In Situ Multi-field Loading Experimental Study Inside HRTEM

In this dissertation, combining multi-field loading and in situ TEM observation, we investigated several new thermo-electrical-mechanical behaviors of the materials with different dimensions. The main results are as follows:Combining ex-situ and in situ methods, mechanical behaviors of bulk FCC materials were studied. Nanoscal finger-like structures were observed on the fracture surface of bulk Ag matierials. This nanostructures can be fabricated by pulling bulk silver wires at room temperature using a pair of cutter and pliers. The uniformity of diameter along the length can be attributed to the strain hardening induced by source-limited dislocation starvation, which is also confirmed by the discrete dislocation dynamics simulations. Theoretical estimation of the diameter based on the extended form of Orwon stress agrees with the experimental observation. The length of the nanostructure can be well explained by the mechanism of Rayleigh instability. In situ bending and indentation texting on this nanostructure were conducted inside the TEM. We observed recrystallization and twinning behaviors during the deformation of this nanostructures at room temperature.In situ straining in nanocrystalline Au thin films reveals a new fracture mechanism, i.e. crack propagation via atomic migration. The crack propagates by repetitively nucleating and moving atomic steps from the tip region to the crack rear. The stress concentration at the tip helps in the step nucleation process. The elastic energy density at the notch root decreases with increase of the notch angle, which implies cracks with small angles can propagate along GB more easily.The grain orientation with respect to the grain boundaries (GB) determines the crack blunting and the propagation direction. Under certain circumstances, the crack grows into the grain interior, which is different from the well-known inter-granular fracture in nanocrystalline metals.In situ TEM tensile testing. shows that the deformation mechanisms in sub-10-nm-sized gold ribbons strongly depend on the orientation. The formation of the full dislocation and slip are favored in<001>-oriented nano-junction. However, in the<110>-oriented nano-junction under tension, deformation was dominated by mechanical twinning. Under<112> tension, the atomic step nucleation on the surface of the ultra-thin nanobridges and then migrate along the surface. The nanobriges break by layer-by-layer peeling. Body-centered-tetragonal (BCT) lattice was observed during in-situ tension of gold nano-junction in a transmission electron microscope, which is well explained by the proposed deformation mechanism. In contrast to the well-known Bain model, the phase transformation can be realized by a progressively slipping process with a vector of1/12<112>. The lattice constant a can be accurately predicated from a hard-sphere model and c is about5%larger than that in MD simulations using a more realistic interatomic potential.SnO2, TiO2, CuO, SnO2/TiO2and Sn@CNTs one dimensional nanostructures were synthesized and their properties and behaviors under multi-field loading were studied by in situ TEM methods.Rutile SnO2/TiO2core-shell NWs have been successfully prepared via a two-step method based on thermal evaporation and atomic layer deposition. Structural characterizations reveal that rutile TiO2shells epitaxially grow on core SnO2NWs at low temperature (250℃). Non-conformal coating was observed for SnO2cores with rectangular shape. The TiO2growth rate depends on the surface orientations, which may be attributed to the different adsorption enthalpies associated with orientations. The octagonal shape of this heterostructure was explained by a proposed model based on the growth kinetics of ALE. Interestingly, conformal coating was found on an octagonal SnO2NWs with{100} and{110} surfaces. This model system demonstrates that the final morphology is determined by a combination of both kinetic and thermodynamic factors.Electrical failure study on semiconductor oxide nanowires (NWs) were performed in situ inside a transmission electron microscope (TEM). A high driven current leads to sudden fracture of the SnO2NW and creates ultra-sharp and high-aspect ratio tips at the broken ends, which provides a simple and reliable way for in-situ nano-probe fabrication. As a comparison, the TiO2NW fails due to Joule-heating-induced melting and retracts back into a nano sphere. The distinct behaviors root in the different bonding nature. Room temperature (RT) coalescence of double-walled carbon nanotubes has been observed for the first time. A combined pre-treatment of localized electron irradiation, Joule heating and electromigration leads to formation of large vacancy clusters, which can survive for tens of seconds during surface reconstruction. The dangling bonds of the edge atoms are highly reactive and thus promote the coalescence even at RT. The Sn@CNTs core-shell nanostructures were synthesized by CVD. Utilizing the this nanostructure, we realized the Sn metal transport along carbon nanotube by in situ TEM. Thermomigration introduce by electrical current was attributed to be the main reason.