateral inertia are incorporated into classical/local rod model to capture unique features of the nanorods under the umbrella of continuum mechanics theory. The strong effect of the nonlocal scale has been obtained which leads to substantially different wave behaviors of nanorods from those of macroscopic rods. Nonlocal rod/bar model is developed for nanorods including the lateral inertia effects. The analysis shows that the wave characteristics are highly over estimated by the classical rod model, which ignores the effect of small-length scale. The wave propagation properties of the nanorod obtained from the present formulations are compared with the continuum rod model, nonlocal second and fourth order strain gradient models, Born-K a ´ rm a ´ n model and the nonlocal stress gradient model. It has also been shown that, the unstable second order strain gradient model can be replaced by considering the inertia gradient terms in the formulations. The effects of both the nonlocal scale and the diameter of the nanorod on spectrum curves are highlighted in the present manuscript. The results provided in this article are useful guidance for the study and design of the next generation of nanodevices that make use of the wave propagation properties of single-walled carbon nanotubes.