| With the background of nanoscience and nanotechnology,materials research is moving toward revealing structure and property of materials not only at nanometer scale(or under extremely small space limitation)but also at nano-,pisco-,or femto-second scale(or under extremely short time limitation).In recent years,energetic electron beam-induced the structural nanoinstability of low dimensional nanostructures(LDNs)has been reported.However,people have to resort to the existing concepts,such as the classical knock-on mechanism and its related molecular dynamics simulations to explain the structural instabilities of LDNs.In these reports,the nanocurvature effect of LDNs and the athermal activation effect of energetic electron beam have been neglected,which have been predicted to be the key factors to affect the structural instability of LDNs.Hence,a systematic investigation into the nanocurvature effect of LDNs and the athermal activation effect during the energetic electron beam induced structural transformation of LDNs is imperative.In order to investigate further the nanocurvature effect of LDNs and the beam athermal activation effect,in this thesis,in transmission electron microscopy,we in-situ investigated the electron beam-induced structural instability of amorphous SiO_x nanowire(NW)specifically of four different configurations at room temperature.These configurations include:i)straight NW fixed at two ends;ii)straight NW fixed at only one end fixed;iii)axially curved NW fixed at two ends;iv)straight NW not fixed at two ends.It was revealed that i)the straight NW fixed at both ends shrank in its diameter uniformly;ii)the DWCNT fixed at only one end intriguingly shrank preferentially from its free cap end along its axial direction whereas its diameter shrinkage was offset;iii)the axially curved NW fixed at two ends turned straight quickly accompanied with a uniform axial shrinkage and a uniform radial expansion intriguingly;iv)the straight NW not fixed at two ends demonstrated a tensile pulling-free uniform plastic elongation and an accelerated uniform radial shrinkage at the nanoscale intriguingly.A mechanism of "diffusion" along with "evaporation" at room temperature which is driven by the nanocurvature of the amorphous SiO_x NW and the athermal activation induced by the electron beam was proposed to elucidate the observed phenomena.It is expected that such an investigation has important implications for the processing or stability of future NW-based structures or devices.More importantly,it further demonstrates that the nanocurvature effect and the athermal activation effect of energetic electron beam,which have been normally neglected or inadequately taken into account in the current literature,are universal concepts and applicable to explain the energetic electron beam-induced LDNs nanoinstabilities. |
