In situ experimental mechanics of nanomaterials at the atomic scale

Abstract

Sub-micron and nanostructured materials exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. These properties are important for their applications as building blocks for the fabrication of nano- and micro-devices as well as for their use as components for composite materials, high-strength structural and novel functional materials. These nano-related deformation and mechanical behaviors, which are derived from possible size and dimensional effects and the low density of defects, are considerably different from their conventional bulk counterparts. The atomic-scale understanding of the microstructural evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials, novel structures and applications. This review presents the recent developments in the methods, techniques, instrumentation and scientific progress for atomic-scale in situ deformation dynamics on nanomaterials, including nanowires, nanotubes, nanocrystals, nanofilms and polycrystalline nanomaterials. The unusual dislocation initiation, partial-full dislocation transition, crystalline–amorphous transitions and fracture phenomena related to the experimental mechanics of the nanomaterials are reviewed. Current limitations and future aspects using in situ high-resolution transmission electron microscopy of nanomaterials are also discussed. A new research field of in situ experimental mechanics at the atomic scale is thus expected. The properties of a material depend not only on its composition but also on the exact arrangement of its atoms. In particular, nanostructured materials such as nanotubes, nanocrystals or polycrystalline materials are much stronger and more elastic than their bulk counterparts and exhibit different plastic deformations, making them suitable for a variety of applications. Lihua Wang and co-workers review how recent developments in transmission electron microscopy (TEM) techniques enable materials scientists to characterize, at the atomic scale, both the chemical composition of a nanomaterial and its deformation dynamics under stress and strain, in situ, and in real time. Some possible pitfalls and challenges remain — for example, over-irradiation with the TEM electron beam may damage the sample studied, and observations must typically be carried out under vacuum — but such detailed characterization provides a good understanding of the mechanisms at play. It therefore holds promise for the control of the mechanical, but also chemical and physical, properties of nanostructured materials through the application of stress or strain. Nanostructured materials always exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. The atomic-scale understanding of the microstructure evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials and applications. In situ transmission electron microscopy (TEM) experiments provide the possibility for direct observation of the deformation mechanisms at the atomic scale. This review presents the recent developments of techniques and scientific progress for the atomic-scale in situ TEM deformation dynamics on nanomaterials. Current limitations and future aspects are also discussed.