Abnormal elastic modulus behavior in a crystalline–amorphous core–shell nanowire system

Abstract

We investigated the elastic modulus behavior of crystalline InAs/amorphous Al2O3 core-shell heterostructured nanowires with shell thicknesses varying between 10 and 90 nm by conducting in situ tensile tests inside a transmission electron microscope (TEM). Counterintuitively, the elastic modulus behaviors of InAs/Al2O3 core-shell nanowires differ greatly from those of bulk-scale composite materials, free from size effects. According to our results, the elastic modulus of InAs/Al2O3 core-shell nanowires increases, peaking at a shell thickness of 40 nm, and then decreases in the range of 50-90 nm. This abnormal behavior is attributed to the continuous decrease in the elastic modulus of the Al2O3 shell as the thickness increases, which is caused by changes in the atomic/electronic structure during the atomic layer deposition process and the relaxation of residual stress/strain in the shell transferred from the interfacial mismatch between the core and shell materials. A novel method for estimating the elastic modulus of the shell in a heterostructured core-shell system was suggested by considering these two effects, and the predictions from the suggested method coincided well with the experimental results. We also found that the former and latter effects account for 89% and 11% of the change in the elastic modulus of the shell. This study provides new insight by showing that the size dependency, which is caused by the inhomogeneity of the atomic/electronic structure and the residual stress/strain, must be considered to evaluate the mechanical properties of heterostructured nanowires.

Elastic Behavior of Nb2O5/Al2O3 Core–Shell Nanowires in Terms of Short-Range-Order Structures

“…Furthermore, the determined moduli have been found constant irrespective for the applied external load. A similar trend was also observed by Lee et al., who reported a slight increase in E shell at a shell thickness of about 40 nm followed by a drastic drop in E shell for larger shell thickness down to about 100 GPa for shell thicknesses between 50 and 90 nm …”

“…As the experimental results in Figure a indicate, further investigation needs to be conducted, namely, an estimation of the effective Young’s modulus by finding the most suitable physical parameter for the Al 2 O 3 modulus. As discussed previously, Lee et al investigated InAs/Al 2 O 3 core–shell NWs and reported a change in the Young’s modulus of the Al 2 O 3 shell, E s , with thickness and determined that the Young’s modulus of the core, E c , did not vary with the diameter . Thus, a similar approach is assumed to be applied to the Nb 2 O 5 /Al 2 O 3 core–shell NWs in this work.…”

Tunable Mechanical Property and Structural Transition of Silicon Nitride Nanowires Induced by Focused Ion Beam Irradiation

“…Silicon nitride (Si 3 N 4 ) is a widely applied semiconductor in electronic devices, integrated photonic devices, and micrometer/nanometer-scale electromechanical systems. − As a traditional covalent ceramic, it possesses many intriguing properties, such as high strength, high hardness, high modulus, and high dielectric coefficient. , In the nanoscale form, Si 3 N 4 as a reinforced whisker can be used for the fabrication of the composite materials. , To further modify its mechanical properties, ion beam irradiation-induced composite structure represents one of the main strategies for material design and fabrication. − Till now, many experimental studies of the mechanical properties of Si 3 N 4 NWs have been reported. − Theoretically, failure mechanisms of Si 3 N 4 NW and mechanical properties of the core–shell materials have also investigated. − However, due to the technical difficulties in deformation test by in situ electron microscopy, the tensile behavior of Si 3 N 4 NWs has not yet been evaluated, which hinders further elucidation of the deformation mechanisms of the nanoscale building blocks.…”

Formation of arsenic clusters in InAs nanowires with an Al2O3 shell

“…The microstructural properties of InAs NWs adopted in our experiments were described in detail in our previous study. 17 Based on the analyses of the selected area electron diffraction patterns and the results of the fast Fourier transform of HRTEM images, it was conrmed that the Al 2 O 3 thin shells were amorphous. The diameter of InAs NWs was in the range of several tens to several hundreds of nanometers, and it was also conrmed that InAs NWs were fully covered by the Al 2 O 3 shells.…”

“…The detailed ALD processes for Al 2 O 3 shells have been described elsewhere. 17 After the ALD process, the grid and heating device were placed on TEM holders for microstructural characterization and in situ heating TEM experiments. The in situ TEM experiments were conducted using a field-emission gun (FEG) transmission electron microscope operating at an accelerating voltage of 300 kV (FEI Tecnai F30 S-Twin, USA).…”