Breaking Of Nanowires Research Articles

Strengthened and toughened SiHfBCN-based high-temperature resistant adhesive with SiC NWs

To further improve the performance of binders, a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics (PDC) route using TiB2, Polysiloxane (PSO) and short SiC nanowires as fillers. The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature, as well as the reinforcing mechanism was studied. Compared with the adhesive without SiC nanowires, after curing (at 170 °C) and pyrolysis (at 1000 °C) in air, the appropriate adding of SiC nanowires upgrades the room temperature and high temperature (at 1000 °C in air) adhesive strength to (12.50 ± 0.67) MPa (up by about 32%) and (13.11 ± 0.79) MPa (up by about 106%), respectively. Attractively, under the synergistic impact of the nanowire bridging, nanowire breaking, nanowire drawing and crack deflection, the optimized adhesive exhibits multi-stage fracture, causing the increscent fracture displacement.

A route for the top-down fabrication of ordered ultrathin GaN nanowires

We introduce a facile route for the top-down fabrication of ordered arrays of GaN nanowires with aspect ratios exceeding 10 and diameters below 20 nm. Highly uniform thin GaN nanowires are first obtained by lithographic patterning a bilayer Ni/SiN x hard mask, followed by a combination of dry and wet etching in KOH. The SiN x is found to work as an etch stop during wet etching, which eases reproducibility. Arrays with nanowire diameters down to (33 ± 5) nm can be achieved with a uniformity suitable for photonic applications. Next, a scheme for digital etching is demonstrated to further reduce the nanowire diameter down to 5 nm. However, nanowire breaking or bundling is observed for diameters below ≈20 nm, an effect that is associated to capillary forces acting on the nanowires during sample drying in air. Explicit calculations of the nanowire buckling states under capillary forces indicate that nanowire breaking is favored by the incomplete wetting of water on the substrate surface during drying. The observation of intense nanowire photoluminescence at room-temperature indicates good compatibility of the fabrication route with optoelectronic applications. The process can be principally applied to any GaN/SiN x nanostructures and allows regrowth after removal of the SiN x mask.

Selective breaking and re-joining of CuO nanowires by nanosecond laser irradiation

Nanostructures incorporating copper oxide (CuO), a narrow bandgap p-type semiconductor, are well suited for applications such as gas/biosensors, field emission devices, and photodetectors. However, the use of CuO nanocomponents in these applications is currently limited by the availability of fabrication and in situ processing techniques. In this paper, we show that the electrical and mechanical properties of CuO nanowire (NW) networks can be adjusted through sequential processing with nanosecond laser radiation. This new two-stage process involves selective breakage/cleaving of CuO NWs with an initial set of laser pulses, followed by irradiation with a second set of laser pulses applied in an optimized orientation to tailor bonding and junction formation between pairs and bundles of previously separated CuO NWs. We find that stage one processing introduces a high concentration of oxygen vacancies in NWs leading to the nucleation of dislocations and high strain. This localized strain is responsible for the breaking of individual NWs, while the high oxygen vacancy concentration modifies the electrical conductivity within each NW. The second stage involves re-orientation of the laser beam, followed by additional laser irradiation of the NW network. This has been found to result in the bonding of NWs and the creation of junctions in regions where CuO NWs are in contact. Laser-induced heating under these conditions produces melting in the contact areas between NWs and is accompanied by the reduction of CuO to form Cu2O as verified via XPS and Raman analysis. XRD and TEM observations demonstrate that plastic deformation within CuO NWs dominates in stage one laser processing. The enhancement of electrical conductivity observed, following stage two processing, is attributed due to an increase in the concentration of laser-induced oxygen vacancies as well as the formation of localized bridging and junction sites in the overall NW network.

Local Heat Dissipation of Ag Nanowire Networks Examined with Scanning Thermal Microscopy

Silver nanowires (AgNWs) have shown remarkable potential as materials for transparent conductive electrodes in next-generation flexible devices because of their excellent physical properties. However, despite this advantage, breakdown occurs when AgNWs are exposed to a high temperature and current flow, which has been a significant obstacle. Therefore, a thorough understanding of the breakdown based on local thermal and electrical analyses is essential for developing new devices for various electronic applications. As it is difficult to measure the local heat dissipation occurring at a nanoscale, the breakdown process has not yet been analyzed in detail through an experimental approach. In this study, the local breakdown process due to Joule heat and concentrated current density was examined using scanning thermal microscopy when current flowed through a AgNW network. The results showed that the nanowire breaks at ∼453 K, which is lower than the previously reported temperature of breakdown that occurred only via environmental heating. In this study, we found that the AgNW network can be broken down at temperatures below ∼500 K because the atomic flux due to the combined effects of Rayleigh instability and electromigration is applied to atoms on the surface when the nanowires operate electrically. This work proposes that electromigration and Rayleigh instability should be considered in the design of AgNW devices.

Structural evolution and the role of native defects in subnanometer MoS nanowires

We carried out first-principles calculations based on density functional theory aiming to understand the structural evolution along the stretching process and the impact of native defects in metallic subnanometer MoS nanowires (NWs). By pulling the pristine NWs quasistatically, we investigate the full structural evolution along the stretching process until the nanowire breaking point, obtaining a maximum applied stress (force) of $\ensuremath{\approx}18.9$ GPa (7.1 nN). On the other hand, since the existence of intrinsic defects is likely to occur in these samples, we show that under S-rich conditions a sulfur antisite is found to be the energetically most stable defect, and under Mo-rich conditions a sulfur vacancy has the lowest formation energy. Our results also reveal that these defects present local reconstruction that can be clearly identified by the simulated scanning tunneling microscopy images. Furthermore, through a detailed analysis of the electronic structure, we verify that with the exception of the Mo interstitial and S antisite, all defects preserve the metallic behavior of the MoS nanowires.

Selective Wet Etching of Silicon Germanium in Composite Vertical Nanowires.

Silicon germanium (SixGe1-x or SiGe) is an important semiconductor material for the fabrication of nanowire-based gate-all-around transistors in the next-generation logic and memory devices. During the fabrication process, SiGe can be used either as a sacrificial layer to form suspended horizontal Si nanowires or, because of its higher carrier mobility, as a possible channel material that replaces Si in both horizontal and vertical nanowires. In both cases, there is a pressing need to understand and develop nanoscale etching processes that enable controlled and selective removal of SiGe with respect to Si. Here, we developed and tested solution-based selective etching processes for SiGe in composite (SiNx/Si0.75Ge0.25/Si) vertical nanowires. The etching solutions were formed by mixing acetic acid (CH3COOH), hydrogen peroxide (H2O2), and hydrofluoric acid (HF). Here, CH3COOH and H2O2react to form highly oxidizing peracetic acid (PAA orCH3 CO3H). The hydrofluoric acid serves both as a catalyst for PAA formation and as an etchant for oxidized SiGe. Our study shows that an increase in anyofthe two oxidizer(H2O2 and PAA)concentrations increases the etch rate, and the fastest etch rate of SiGe is associated with the highest PAA concentration. Moreover, using in situ liquid-phase TEM imaging, we tested the stability of nanowires during wet etching and identified the SiGe/Si interfaceto be the weakest plane; we found that once the diameter of the 160-nm-tall Si0.75Ge0.25 nanowire reaches ∼15 nm during the etching, the nanowire breaks at or very close to this interface. Our study provides important insight into the details of the nanoscale wet etching of SiGe and some of the associated failure modes that are becoming extremely relevant for the fabrication processes as the size of the transistors shrink with every new device generation.

Highly Conducting Hybrid Silver-Nanowire-Embedded Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) for High-Efficiency Planar Silicon/Organic Heterojunction Solar Cells.

Embedding nanowires, such as silver nanowires (AgNWs), in a transparent conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to enhance its conductivity is technologically important for improving the performances of devices comprising transparent conductive layers. Addition of nanowires in the highly conducting form of cosolvent (ethylene glycol) or mixed-cosolvent (ethylene glycol and methanol) modified PEDOT:PSS could change the nanowire structure and significantly alter the conductivity. Here, we report a simple method to embed AgNWs in PEDOT:PSS efficiently to improve its conductivity. By incorporating nanowires in the mixed cosolvent matrix prior to addition into PEDOT:PSS, this method preserves the structure of the nanowires while enabling conductivity enhancement. In contrast, the addition of AgNWs into cosolvent-premodified PEDOT:PSS leads to breaking of nanowires and conductivity impediment. The hybrid films with efficiently embedded AgNWs and mixed-cosolvent-modified PEDOT:PSS show a sheet resistance of 104 Ω/□, which is among the lowest ever reported for the as-deposited films, with conductivity enhancement of 33% relative to that of mixed-cosolvent-modified PEDOT:PSS. The resulting planar heterojunction solar cell (HSC) based on AgNW-embedded PEDOT:PSS exhibits a power conversion efficiency of greater than 15%. This demonstrates the importance of reducing sheet resistance by integrating nanowires into the PEDOT:PSS matrix as effective charge-transfer conduits interconnecting the highly conducting quinoid chains. The present approach to efficiently embed AgNWs in PEDOT:PSS could be readily extended to other nanowires or nanoparticles for improving the performance of PEDOT:PSS for applications in not just HSCs but indeed other electronic devices that require both transparent and highly conductive layers.

Deformation and Fracture of Metallic Nanowires

A many-body interatomic potential for metallic nanowires within the second-moment approximation of the tight-binding model (the Cleri-Rosato potential) was employed to carry out three dimensional molecular dynamics simulations. Molecular dynamics simulation results for metallic nanowires at various temperature are presented. The stress–time and stress length curves for nanowires are simulated. The breaking and yield stress of nanowires are dependent on the Volume and temperature. The necking, Plastic deformation, slipping domain, twins, clusters, microspores and break-up phenomena of nanowire are demonstrated. Stress decreases with increasing nanowire volume and temperature. The final breaking position occurs at the central part of the nanowire when it is short, as the nanowire length increases the breaking position gradually shifts to the ends.

Thermal stability and spontaneous breakdown of free-standing metal nanowires

We present a model for vacancy-mediated spontaneous breakdown of free-standing monatomic nanowire based on exclusively random, thermally activated motion of atoms. The model suggests a new two-step vacancy-mediated mechanism for nanowire rupture compared to the more complex three-step hole-mediated mechanism driving the disintegration of nanowire on crystalline surface. It also demonstrates that a free-standing nanowire breaks down much more rapidly than a nanowire on a substrate, because it cannot experience the stabilizing effect of the nanowire/substrate interactions. The rupture mechanism includes single atomic vacancy generation, preceded by appearance of weakly bonded active atoms. The analysis of the simulation data indicates that the active atoms act as a precursor of vacancy formation. These two successive events in the temporal evolution of the nanowire morphology bring the free-standing nanowire into irreversible unstable state, leading to its total disintegration.The present study also manifests an unexpected substantial increase of the nanowire lifetime with diminishing the strength of the atomic interactions between the nanowire atoms. The simulation data reveal three energy regions where a large oscillatory variation of nanowire lifetime is realized. The first region of strong atomic interactions is characterized by tight nanowire rigidity and short lifetime. The next, second region in the consecutive step-down of the attractive interatomic force is characterized by generation of wave-shaped morphology of the atomic chain, enhanced flexibility and dramatic increase of nanowire lifetime. In the last, third region, further weakening of the interactions returns the nanowire again to unstable, short-lifetime state. The observed phenomenon is considered as a “stick-like” to “polymer-like” transition in the nanowire atomic structure as a result of interaction energy variation. The enhanced flexibility reduces the nanowire free energy since it favors and facilitates the rate of entropy propagation in the atomic chain structure. The observed phenomenon opens a way for a new type atomic scale control on the thermal stability of both free-standing nanowire and nanowire on crystalline substrate. The present study also extends the validity of the three-step breakdown mechanism of nanowire on crystalline substrate to the specific case of thermally activated free-standing nanowire rupture not affected by any external forces.

Monte Carlo simulation of elongating metallic nanowires in the presence of surfactants.

Nanowires of different metals undergoing elongation were studied by means of canonical Monte Carlo simulations and the embedded atom method representing the interatomic potentials. The presence of a surfactant medium was emulated by the introduction of an additional stabilization energy, represented by a parameter Q. Several values of the parameter Q and temperatures were analyzed. In general, it was observed for all studied metals that, as Q increases, there is a greater elongation before the nanowire breaks. In the case of silver, linear monatomic chains several atoms long formed at intermediate values of Q and low temperatures. Similar observations were made for the case of silver-gold alloys when the medium interacted selectively with Ag.

Monatomic metal nanowires: Rupture kinetics and mean lifetime

We present a model for the kinetics of spontaneous (unforced) rupture of monatomically thick metal nanowire on atomically smooth crystal face. The nanowire breaks down spontaneously solely because of the thermal motion of the atoms in it and the underlying crystal. Our model describes the nanowire rupture as a three-step process involving (i) appearance of atoms active in vacating their positions, (ii) generation of atomic vacancies, and (iii) formation of holes (vacancy dimers) in the nanowire. The model is based on Monte Carlo simulation results for the temporal evolution of initially straight monatomic chain of Cu atoms on Cu(111) crystal face. The simulation provides data for the time dependence of the number Nv of vacancies and the number Nh of holes in the nanowire, as well as for the probabilities Pv and Ph to form, respectively, at least one vacancy and at least one hole until time t. We describe the nanowire rupture kinetics by using rate equations and obtain expressions for the nanowire mean lifetime and the Nv(t), Nh(t), Pv(t), and Ph(t) dependences. These expressions are found to conform well to the simulation data, which implies a Poissonian random appearance of the first few vacancies and holes in the nanowire.

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.

Reliability of Sensors Based on Nanowire Networks Operating in a Dynamic Environment

Recent advances in nanotechnology have provided the opportunity to significantly enhance the performance of hydrogen gas nanosensors. Our research focuses on the reliability of one particular nanosensor, a network of ultra small palladium nanowires, which detects hydrogen gas through a change in resistivity. The discrete random variable, representing the lifetime of the nanosensor, is defined as the number of exposures to, or cycles of, hydrogen gas that the nanosensor can withstand before it no longer functions. The nanosensor is modeled, and the reliability is analyzed under the assumption that the nanosensor is performing in an environment where the probability of a nanowire breaking changes after each cycle of hydrogen gas. Nanoscale components present unique difficulties when evaluating the reliability of any device. We attempt to resolve some of these issues by creating a flexible model that allows for the unknown characteristics of the nanosensor to be accounted for. Although this work is motivated by one particular nanosensor, our results can also be applied to assess the reliability of any nanodevice where our proposed model is a reasonable choice.

Thermal Rupture of Monatomic Metal Nanowires

The present study deals with the problem of thermal stability and rupture of metal nanowires, considered here as a monatomic chain located on an atomically smooth crystalline substrate. Based on a recently developed Monte Carlo computational model, the simulation results reveal a scenario of nanowire breaking via formation of atomic vacancies. Depending on temperature, the fluctuations in the positions of the nanowire atoms generate wave-shaped nanowire configurations with specific active sites for breaking. This process is followed by formation of one-atom vacancies in the nanowire. Their overgrowth into vacancies of two, three and more atoms leads to permanent nanowire rupture and, hence, to loss of the nanowire electronic and other physical properties. The time evolution of the atomic-scale nanowire morphology and breaking mechanism are discussed in detail. The proposed model of nanowire rupture sheds light on the general problem of thermal stability of artificial atomic structures on crystal surfaces and their application to electronic and other devices with exotic physical features.

Investigation on the effect of atomic defects on the breaking behaviors of gold nanowires

The mechanical properties and breaking behaviors of the [100]-oriented single-crystal gold nanowires containing a set of defect ratios have been studied at different temperatures using molecular dynamics simulations. The size of the nanowire is 10a × 10a × 30a (a stands for lattice constant, 0.408 nm for gold). The mechanical strengths of the nanowires decrease with the increasing temperature. However, the defects that enhance the local thermal energy have improved the nanowire mechanical strength under a wide range of temperature. Comparing to the single-crystal nanowire, the existence of the atomic defects extends the elastic deformation showing a larger yield strain. By summarizing 300 samples at each temperature, the statistical breaking position distribution shows that the nanowire breaking behavior is sensitive to the atomic defects when the defect ratio is 5 % at 100 K, whereas the ratio is 1 % when temperatures are 300 and 500 K.

In-Situ Mechanical Characterization of Fe3O4 Nanowires

The in-situ mechanical properties of Fe3O4 nanowires (NWs) of a magnetic material grown by an oxide assisted vapor-solid processes are experimentally investigated. Investigations are carried out with a nano-tensile testing technique via a custom-made nanomanipulator inside the SEM. The modulus of elasticity, yield stress and fracture stress of Fe3O4 NWs are estimated to be 23.8 +/- 3.8 GPa, 428 +/- 55 MPa and 1.10 +/- 0.29 GPa, respectively. Strain range at breaking of NWs is obtained as 5% to 11%. The results indicate that the Fe3O4 NWs have highly malleable and stretching properties.

Uniaxial tensile behavior of a bicrystal copper nanowire: Structural characterization with a Fourier transformation method

Abstract Molecular dynamics simulations have been used to investigate the uniaxial tensile behavior of the [1 1 0]‖[1 0 0] bicrystal copper nanowire. Due to the effect of grain boundary, the bicrystal nanowire breaks at the interface with strain increasing, showing a unique brittle feature. In order to well understand the crystallographic characters, we have developed a discrete Fourier transformation technique to analyze the periodic crystal structure. In particular, the atomic density distribution along the long axis of the nanowire is transformed into a frequency–amplitude relationship or into a normalized atomic density distribution. These two treatments enable us to further study the crystal grain orientation and the crystal structure in the stretching process. The frequency–amplitude analysis provides information about the large-scale crystallographic features while the local characteristics are mainly determined by the normalized atomic density distribution. From analyses of the simulation data, we have found that [1 1 0]‖[1 0 0] keeps good crystalline structure until breaking.

An atomistic simulation of structure and thermal stability of［110］Au nanowire during continuous heating

We have used molecular dynamics method with quantum corrected Sutton-Chen type many-body potentials to study the structure and thermal stability of［110］ Au nanowires, and investigate its melting mechanism and shape evolution by introducing the Lindemann index and the minimum radius. The results show that the transformation from fcc to hcp structure occurs in local regions of nanowire before premelting. The melting starts from surface and evolves into interior region, resulting in the overall melting of the nanowire. Subsequently, the neck occurs and induces the final breaking of nanowire into a spherical cluster.

Mechanical and electrical properties of stretched clean and H-contaminated Pd-nanowires

We analyze theoretically the formation of stretched Pd-nanowires and their interactionwith hydrogen. In our approach, we simulate the nanowire stretching process using afirst-principles molecular-dynamics method to obtain realistic atomic geometries of thecontact in its final stages before the nanowire breaks. The electrical conductance of thenanowire is also calculated at each point of the deformation path. For the cleanPd-nanowire in the last stages of the deformation process we find that the nanowiredevelops, first, a one-atom-neck and, at the end, a dimer whose bond is finally broken. Forthese atomic configurations, the calculated electrical conductances are in good agreementwith the experimental evidence. The interaction with hydrogen is analyzed adsorbing oneor two H atoms on the Pd-nanowire for different configurations along the stretchingprocess. In the case of one H atom we obtain geometries with conductances in the range0.8–1.4G0, while for two H atoms we find conductance plateaus with values∼0.5G0 and∼1.0G0.These results are in excellent agreement with the experimental evidence for nanocontact breaking inan H2 atmosphere and indicate that the conductance peak around0.5G0 observed experimentally is associated with nanowires where two H atoms have beenadsorbed.

Phonon spectra in ultrathin gold nanowire under stretching

In recent years, the phonon spectrum has attracted much interest in investigations of electric transfer in nanowires. In this study, molecular dynamics is employed to calculate the phonon characteristics of thinness for 7-1 gold nanowire stretched at room temperature. This study finds that the two major peaks of phonon density of state (DOS) of 7-1 nanowire represent low characteristic frequency shifts to the left, while high characteristic frequency is less significant changed compared with the characteristic frequency in bulk. The high frequency intensity of DOS for 7-1 nanowire is lower than that of low frequency. The low frequency shifts left for large elastic strain during elastic deformation. Moreover, the phonon spectrums of one-atom chain structures formed before the nanowire breaks becomes discrete. The influences of local atomic arrangement and stretch condition on the phonon profile are analyzed in this study.