Structural instability of a single crystal Si nanowire at room temperature under focused electron beam irradiation was investigated by our developed in-situ transmission electron microscopy observation technique. It was observed that a series of intriguing changes such as preferential amorphization at the surface of Si nanowire, local bulging in the radial direction and formation of a novel three layers-packaged coaxial structure of Si nanowire with the increasing of electron doses during the irradiation. The possible mechanism for such phenomena was proposed and further discussed by completely new concepts of nanocurvature effect and energetic beam-induced athermal activation effect, while the current knock-on mechanism and electron beam heating effect seemed inadequate to explain these processes
