Preparation Of Silicon Nanowires And Nanotubes By Hydrothermal Method And Research On Their Growth Mechanism

Quasi one-dimension silicon nanomateials such as silicon nanowires (SiNWs) and silicon nanotubes (SiNTs) with quantum confinement effects and small size effects are new kinds of optoelectronic materials. Since silicon nanomaterials are compatible with modern silicon technology, they are promising in nanodevices and will dominate in semiconductor industry. Although the valence electrons of silicon atoms are apt to sp3 hybridization which promote the formation of SiNWs rather than the tubular one, theoretical calculation suggests that silicon atoms may be sp2 hybridization under appropriate conditions and accumulate as graphite-like sheets. Once the silicon sheet is formed, it is easier to bend as tubular structure than carbon. Though self-assembled SiNT was still challenging, under appropriate conditions it can also exist. In this paper we will discuss the preparation of SiNTs and SiNWs by hydrothermal method. In our experiment SiNWs were prepared using SiO as the start material and de-ionized water as reaction medium under 470℃ with the pressure near 11.9 MPa in a sealed reaction kettle. Using the same start silicon source, SiNTs were also prepared with the pressure cortrolled from 6.8 MPa to 8.0 MPa. The diameter of SiNTs and its hollow structure were decrease with the increase of pressure in the reaction kettle. Using SiC and SiO2 powder as the start material and de-ionized water as reaction medium, with the similar growth condition of SiNTs, we succeeded in preparing SiC nanotubes (SiCNTs). Silicon nanochains were found in the production with Si powders as start materials and de-ionized as reaction mediums under 470℃ with the pressure near 9.7 MPa in reaction kettle, the crystal structure of silicon nanochains was orderliness. None of SiNWs, SiNTs or SiCNTs was prepared only using SiO2 or SiC powder as start material under the similar condition of SiNTs and SiNWs growth. The structure and composition of the production were characterized by transmission electro microscopy (TEM), high-resolution transmission electro microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive X-ray spectrum (EDS). No metallic catalysts were added, so the obtained SiNTs, SiNWs, SiCNTs had no metal contaminations. The growth process of silicon nanomaterials is the atomic self-assemble course and the productions have good crystal structure. The growth mechanism of SiNWs and SiNTs by this method is not like the traditional VLS mode. In the last part of the paper we will discuss the self-assemble growth mechanism of silicon nanomaterials by hydrothermal method.