Deformation 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.

Deformation of nanowires and nanotubes

In this article, we have investigated the consequences of the next-to-leading-order correction to the effective field theory of nanostructures. This has been done by analyzing the effects of deformed Heisenberg algebra on nanowires and nanotubes. We first deform the Schrödinger equation with cylindrical topology. Then specific solutions to the deformed Schrödinger equation with different boundary conditions are studied. These deformed solutions are used to investigate the consequences of the deformation on the energy of nanowires and nanotubes. This deformation can be detected by connecting such nanostructures to ferromagnets, and testing the current-voltage relation for such junctions.

Lightweight and Strong Ceramic Network with Exceptional Damage Tolerance.

Lightweight materials such as porous ceramics have attracted increasing attention for applications in energy conservation, aerospace and automobile industries. However, porous ceramics are usually weak and brittle; in particular, tiny defects could cause catastrophic failure, which affects their reliability and limits the potential use greatly. Here we report a SiC/SiO2 nanowire network constructed from numerous well-bonded SiC nanowires coated by a biphasic structure consisting of amorphous SiO2 and nanocrystal SiC. The as-obtained SiC/SiO2 nanowire network is lightweight (360 ± 10 mg cm-3), mechanically strong (compressive strength of 16 MPa), and damage-tolerant. The high strength of the network is attributed to the biphasic mixed structure of the binding coating which can restrict the deformation of nanowires upon compression. The lightweight and strong SiC/SiO2 nanowire network shows potential for engineering applications in harsh environments.

Deformation of Copper Nanowire under Coupled Tension-Torsion Loading.

Metallic nanowires (NWs) are essential building blocks for flexible electronics, and experience different deformation modes due to external mechanical loading. Using atomistic simulations, this work investigated the deformation behavior of copper nanowire under coupled tension–torsion loading. A transition in both yielding pattern and dislocation pattern were observed with varying torsion/tension strain ratios. Specifically, increasing the torsion/tension strain ratio (with larger torsional strain) triggered the nucleation of different partial dislocations in the slip system. At low torsion/tension strain ratios, plastic deformation of the nanowire was dominated by stacking faults with trailing partial dislocations pinned at the surface, shifting to two partial dislocations with stacking faults as the strain ratio increases. More interestingly, the NW under tension-dominated loading exhibited a stacking fault structure after yielding, whereas torsion-dominated loading resulted in a three-dimensional dislocation network within the structure. This work thus suggests that the deformation behavior of the NW varies depending on the coupled mechanical loading, which could be beneficial for various engineering applications.

Designing anisotropic inorganic nanocapsules via self-assembly of polymer-like ultrathin Au nanowires.

Anisotropic assembly of nanomaterials into hollow structures is an attractive technique in biomedicine and biosensing. Commonly used polymer materials are easy to assemble yet it is hard to form anisotropic morphologies. Here in this work, we successfully prepared a novel gold nanocapsule with an anisotropic ellipsoidal shape and cavity structure by the self-assembly of ultrathin Au nanowires. The assembly mechanism is further studied by tuning the assembly conditions such as nanowire concentration, solvent composition, and temperature. It is found that the controlling forces of the nanowire assembly process are mainly the symmetric interfacial tension and the asymmetric nanowire deformation potential, which contribute together to result in anisotropic nanocapsules. Finally, the obtained Au nanocapsules were used as nanocarriers to load pyrene as a model drug, showing great drug loading ability and pH-responsive drug release behavior. We believe that this unique anisotropic assembly product will bring new insights into nanostructure design and soft matter research.

Atomic-scale simulation of nanojoining of Cu-Ag core-shell nanowires

Effective fabrication methods of Cu-Ag core-shell nanowires network are of vital importance for their shining applications in stretchable electronics. In this study, molecular dynamics simulations are performed to study nanojoining of Cu-Ag core-shell nanowires by head-to-head cold welding, along with mechanical properties of obtained welding joints. Results show that Cu-Ag core-shell nanowires can be successfully connected by cold welding with high-efficiency and few defects owing to atomic interaction and diffusion of atoms. What's more, welding velocity and remaining deformation in nanowires will exert significant influence on mechanical properties of joints, including strength and plasticity. It is revealed that cold welding under pressure will somewhat cause internal compression of structures which can be alleviated by following tensile deformation of the two heads if possible. These findings deepen the understanding of nanoscale cold welding and are expected to provide practical reference for the bottom-up fabrication and assembly of Cu-Ag core-shell nanowires network.

Energy-dispersive X-ray micro Laue diffraction on a bent gold nanowire.

This article reports on energy-dispersive micro Laue (µLaue) diffraction of an individual gold nanowire that was mechanically deformed in three-point bending geometry using an atomic force microscope. The nanowire deformation was investigated by scanning the focused polychromatic X-ray beam along the nanowire and recording µLaue diffraction patterns using an energy-sensitive pnCCD detector that permits measurement of the angular positions of the Laue spots and the energies of the diffracted X-rays simultaneously. The plastic deformation of the nanowire was shown by a bending of up to 3.0 ± 0.1°, a torsion of up to 0.3 ± 0.1° and a maximum deformation depth of 80 ± 5 nm close to the position where the mechanical load was applied. In addition, extended Laue spots in the vicinity of one of the clamping points indicated the storage of geometrically necessary dislocations with a density of 7.5 × 1013 m-2. While µLaue diffraction with a non-energy-sensitive detector only gives access to the deviatoric strain, the energy sensitivity of the employed pnCCD offers absolute strain measurements with a resolution of 1%. Here, the residual strain after complete unloading of the nanowire amounted to maximum tensile and compressive strains of the order of +1.2 and -3%, which is comparable to the actual resolution limit. The combination of white-beam µLaue diffraction using an energy-sensitive pixel detector with nano-mechanical testing opens up new possibilities for the study of mechanical behavior at the nanoscale.

Interfacial shear stress transfer at nanowire-polymer interfaces with van der Waals interactions and chemical bonding

Interfacial mechanics between nanostructures and matrix is of critical importance for a range of device applications of the nanostructures. However, it is challenging to characterize interfacial shear stress transfer at such nanoscale interfaces. In this work, we report a new method to study the interfacial shear stress transfer of single Si nanowires on top of a polymer substrate that is subjected to uniaxial tensile loading. In-situ atomic force microscopy (AFM) testing is used to measure the nanowire deformation, more specifically, average axial strain, as a function of the applied strain to the substrate. Two types of substrates, as-prepared and chemically treated, are selected to examine the effect of van der Waals interactions and chemical bonding. It is found that nonlinear and bilinear cohesive shear-lag models can well capture the interfacial shear stress transfer characteristics associated with the two types of interactions, respectively. For each type, the interface parameters such as interfacial stiffness, shear strength, and/or fracture toughness are identified by fitting the experimental results. This work provides valuable insights into fundamental mechanisms underlying the interfacial shear-lag models. In addition, a parametric study with different nanowire dimensions is carried out, which can provide a guide to experimental design of elastic strain engineering and fracture of Si nanowires.

Nanoscale Mechanosensing of Natural Killer Cells is Revealed by Antigen-Functionalized Nanowires.

Cells sense their environment by transducing mechanical stimuli into biochemical signals. Commonly used tools to study cell mechanosensing provide limited spatial and force resolution. Here, a novel nanowire-based platform for monitoring cell forces is reported. Nanowires are functionalized with ligands for cell immunoreceptors, and they are used to explore the mechanosensitivity of natural killer (NK) cells. In particular, it is found that NK cells apply centripetal forces to nanowires, and that the nanowires stimulate cell contraction. Based on the nanowire deformation, it is calculated that cells apply forces of down to 10 pN, which is the smallest value demonstrated so far by microstructured platforms for cell spreading. Furthermore, the roles of: i) nanowire topography and ii) activating ligands in the cell immune function are studied and it is found that only their combination produces enhanced population of activated NK cells. Thus, a mechanosensing mechanism of NK cells is proposed, by which they integrate biochemical and mechanical stimuli into a decision-making machinery analogous to the AND logic gate, whose output is the immune activation. This work reveals unprecedented mechanical aspects of NK cell immune function and introduces an innovative nanomaterial for studying cellular mechanics with unparalleled spatial and mechanical resolution.

Elastic deformation behavior and microstructure evolution of single crystal nickel nanowire in tensile test along [0 0 1] orientation

Elastic deformation behavior and microstructure evolution of single crystal nickel nanowire in tensile test have been investigated using molecular dynamics simulations. When the temperature is above 300 K, the deformation of nanowire is inhomogeneous in the elastic stage. It can generate a kind of (body-centered cubic)-like structure within the material to guide the elastic deformation, rather than the uniform deformation of all the atoms. The (body-centered cubic)-like structure will transform to be a body-centered cubic structure gradually with the increasing of strain and will revert to be a face-centered cubic structure when the twin crystal appears. The formation of (body-centered cubic)-like structure could reduce the density of the material to resist deformation. Besides, the (body-centered cubic)-like structure increase with increasing of strain or temperature, and they will gather together to reduce the interface energy. Our conclusion also can be proved by the radial distribution functions g(r).

GaAs Wurtzite Nanowires for Hybrid Piezoelectric Solar Cells

The properties of the hybrid energy sources “piezoelectric nanogenerator-solar cell” based on GaAs nanowires with the wurtzite crystal structure were investigated. Measurements were performed by the bending of the nanowire by the probe of the atomic force microscope with simultaneous recording of short circuit current in dark and illuminated conditions. We show that a piezoelectric current pulse of ~10 pA arises in the “nanowire-probe” circuit during the deformation of nanowire by the AFM probe. Under laser illumination, the value of the pulse increases by two orders of magnitude as a result of the piezophototronic effect. Deformation of the nanowire boosts the photocurrent by 40% up to 0.5 nA.

GaAs wurtzite nanowires for hybrid piezoelectric solar cells

AbstractThe properties of the hybrid energy sources “piezoelectric nanogenerator-solar cell” based on GaAs nanowires with the wurtzite crystal structure were investigated. Measurements were performed by the bending of the nanowire by the probe of the atomic force microscope with simultaneous recording of short circuit current in dark and illuminated conditions. We show that a piezoelectric current pulse of ~10 pA arises in the “nanowire-probe” circuit during the deformation of nanowire by the AFM probe. Under laser illumination, the value of the pulse increases by two orders of magnitude as a result of the piezophototronic effect. Deformation of the nanowire boosts the photocurrent by 40% up to 0.5 nA.

Features of structural transformations of HCP metallic Ti nanowires using Cleri-Rosato potential at low temperature

A molecular dynamics (MD) simulation deformation of nanowires under uniaxial tensile strain condition for HCP Ti single crystals is performed in order to clarify the dependence of the deformation behavior of the nanowires from tension. Simulations are performed using tight-binding model (the Cleri-Rosato potential). A computer experiment is performed at a temperature 10 K. Diagrams of stored energy obtained at various time by the MD simulations of the tensile specimens of these metallic Ti nanowires show a rapid increase in stress up to a maximum followed by a gradual drop to zero when the specimen fails by ductile fracture. Features of stored energy changing can be divided into three regions: quasi-elastic, plastic and failure. These transformations are characterized by various structural features that manifest in the nature of the change curve of the stored strain energy and the emergence of various types of structural defects. The results showed that breaking position depended on the nanowire length. It seems that the use of Clery-Rozato potential possible to obtain sufficiently reliable representation of the behavior of nanometalic Ti HCP nanowires at their tension. The temperature dependence of the Young's modulus is similar to the known experimental results. The obtained simulation results are based not only on the analysis of structural changes in the entire volume, but also in certain areas and the atomic planes in the uniaxial tensile deformation in the direction <0001> Ti nanowires at 10 K. Similar studies were conducted on samples of Ti nanowires of different lengths, peppered section.

Opto-mechano-electrical tripling in ZnO nanowires probed by photocurrent spectroscopy in a high-resolution transmission electron microscope

Photocurrent spectroscopy of individual free-standing ZnO nanowires inside a high-resolution transmission electron microscope (TEM) is reported. By using specially designed optical in situ TEM system capable of scanning tunneling microscopy probing paired with light illumination, opto-mechano-electrical tripling phenomenon in ZnO nanowires is demonstrated. Splitting of photocurrent spectra at around 3.3 eV under in situ TEM bending of ZnO nanowires directly corresponds to nanowire deformation and appearance of expanded and compressed nanowire sides. Theoretical simulation of a bent ZnO nanowire has an excellent agreement with the experimental data. The splitting effect could be explained by a change in the valence band structure of ZnO nanowires due to a lattice strain. The strain-induced splitting provides important clues for future flexible piezo-phototronics.

Strong Hall-Petch Type Behavior in the Elastic Strain Limit of Nanotwinned Gold Nanowires.

Pushing the limits of elastic deformation in nanowires subjected to stress is important for the design and performance of nanoscale devices from elastic strain engineering. Particularly, introducing nanoscale twins has proved effective in rising the tensile strength of metals. However, attaining ideal elastic strains in nanotwinned materials remains challenging, because nonuniform twin sizes locally affect the yielding behavior. Here, using in situ high-resolution transmission electron microscopy tensile testing of nanotwinned [111]-oriented gold nanowires, we report direct lattice-strain measurements that demonstrate a strong Hall-Petch type relationship in the elastic strain limit up to 5.3%, or near the ideal theoretical limit, as the twin size is decreased below 3 nm. It is found that the largest twin in nanowires with irregular twin sizes controls the slip nucleation and yielding processes in pure tension, which is in agreement with earlier atomistic simulations. Continuous hardening behavior without loss of strength or softening is observed in nanotwinned single-crystalline gold nanowires, which differs from the behaviors of bulk nanocrystalline and nanotwinned-nanocrystalline metals. These findings are of practical value for the use of nanotwinned metallic and semiconductor nanowires in strain-engineered functional microdevices.

Influence of Atomic Defect on the Deformation Properties of Nanowires Subjected to Uniaxial Tension

Atomic defects play an important role in the brittle deformation of nanowires at low temperatures. With molecular dynamics simulations, we study the influence of vacancy defects on the deformation and breaking behaviors of [10 oriented single-crystal gold nanowires at 50 and 150 K. The size of the nanowire is 10a × 10a × 30a (a stands for lattice constant, 0.408 nm for gold). It is shown that good crystalline structure appears in the whole deformation process, and it is in a brittle way at low temperature. The nanowire breaking behavior is sensitive to atomic vacancies when the atomic vacancy ratio is 1% in single-layer crystalline plane. Within the limitation of vacancy-induced breaking of the nanowire, the mechanical strengths increase under atomic vacancies. However, it decreases with the defect ratio increasing.

Plasmonic tuning of silver nanowires by laser shock induced lateral compression

Laser shock induced lateral compression has been demonstrated to controllably flatten cylindrical silver nanowires. Nanowires with circular cross-sections of diameter 70 nm are significantly shaped laterally, which transformed them to metallic ribbons of huge width of 290 nm and of thickness down to 13 nm, amounting the aspect ratio to as high as 22, at a laser intensity of 0.30 GW cm(-2). Above the laser intensity of 0.30 GW cm(-2) though, nanowires are observed to be ruptured. Lateral deformations of nanowires are achieved without altering longitudinal dimensions. Selected area electron diffraction patterns on the laterally deformed nanowires reveal that the flattening gives rise to twinning under high strain rate deformation without actually degrading crystallinity. As the 1D nanowire turns into a 2D metallic nanoribbon, new plasmonic modes and their combinations emerge. The transverse plasmon mode does not shift substantially, whereas longitudinal modes and their combinations are greatly influenced by lateral deformation. Apart from the transverse mode, which is dominant in a 1D nanowire and diminishes heavily when lateral deformation occurs, there is a presence of several longitudinal plasmonic modes and their combinations for metallic nanoribbons, which are revealed by experimental extinction spectra and also supported by finite-difference time-domain (FDTD) simulation. Such plasmonic tuning of silver nanowires across the visible range demonstrates the capability of a laser shock induced lateral compression technique for various emerging plasmonic applications. The laser shock compression technique has the advantages of flexibility, selectivity and tunability while retaining crystallinity of metallic nanowires, all of which enable it to be a potential candidate for plasmonic tuning of nanogeometries.

Mechanical Characterization of Co/Cu Multilayered Nanowires

The mechanical deformation properties of (110) Co/Cu multilayered nanowires were studied by Molecular Dynamics under uniaxial tensile and compressive stresses. The potential of the immiscible CoCu system was modeled by a second-moment tight-binding approximation. Stress-strain curves at different conditions were obtained and the elastic modulus and yield stress were analyzed. Both magnitudes are approximately independent of the strain rate, except at high values. They decrease linearly with increasing temperature. Below a volume-to-surface-area ratio, their values drastically increase and diverge from the bulk values. If the thickness of the Cu sublayers increases, the Young's modulus and yield stress decrease, although in a different way. The elastic modulus decreases linearly and the yield stress falls steeply whenever Cu is present in the nanowire, since the lattice distortion takes place firstly and fundamentally in Cu sublayers. The change in the axial stress at the interface is little significant on average and rather localized. Unlike, the transverse stress has a non-uniform distribution along the Cu sublayer, especially at the yield point. The Young's modulus and yield stress are larger in tension than in compression. Under tensile stress, nanowires slip via partial dislocation nucleation and propagation. Unlike, compressive deformation of nanowires takes place via both partial and full dislocations.

Effects of temperature, loading rate and nanowire length on torsional deformation and mechanical properties of aluminium nanowires investigated using molecular dynamics simulation

Single-crystal aluminium nanowires under torsion are studied using molecular dynamics simulations based on the many-body tight-binding potential. The effects of temperature, loading rate and nanowire length are evaluated in terms of atomic trajectories, potential energy, von Mises stress, a centrosymmetry parameter, torque, shear modulus and radial distribution function. Simulation results clearly show that torsional deformation begins at the surface, extends close to the two ends and finally diffuses to the middle part. The critical torsional angle which represents the beginning of plastic deformation varies with different conditions. Before the critical torsional angle is reached, the potential energy and the torque required for the deformation of a nanowire significantly increase with the torsional angle. The critical torsional angle increases with increasing nanowire length and loading rate and decreasing temperature. The torque required for the deformation decreases and the shear modulus increases with increasing nanowire length. For higher temperatures and higher loading rates, torsional buckling more easily occurs at the two ends of a nanowire, whereas it occurs towards the middle part at or below room temperature with lower loading rates. Geometry instability occurs before material instability (buckling) for a long nanowire.

Contributions of the embedded-atom method to materials science and engineering

Abstract