Silicon-Catalyzed Growth of Amorphous SiO_x Nanowires by Laser Vaporization of Si and Si/SiO₂

Abstract

Products from the laser vaporization of targets of four typesSi, (1:1) Si/SiO 2 , (1:9) Si/SiO 2 , and SiO 2 without the addition of any metal catalysts in the presence of high-pressure (0.9 MPa) Ar gas were characterized by transmission electron microscopy (TEM), high-resolution TEM, energy-filtered TEM, transmission electron diffractometry, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and powder X-ray diffractometry. Amorphous SiO x (0.8 ≤ x ≤ 2.0) nanowires (NWs) (10−40 nm in diameter and up to 1 μm long), having crystalline Si nanoparticles (NPs) covered with thin amorphous SiO x layers at the NW tips, were observed for the products from the Si and Si/SiO 2 composite targets, while only amorphous SiO x NPs were produced from the SiO 2 target. The O content relative to that of the Si in SiO x NWs was also increased with increasing the content of SiO 2 in the targets. We propose a novel mechanism for the growth of amorphous SiO x NWs, in which nuclei of the NWs are formed on the Si-rich molten SiO x NPs due to precipitation of SiO x via its supersaturation. Si acts as both a catalyst to precipitate SiO x and a source material of the NWs. A successive supply of Si, SiO, O, and others to the molten NPs, their diffusion and precipitation, and the oxidation of the precipitated NWs result in the further growth of the NWs.

Formation of Germanium-Carbon Core-Shell Nanowires by Laser Vaporization in High-Pressure Ar Gas without the Addition of Other Metal Catalysts

“…The larger diameter values of the NWs were plotted for the NWs grown at higher Ar pressures corresponding to the observation in the SEM and TEM images ( Figure 6). A strong correlations between the NP and NW diameters were evident, similar to the ones in our previous study of SiO x NW growth using Si and Si/SiO 2 targets [13]. formed by arc discharge [15].…”

“…targets was carried out in the presence of Ar gas as reported in previous studies [11] [12] [13]. Ge powder (Aldrich, 99.99% purity and 0.5 -147 μm grain size) was mixed with graphite powder (Toyo Tanso, 99.9% purity and ~4 μm grain size).…”

“…We have succeeded in forming some one-dimensional nanostructures, such as carbon nanotubes (CNTs) filled with Cu [11] or SiC [12] and amorphous silicon oxide (SiO x ) NWs [13] using continuous wave (CW) laser vaporization in high-pressure (0.1 -0.9 MPa) Ar gas without the addition of other metal catalysts. Our laser vaporization is a simple method, and it can grow composite one-dimensional nanostructures through a strong interaction of vaporized species with low expansion velocities (10 2 -10 3 cm/s) [14] in a confined space by high-pressure Ar gas.…”

Tailoring the shape of amorphous nanomaterials: recent developments and applications

“…The long-range disorder of amorphous materials generally makes them unable to form 1D nanostructures, which have obvious anisotropy, without any attached host [62] or particular guiding technique [63][64][65][66][67]. Nanotubes, NWs, and nanofibers are three typical types of 1D nanomaterials.…”

“…This process is similar to the laser vaporization-assisted approach used to grow amorphous SiO x NWs [65]. Amorphous NWs can also be prepared by the ways of CVD and plasma techniques [64,66,67].…”