Schematic diagram of the CVD setup.
(Color online) Structural images and EDS spectra of the SiOx nanowires after a reaction at 950 °C for 60 mins: (a) SEM image; (b) TEM image; (c) HRTEM image with SAED image in the inset; (d) EDS spectra.
SEM image of the SiOx nanowires grown at 950 °C for different durations: (a) In 20 mins the Ni thin film cracked, most melted with the substrate Si atoms, and began to agglomerate to form Ni-Si eutectic liquid droplets on the Si substrate. The arrows indicate the Ni-Si droplets with a brighter image. (b) In 25 mins the site density and size of the eutectic liquid droplets increased as a result of increasing duration for reactions. (c) In 30 mins nano Ostwald ripening of the catalyst droplets induced the coalescence of the droplets where some droplets leaded to nucleation or precipitation of SiOx nanowire and some adjacent catalyst droplets with nanowires coalesced to larger ones to induce thicker nanowires. (d) In 40 mins the adjacent catalyst droplets with nanowires continued to coalesce to larger ones to induce thicker nanowires; (e) In 50 mins SiOx nanowires in different diameters began to grow for different sizes of catalyst droplets. (f) In 60 mins with the above process continued, final long SiOx nanowires with their stepwide increased diameters grew in a tangled pattern.
(Color online) SEM images with a titled side view (left panel) and corresponding schematic diagrams (right panel) to illustrate in details how the SiOx nanowires with their stepwide increased diameters formed: (a) SiOx nanowires began to precipitate and nucleate underneath eutectic liquid droplets where the diameters of the wires were predominated by the eutectic liquid droplets; (b) nucleated SiOx nanowires grew where the nanocurved substrate may provided major source of Si atoms for the growth; (c) Along with the SiOx nanowires growth, some adjacent eutectic liquid droplets tended to aggregate or coalesce due to the high surface tension as induced by their nanocrvature; (d) Such an aggregation further leaded to growth of a thicker nanowire; (e) long SiOx nanowires with their stepwide increased diameters finally formed.
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