CarParrinello Molecular Dynamics Simulations of Tensile Tests on Si⟨ 001⟩ Nanowires (original) (raw)
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a b s t r a c t Molecular dynamics (MD) simulations were carried out to study bulk silica glass and amorphous silica nanowire under uniaxial tension. Periodic boundary conditions were employed to mimic infinite bulk samples. Cutting and casting methods were used to prepare nanowires. Our study shows that simulation parameters, such as system size, cooling rate, working temperature and strain rate, need to be carefully chosen in order to correctly reproduce the brittle fracture behavior of amorphous silica. The stiffness of silica glass is less sensitive to these parameters than the tensile strength and the failure strain. However, the sample density and the anomalous nonlinear elasticity of silica glass should be correctly taken into account to get an accurate estimate of its stiffness from MD simulations. Our study also shows that, with proper simulation parameters, amorphous silica nanowires down to 1 nm in radius still exhibits a brittle fracture behavior. Nanowires prepared by the cutting method have a lower stiffness and tensile strength but a higher failure strain than the cast ones, due to more surface defects generated during the cutting process at low temperatures. Defects-induced ductility could be an effective way to make less brittle nanostructures of amorphous silica.
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Deformation and fracture mechanisms of ultrathin Si nanowires (NWs), with diameters of down to ∼9 nm, under uniaxial tension and bending were investigated by using in situ transmission electron microscopy and molecular dynamics simulations. It was revealed that the mechanical behavior of Si NWs had been closely related to the wire diameter, loading conditions, and stress states. Under tension, Si NWs deformed elastically until abrupt brittle fracture. The tensile strength showed a clear size dependence, and the greatest strength was up to 11.3 GPa. In contrast, under bending, the Si NWs demonstrated considerable plasticity. Under a bending strain of <14%, they could repeatedly be bent without cracking along with a crystalline-to-amorphous phase transition. Under a larger strain of >20%, the cracks nucleated on the tensed side and propagated from the wire surface, whereas on the compressed side a plastic deformation took place because of dislocation activities and an amorphous transition.
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International Journal of Nanotechnology, 2004
In the present work we have reviewed the importance of conductance histograms as an experimental tool able to address the statistical behaviour of the electronic transport through metallic nanowires. We have described how molecular dynamics techniques combined with embedded-atom method (EAM) are able to reproduce the general features noticed during metallic nanowire breaking experiments. We have studied the effect of temperature on the minimum cross-section histograms. Our results show that the breaking dynamics is strongly temperature dependent, giving rise to remarkable changes in the computed histograms. We found, for Gold, that conductance and configuration histograms are not correlated, thus indicating that experimental conductance peaks are due to actual quantized conductance effects. For Aluminum, the situation is different, since we found a strong correspondence between our minimum cross-section histograms and the experimental conductance histograms, indicating the relevant role of atomic configurations. We have addressed the study of the stretching of thick Au and Al nanocontacts, finding that there is evidence of the formation of preferred atomic configurations. The electronic origin of such stable atomic arrangements has been discarded, and a plausible explanation has been given in terms of the completion of ionic shells or subshells. Gold and Aluminum nanowires present at room temperature a similar character to that found for alkali wires at low temperatures.
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Silicon (Si) has been recognized as a promising anode material for the next-generation high-capacity lithium (Li)-ion batteries because of its high theoretical energy density. Recent in situ transmission electron microscopy (TEM) revealed that the electrochemical lithiation of crystalline Si nanowires (c-SiNWs) proceeds by the migration of the interface between the lithiated Si (LixSi) shell and the pristine unlithiated core, accompanied by solid-state amorphization. The underlying atomic mechanisms of Li insertion into c-Si remain poorly understood. Herein, we perform molecular dynamics (MD) simulations using the reactive force field (ReaxFF) to characterize the lithiation process of c-SiNWs. Our calculations show that ReaxFF can accurately reproduce the energy barriers of Li migration from DFT calculations in both crystalline (c-Si) and amorphous Si (a-Si). The ReaxFF-based MD simulations reveal that Li insertion into interlayer spacing between two adjacent (111) planes results in...
TWASP, 2022
An extensive study of mechanical properties on the Copper nanowire is conducted in this paper. A threepoint bending method, based on AFM bending experiment, has employed in order to obtain mechanical properties of Cu NWs. Tensile test by means of strain rate is a well-known method to evaluate mechanical properties in Molecular Dynamics (MD) simulations. A comparisional analysis between young's modulus gain through tensile test and bending test, employed in this paper, has shown that mechanical strength is slightly more in axial loading than lateral loading direction. Also, study on different loading rate is done here to evaluate which loading rate should be indicated as impact load rather than bending load. For any nanomaterial, their superior mechanical properties are evident due to their large surface-to-volume ratio. In this paper to evaluate this phenomenon, a study of bending effect on various Cu NWs depth has shown that with the decrement of depth of the material, and so by increasing surface-tovolume ratio, mechanical properties of the material increases. Additionally, an effect of various indenter size is studied to gain insight on its effect on mechanical properties of Cu NWs.
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Journal of Applied Physics, 2015
This study investigates the structural transformations and properties of silica glass nanowires under tensile loading via molecular dynamics simulations using the BKS (Beest-Kramer-Santen) interatomic potential. Surface states of the elongated nanowires were quantified using radial density distributions, while structural transformations were evaluated via ring size distribution analysis. The radial density distributions indicate that the surface states of these silica nanowires are significantly different than those of their interior. Ring size analysis shows that the ring size distributions remain mainly unchanged within the elastic region during tensile deformation, however they vary drastically beyond the onset of plastic behavior and reach plateaus when the nanowires break. The silica nanowires undergo structural changes which correlate with strain energy and ring size distribution variations. It is also found that the ring size distribution (and strain energy) variations are dependent on the diameter of the silica nanowires. Interestingly, for ultrathin nanowires (diameters < 5 .0 nm), the variation of ring size distributions shows a distinct trend with respect to tensile strain, indicating that the surface states play a key role in both modifying the mechanical properties and structural characteristics. These results for ultrathin nanowires are consistent with prior theoretical and simulation predictions. The overall findings in this study provide key insights into the novel properties of nano-sized amorphous materials, and are aimed to inspire further experiments. V