Fabrication, Decoration, And Processing Of SiO_x Amorphous Nanowire

SiO_x nanowire with its unique properties holds a lot of prospective applications in fields such as optical communication, optical sensing, catalyzing, and environments sensing etc. Many methods were attempted for SiO_x nanowire fabrication and several corresponding growth mechanisms were proposed for elucidating, among which vapor-liquid-solid(VLS) mechanism is the most widely accepted. Nevertheless, even with the VLS mechanism, complicated chemical processes are normally involved and thus the overall growth is controlled by a variety of parameters such as temperature, pressure, and gas flow within the reactor chamber. Even geometry, shape, and setting arrangements of the reactor chamber and some uncertain factors have effect on the final products. Therefore, the growth process and relevant details for the VLS mechanism is not yet fully understood. However, a full understanding of the growth process and relevant details for the VLS mechanism is crucial to precisely controlled growth of SiO_x nanowire as well as the related applications.With the above considerations, in the present thesis, a laser-assisted chemical vapor deposition system was built, in which heating furnace and reactor chamber were designed as small as possible so that temperature, pressure, and gas flow within the chamber can be kept uniform and accurately controllable as much as possible. Via this system, a grey product which was powder-like to naked eyes was obtained by a simple method. The powder-like product was further characterized to be amorphous SiO_x nanowires via SEM, TEM, SAED and EDS. After that, with a precise control of temperature, gas flow, and pressure and with sequentially increasing durations for the different reactions, respectively, at 20min,25min,30min,40min,50min,60min, the detailed processes of catalyzing, nucleation, and growth of the SiO_x nanowires were successfully traced. Especially a stepwise non uniformity in diameter of nanowire during the growth was for the first time detected. With analysis of these detailed processes, a deeper understanding of the vapor-liquid-solid mechanism was achieved and a novel mechanism for formation of the stepwise non uniformity in diameter of nanowire was particularly proposed. All these will be the crucial basis for our further, accurately controlled growth of SiO_x nanowires and the relevant applications.On the other hand, the structure of the as-grown amorphous SiO_x nanowires is intrinsically thermodynamically instable due to its nanosize effect, especially its surface nano curvature effect. Taking advantages of this kind of structure instability, we further precisely decorated and processed the SiO_x nanowires so that they can well suit many potential applications in optoelectronic nanodevices. Herein, for the decoration, with a sputtered gold deposition on the as-grown SiO_x nanowires and a following-up annealing at high temperature, a novel nanocomposite of SiO_x nanowire decorated with gold nanoparticles on the wire surface was fabricated. At the same time, a highly localized, coreshell-like SiO_x nanowire was synthesized for the first time via mass transfer among different instable nanowires under irradiation with normal e-beam during in-situ transmission electron microscope observation. For the nano processing, a new treatment for the as-grown SiO_x nanowire by in-situ focused e-beam irradiation with different beam spot sizes and positions was performed in electron transmission microscopy. It was found that diameter shrinkage of the nanowire is a widespread phenomenon under focused e-beam irradiation. It was further observed that a tangential irradiation with a beam spot size smaller than the diameter of the wire caused an obvious cutting effect on the wire, whereas a central irradiation at wire axis position with a beam spot size larger than the diameter of the wire induced an intriguing S-type deformation of the wire within local, irradiated zone in addition to the diameter shrinkage of the wire. With a comprehensive analysis, it is revealed that the nanocurvature effect of the nanowire and the soft mode effect during beam ultrafast irradiation as we recently proposed are dominating driving forces to induce the nano decoration and the nano processing.