In situ deformation transmission electron microscopy investigation of the mechanical behaviours of nanomaterials

Abstract

Due to their superior properties, nanomaterials (NMs) have many significant applications. The mechanical properties of NMs including nanowires (NWs) and nanofilms are a crucial factor in designing devices where predictable and reproducible operation is important. However, due to the difficulty of mechanical testing at nanoscale, mechanical properties of NMs have not been as extensively investigated. This thesis aims to apply an in situ deformation transmission electron microscopy (TEM) technique combined with finite element analysis (FEA) to investigate the mechanical behaviours of NMs. The first chapter of this thesis presents a summary of the applications, synthesis methods, nanomechanical characterisation techniques, and mechanical behaviours of nanomaterials. The second chapter provides a general description of the methods used in this thesis. Details of the experimental and modelling procedures are also described. In the third chapter, quantitative investigation of the effects of loading misalignment and tapering of NWs on the measured compression and tensile mechanical properties is presented. In the fourth chapter, the Young’s moduli of GaAs NWs with two distinct structures – defect-free single crystalline wurtzite and wurtzite containing a high density of stacking faults (SFs) – are measured. The presence of a high density of SFs was found to increase the Young’s modulus by 12%. Determination of the elastic modulus of NMs with sizes of a few nanometres is a significant challenge. In the fifth chapter, a method combining in situ compression TEM and FEA is developed to measure the Young’s modulus of nanoscale films with thicknesses down to ~ 2 nm by using a core–shell NW structure. Major conclusions are drawn from this PhD research in the last chapter. Some possible future work is proposed as extension of what has been achieved.