In-situ Electron Microscopy Study On Mechanical Properties In Gan And Si Nanowires

Mechanical properties, as one of the most important physical properties ofmaterials, have been widely studied at macroscale. However, the methodologyand investigations of nano mechanics are still under developing. Since onedimensional semiconductor nano materials are considered as the building blocksfor high-performance nano devices, their mechanical behaviors are critical forthe desining standard of these devices. Meanwhile, the electrical, optical andsome other properties of semiconductor nanowires are able to be tailored by thestress effect. Therefore, the investigations of the mechanical properties of GaNnanowires and Si nanowires, which are the most two important classes ofsemiconductor materials, have been conducted by using the In-situ electronmicroscopy.The GaN nanowires we synthesized can be devided into three categories,which are the single crystalline nanowire, the obtuse-angle twin nanowires andthe acute-angle twin nanowires. The planar defects, such as the twin boundariesand the stacking faults in these GaN nano structures have been characterized byelectron microscopy. By the assistance of molecular dynamic simulations, themodel dealing with two growing mechanisms has been proposed to explain thestructure distribution in our synthesized GaN nanowires.The elastic properties of GaN nanowires with different structure, wereinvestigated by in-situ electron microscopy. The electric-field-inducedresonance method was utilized to reveal that the single crystalline GaNnanowires ranging90.00-110.00nm in diameter along [120] direction have thesimilar Young’s modulus as the bulk value300GPa. However, an entirelydifferent elastic behavior of the obtuse-angle twin GaN nanowires is disclosedboth by the in-situ SEM resonance technique and in-situ TEM tensile tests. It isindicated by this study that this dramatic decrease of Young’s modulus isattributed to the numbers and relative orientations of (001) stacking faults inobtuse-angle twin GaN nanowires. The rules of mixture in classical mechanicsare still work to quantitatively explain our experimental results of themechanical properties. Moreover, the elastic-plastic transition in Si nanowires has beeninvestigated. Two in-situ TEM experiments were conducted to study theelectron-beam effect on the plasticity of Si nanowires. An e-beam illuminatingwith a current intensity of3.20A/cm2would result in the bond re-formingprocess and achieve the plastic deformation with a bent strain over40%in SiNWs near the room temperature. In addition, an effective method was proposedto shape the Si NWs, where an e-beam-induced elastic-plastic transition tookplace.