Mechanical Properties Of Nanowires Research Articles

Uniaxial deformation of nanowires in 16 refractory multi-principal element alloys

Metallic nanowires are widely employed as small-scale structural materials due to their characteristically small volume and high strength compared with their bulk counterparts. Nowadays, the mechanical properties of nanowires in pure metals are well understood with the help of experiments and simulations. However, the deformation of nanowires in metallic alloys remains elusive. In recent years, a new class of alloys called refractory multi-principal element alloys (RMPEAs) emerged. RMPEAs are alloys that form solid solution phases and consist of three or more principal elements, most of which are refractory metals. In this paper, we perform atomistic simulations to investigate the uniaxial deformation of nanowires in 16 body-centered cubic RMPEAs. For each RMPEA, three nanowires consisting of atoms randomly distributed in three different ways are used. The main finding is that dislocation slips on {110} planes and twinning on {112} planes, respectively, control the compressive and tensile plastic deformation of the nanowires. To provide references, we also study the deformation of nanowires in natural and A-atom potential-based artificial pure metals. Results show that the deformation of RMPEA nanowires cannot be predicted by simply extrapolating from those of pure metal nanowires, highlighting the significance of directly simulating RMPEAs using multiple random atomic structures. It is also found that RMPEAs possess a reduced tension-compression asymmetry compared with pure metals, regardless of the underlying plastic deformation mechanism.

Effect of surface residual stress and surface layer stiffness on mechanical properties of nanowires

Effect of surface residual stress and surface layer stiffness on mechanical properties of nanowires

Mechanical characterization of TiO2 nanowires flexible scaffold by nano-indentation/scratch

Mechanical properties of nanowires (NWs) flexible scaffold biomaterials with open pores and channels are important factors to cell reorganize in growth for tissue regeneration engineering. However, accurate test the mechanical properties of the NWs scaffold is still a challenge because of their flexible property and porous structure. Herein, we measured the mechanical characterizes of TiO2 nanowires (TiO2NWs) flexible scaffold by multi-loads, multi-displacements mixed verification method in nano-indentation/scratch. The results showed that the hardness and Young's modulus of the TiO2NWs flexible scaffold had a certain change rules with a change of the indentation load from 5 μN to 400 μN. Meanwhile, the tangential force of the TiO2NWs flexible scaffold had significantly tensile fracture characteristic under nano-scratch. The multi-loads, multi-displacements mixed verification method by nano-indentation/scratch could be widely applied to measure the mechanical properties of all 3D NWs flexible scaffold nanostructure conveniently and accurately, which is helpful to cover the shortage of bending method for only measure the mechanical properties of 1D nanostructures.

Surface effect on size dependent Young’s modulus of nanowires: Exponentially decreased surface elasticity model

Physical and mechanical properties of nanowires are strongly affected by surface effects. In this letter, a continuum theoretical scheme for describing the elastic property of nanowires was proposed. The influence of surface elasticity was considered as a decreasing regular pattern with increasing distance from surface. The decrease law was considered as exponential in this letter. An imaginary interface (between bulk like core and surface area) of nanowires appears in core-surface and core–shell models. This theoretical model avoided the non-physical interface between bulk like core and surface area of nanowires. The larger exponential decrease factor weakened surface effect obviously and was reflected in the effective Young’s modulus expression. Due to the influence of descending surface elasticity, the second, third, fourth and fifth surface modifications were introduced. This letter is aim to establish a continuum theory for elastic property of nanowires without any sudden change (interface) of Young’s modulus.

Tensile strength and failure mechanism of hcp zirconium nanowires: Effect of diameter, temperature and strain rate

This study is a comprehensive analysis to demonstrate the deformation and failure mechanism of hexagonal Zr nanowires in [0 0 0 1] orientation. Molecular dynamics simulations in conjunction with embedded atom potentials are utilized to determine the effect of the temperature, diameter and strain rate on mechanical properties of nanowire. We have observed two basic scheme that these parameters have different impacts on elastic and plastic deformations of Zr nanowires. The elastic response of nanowire increases by high strain rate, low temperature and small diameter. Although Young’s Modulus can be characterized by strain rate, the temperature and the diameter are more effective key variables in engineering of strength mechanism. On the other hand, high strain rate, low temperature and large diameter decrease the failure of Zr nanowires.

A Review on Size‐Dependent Mechanical Properties of Nanowires

The primary challenge to exploit the nanowire as a truly one‐dimensional building block in nanoscale devices is the clear incorporation of scale effects into the operational performance. Size‐dependent behavior in physical properties of nanowires is the subject of intense experimental and computational studies for more than two decades. In this review, the measurement techniques and computational approaches to study scale effects on mechanical properties of nanowires are reviewed for fcc metallic, silicon, and zinc oxide structures. Advantages and disadvantages of each measurement tool are summarized with data reported in the literature. A similar comparison is carried out for computational techniques. Contradictions in the literature are highlighted with an assessment of research needs and opportunities, among which the plastic behavior of gold nanowires and elastic properties of silicon nanowires can be primarily mentioned. Furthermore, challenges associated with the coupling of measurement methods and modeling approaches are summarized. Finally, points of agreement between experimental measurements and computational studies are discussed paving the way for the utilization of nanowires in future nanoscale devices.

Directional Ostwald Ripening for Producing Aligned Arrays of Nanowires.

The remarkable electronic and mechanical properties of nanowires have great potential for fascinating applications; however, the difficulties of assembling ordered arrays of aligned nanowires over large areas prevent their integration into many practical devices. In this paper, we show that aligned VO2 nanowires form spontaneously after heating a thin V2O5 film on a grooved SiO2 surface. Nanowires grow after complete dewetting of the film, after which there is the formation of supercooled nanodroplets and subsequent Ostwald ripening and coalescence. We investigate the growth mechanism using molecular dynamics simulations of spherical Lennard-Jones particles, and the simulations help explain how the grooved surface produces aligned nanowires. Using this simple synthesis approach, we produce self-aligned, millimeter-long nanowire arrays with uniform metal-insulator transition properties; after their transfer to a polymer substrate, the nanowires act as a highly sensitive array of strain sensors with a very fast response time of several tens of milliseconds.

Superplastic Pd50Pt50 monocrystalline bimetallic alloy nanowire: a molecular dynamics simulation study

We report uniaxial tensile studies of monocrystalline cylindrical Pd50 Pt50 bimetallic alloy nanowire (NW) (11.67 A diameter × 101.14 A length) subjected to strain rates of 1%, 3%, 5%, 8% and 10% ps−1 and temperatures of 100 K, 300 K, 500 K and 700 K using molecular dynamics simulations. The tensile test is carried out along y -axis [0 1 0] with periodic boundary conditions and non-periodic along x -axis and z -axis. Dissipative mechanisms such as dislocations, partial dislocations and stair rod dislocations are also identified during deformation. It is found that NW is sensitive to strain rates and temperatures and exhibits superplastic behavior with strain >100% at higher strain rates. Young's modulus is found to be sensitive to strain rate and temperature and is about 25% less that of bulk value at strain rates >5% ps−1 and at 300 K. Yield strength increases linearly with strain rate and decreases with increase in temperature as expected. Crystalline to amorphous-phase transformations take place at strain rates >5% ps−1 and could be the reason behind large plastic strain. The calculated mechanical properties of NWs will be useful in devices applicable to sensing and catalysis.

The mechanical properties and thermal stability of ultrathin germanium nanowires

The mechanical properties of ultrathin germanium nanowires are investigated: the mechanical properties of the nanowires are severely reduced when temperature increases.

Effects of surface atomistic modification on mechanical properties of gold nanowires

Modulation of the physical and mechanical properties of nanowires is a challenging issue for their technological applications. In this paper, we investigate the effects of surface modification on the mechanical properties of gold nanowires by performing molecular dynamics simulations. It is found that by modifying a small density of silver atoms to the surface of a gold nanowire, the residual surface stress state can be altered, rendering a great improvement of its plastic yield strength. This finding is in good agreement with experimental measurements. The underlying physical mechanisms are analyzed by a core–shell nanowire model. The results are helpful for the design and optimization of advanced nanomaterial with superior mechanical properties.

Coupling effects of stress and ion irradiation on the mechanical behaviors of copper nanowires

By using molecular dynamics simulations, we studied the ion irradiation induced damage in mechanically strained Cu nanowires and evaluated the effects of damage on the mechanical properties of nanowires. The stresses in the pre-strained nanowires can be released significantly by the dislocation emission from the cascade core when the strain is greater than 1%. In addition, comparison of the stress-strain relationships between the defect-free nanowire and the irradiated ones indicates that ion irradiation reduces the yield strength of the Cu nanowires, and both the yield stress and strain decrease with the increase of irradiation energy. The results are consistent with the microscopic mechanism of damage production by ion irradiation and provide quantitative information required for accessing the stability of nanomaterials subjected to mechanical loading and irradiation coupling effects.

Deformation behavior and mechanical properties of amyloid protein nanowires

Amyloid fibrils are most often associated with their pathological role in diseases like Alzheimer’s disease and Parkinson’s disease, but they are now increasingly being considered for uses in functional engineering materials. They are among the stiffest protein fibers known but they are also rather brittle, and it is unclear how this combination of properties affects the behavior of amyloid structures at larger length scales, such as in films, wires or plaques. Using a coarse-grained model for amyloid fibrils, we study the mechanical response of amyloid nanowires and examine fundamental mechanical properties, including mechanisms of deformation and failure under tensile loading. We also explore the effect of varying the breaking strain and adhesion strength of the constituent amyloid fibrils on the properties of the larger structure. We find that deformation in the nanowires is controlled by a combination of fibril sliding and fibril failure and that there exists a transition from brittle to ductile behavior by either increasing the fibril failure strain or decreasing the strength of adhesion between fibrils. Furthermore, our results reveal that the mechanical properties of the nanowires are quite sensitive to changes in the properties of the individual fibrils, and the larger scale structures are found to be more mechanically robust than the constituent fibrils, for all cases considered. More broadly, this work demonstrates the promise of utilizing self-assembled biological building blocks in the development of hierarchical nanomaterials.

Timoshenko Beam Model for Buckling of Nanowires with High-Order Surface Stresses Effects

High-order surface effects can have a significant effect in the mechanical behavior of micro- and nano-sized materials and structures. In the literature the mathematical framework of surface/interface stresses are generally described by generalized Young-Laplace equations based on membrane theory. A refined model of surface stress, counting into surface stresses as well as surface moments, collectively referred to as high-order surface stress, was recently derived by the authors. This framework allows us to simulate the interface between two neighboring media which may have varying in-plane stress through the thickness of the thin membrane. To illustrate surface stress effects, we consider the critical force of axial buckling of nanowires by accounting various degrees of surface stresses. Using the refined Timoshenko beam theory, we incorporate the high-order surface effect in the simulation of axial buckling of nanowires. The results are compared with the solutions based on conventional surface stress model as well as existing experimental data. This study might be helpful to characterize the mechanical properties of nanowires in a wide range of applications.

A continuum model for the mechanical behavior of nanowires including surface and surface-induced initial stresses

The continuum modeling of the mechanical behavior of nanowires has recently attracted much attention due to its simplicity and efficiency. However, there are still some critical issues to be solved. In this paper, we demonstrate the importance of accounting for the effects of initial stresses in the nanowires that are caused by deformation due to surface stresses; we note that such initial stresses have previously been neglected in most existing continuum models. By considering the local geometrical nonlinearity of strains during the incremental flexural motion, a new formulation of the Euler–Bernoulli beam model for nanowires is developed through the incremental deformation theory, in which effects of the surface stress, the surface-induced initial stress and surface elasticity are naturally incorporated. It is found through comparisons to existing experimental and computational results for both fcc metal and ceramic nanowires that the surface-induced initial stresses, which are neglected in the Young–Laplace model, can significantly influence the overall mechanical properties of nanowires. We additionally demonstrate and quantify the errors induced by using the Young–Laplace model due to its approximation of surface stresses acting on only the top and bottom surfaces of nanowires.

Molecular Dynamics Study of Size Effect on Uniaxial Tension of Single Crystal Cu Nanowires

The uniaxial tensions of single crystal Cu nanowires (NWs) with different circular cross-section radiuses are simulated by molecular dynamics (MD) method. Atomic interactions in Cu NWs are described by EAM potential. The results show that the plastic deformation of NWs under uniaxial tension is dominantly controlled by dislocation nucleation and gliding. The mechanical properties of NWs are size-dependent. The NWs with larger radius of cross-section possess higher strength and ductility. Furthermore, the site of neck formation and following break of NWs has strong dependence on size scale of NWs.

Molecular Dynamics Simulation of Mechanical Properties of Single-Crystal Bismuth Telluride Nanowire

The mechanical properties of single-crystal bismuth telluride nanowires have been studied by molecular dynamics methods. The mechanical behavior of the Bi2Te3 nanowire for two principal axes was simulated under different strain rates at low temperature and the results compared with those of bulk Bi2Te3. The simulation results show that, due to its marked anisotropy, the nanowire shows quite different failure behaviors in the two directions, with the failure stress for the a-axis (4.7 GPa) being three times that for the c-axis (1.4 GPa). The stress–strain curve of the nanowire is different from that for Bi2Te3 bulk, as surface stress induced by atomic rearrangement significantly reduces the strength of the nanowire. The effect of strain rate on the mechanical properties of the nanowire has also been analyzed, showing that the failure stress and failure strain decrease with decreasing strain rate, a behavior not apparent in the bulk Bi2Te3 simulation.

Structure-Mechanical Property of Individual Cobalt Oxide Nanowires

We present a comprehensive approach to address the correlation between mechanical properties of nanowires (NWs) with their characteristic size, microstructure, and chemical composition. Using this technique, the Young's modulus of Co3O4 NWs with different sizes was evaluated. Thermal annealing in inert atmosphere was found to induce chemical reduction of as-grown Co3O4 NWs into CoO NWs without modifying their geometrical shape. Both Co3O4 and CoO NWs exhibited a size-dependent variation in Young's modulus.

The coupled effects of geometry and surface orientation on the mechanical properties ofmetal nanowires

We have performed atomistic simulations of the tensile loading of and copper nanowires to investigate the coupled effects of geometry and surface orientation ontheir mechanical behaviour and properties. By varying the nanowire cross section fromsquare to rectangular, nanowires with dominant surface facets are created that exhibitdistinct mechanical properties due to the different inelastic deformation mechanisms thatare activated. In particular, we find that non-square nanowires generally exhibit lower yieldstresses and strains, lower toughness, elevated fracture strains, and a propensity to deformvia twinning; we quantify the links between the observed deformation mechanismsdue to non-square cross section and the resulting mechanical properties, whileillustrating that geometry can be utilized to tailor the mechanical properties ofnanowires.

Stability and Mechanical Properties of Silicon Nanowires

his work focuses on the structure, stability, and mechanical properties of silicon nanowires (SiNWs) oriented along the direction. A total energy calculation and a quenching-technique based on a non-orthogonal tight-binding molecular dynamics (MD) is used to study the equilibrium structure and relative stability of SiNWs of different diameters (d) ranging from 2 nm to 17 nm. Our study of the structural relaxation of wires of different diameters reveal the following two key findings: (i) A SiNW is composed of a crystalline core surrounded by a bond distortion-dominated surface region, and (ii) the width of the surface region is found to be similar to 1 nm and is independent of the diameter of the wire. These findings suggest that there exists a critical diameter (similar to 2 nm) below which a crystalline nanowire becomes unstable due to surface-surface interaction. We have also calculated the surface energy (E-s) for wires of different diameters (d), where the E-s versus d curve exhibits several local minima. A more careful study of the local minimum at d similar to 6 nm finds this minimum to be very sharp. The existence of local minima in the surface energy curve is indicative of themore » existence of magic diameters for SiNWs, while the sharpness of the minima is related to the existence of uniform-diameter wires. A study of the Young's modulus of the similar to 6 nm-SiNW suggests that surface effects are critically important in determining the mechanical properties of nanowires with the value of the Young's modulus reduced from its bulk value by about 40%.« less

Mechanical properties of ultrahigh-strength gold nanowires

Nanowires have attracted considerable interest as nanoscale interconnects and as the active components of both electronic and electromechanical devices. Nanomechanical measurements are a challenge, but remain key to the development and processing of novel nanowire-based devices. Here, we report a general method to measure the spectrum of nanowire mechanical properties based on nanowire bending under the lateral load from an atomic force microscope tip. We find that for Au nanowires, Young's modulus is essentially independent of diameter, whereas the yield strength is largest for the smallest diameter wires, with strengths up to 100 times that of bulk materials, and substantially larger than that reported for bulk nanocrystalline metals (BNMs). In contrast to BNMs, nanowire plasticity is characterized by strain-hardening, demonstrating that dislocation motion and pile-up is still operative down to diameters of 40 nm. Possible origins for the different mechanical properties of nanowires and BNMs are discussed.