Study On SWCNT Structure Instability As Induced By In-situ Transmission Electron Microscope Electron Beam Irradiation

Under driving of nanotechnology, the frontier of materials fundamentals research are commencing to reveal structures and properties 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 this regard, a systematic investigation into nonequilibrium, highly localized, and ultrafast interaction of energetic beam with low dimensional nanostructures is especially meaningful: it not only can provide crucial guideline and reference for nanomaterials or nanodevice fabrication and processing but also can reveal the fundamental issues of nanoscience such as nanocurvature-related nanospace effect of low dimensional nanostructure and althermal activation-related nanotime effect of ultrafast energetic beam.In this thesis, on the basis of the previous research on the structural instability of nanocavities in silicon and germanium as induced by energetic beam irradiation, we further systematically studied the structural instabilities of single-walled carbon nanotubes (SWCNTs) of three typical settings under electron beam irradiation by our developed in-situ transmission electron microscopy observation technique. The three typical SWCNT settings included: 1) a straight SWCNT is fixed at only one end with the other end free standing; 2) a straight SWCNT is fixed at both ends; 3) a SWCNT is bent along axis direction,. The experiments showed that 1) the tube fixed only at one end preferentially shrunk in axis direction first, then shrunk and necked in diameter, and finally formed a carbon cage-like strand structure at the tube free end; 2) the tube fixed at both ends merely shrunk and necked in diameter with the similar formation of carbon cage-like strand structure; 3) the tube bent along axis direction shrunk in axis direction much faster than the straight tube. The experiments especially revealed that the necked carbon cage-like strand structure in the case 2) was able to re-fuse after breaking and thus demonstrated a strong wetting ability and an amazing athermal plastic flow on the surface of the SWCNT fixed at both ends under the electron beam irradiation at room temperature. The experiments demonstrated in general that 1) the more cureved SWCNT, the more instable; 2) electron beam can athemally activate the SWCNT structural instability.We fully discussed, modeled, and well explained the above nanocurvature effect of SWCNT structure and the athemal activation effect of electron beam irradiation on the SWCNT structural instability using the general concept of low dimensional nanostructure nanocurvature and the soft mode and that of the energetic beam–induced soft mode and lattice instability as we recently proposed. The above explanation broke through the limitation of the current classic knock-on mechanism explanation and the related molecular simulation for the interaction of electron beam with carbon nanotube and the induced structural changes. The thesis thus further justified, consummated and extended the concept of low dimensional nanostructure nanocurvature (nanospace) effect and that of energetic beam induced-soft mode and lattice instability (nanotime) effect and the nanoscience subject in general.