Center for Functional Nanomaterials Seminar

It is often a challenge to measure accurately the mechanical properties of nanostructures and nanomaterials on account of their extremely small physical dimensions. Recently, we have developed an in situ TEM nanomechanical testing apparatus which enable to acquire quantitative mechanical data while simultaneously recording the microstructural evolution of the materials during the deformation tests. A one-to-one relationship between an imposed stress and an individual deformation event can be made through the time. In this talk, our recent progress in the application of this in situ TEM device for measuring the mechanical behavior of individual single crystal nickel pillars and nanocrystalline CdS hollow spheres will be reported. Prior to the deformation tests, nickel pillars fabricated with Focused Ion Beam (FIB) were observed to contain a high density of defects. However, quite unexpectedly, the dislocation density was observed to decrease dramatically during the deformation process and, in some cases, even resulted in a dislocation-free crystal. The phenomena, which we termed as "mechanical annealing", are direct confirmation of dislocation starvation mechanism and sheds new light on the unusual mechanical properties associated with submicron- and nano- scale structures. The compression tests on nanocrystalline CdS hollow spheres revealed that as prepared structure can withstand theoretical level high stress while at the same time enables the spherical shells to be compressed up to 20% of the outer diameter of the spheres prior to fracture. These findings shed new lights on the potential applications of nanostructured materials.