Self-Templating Assisted Growth of Silicon Carbide Nanostructures

• Main Authors: Chia-Hsin Wang, 王嘉興
• Other Authors: Hsin-Tien Chiu
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/63879963519514745376

博士 === 國立交通大學 === 應用化學系所 === 95 === In this thesis, we employ phase segregation as the concept to develop diverse SiC nanostructures via vapor-liquid and vapor-solid reactions. Inorganic salts MClx (M=Na, Mg, Ca) act as templates generated in-situ to assist the morphology development. First, cubic shells and spherical nanoparticles of 3C-SiC were produced at 1273 K by processing the ceramic precursors formed from the reactions between vapor of organochlorosilanes, Me2SiCl2, MeSiCl3, MeSiHCl2, and PhSiCl3, and liquid Na at 523 – 723 K. From Me2SiCl2, a flexible linear polycarbosilane precursor was synthesized and covered the NaCl byproduct surface to from a cubic shape. Hollow cubic 3C-SiC shells were produced after the NaCl templates were removed. From MeSiCl3, a rigid cross-linked polycarbosilane was produced and phase segregated from the NaCl byproduct. The precursor was transformed into nanoparticles without special morphology. MeSiHCl2 produced a cross-linked polysilane precursor at low temperatures, which can be converted into a mixture of 3C-SiC and Si nanoparticles. At high temperatures, the polysilane converted to polycarbosilane and produced hollow cubic�n��-SiC shells. The carbon-rich PhSiCl3 generated cube-like particles as the final product, which contained 3C-SiC and carbon. In the second section, polycrystalline tubular SiC on Si was prepared by reacting MeSiHCl2 vapor and Ca thin film on Si at 773 - 923 K followed by heat-treatment at 1273 K. The products phase-segregated into a cable-like radial heterostructure composed of a core of CaCl2 and a shell of SiCxHy. After removal of the CaCl2 core, the layer of polycrystalline SiC tubes on Si emitted electrons at a low applied field of 2.5 V/ μm with a current of 10 μA/cm2. In the third section, we also used the phase segregation concept in the reaction of Me2SiCl2 and MeHSiCl2 between and magnesium metal at 823 - 923 K. The product was heat treated at 1273 K under vacuum. It showed pseudo thin plate SiC nanostructure, which was self-templated by MgCl2 generated in situ. In the fourth section, we extended the phase segregation idea to create porous SiC thin film on Si subtrate. Using Sn(SiMe3)4 as the precursor, amorphous SixC1-x thin films with Sn nanoparticles embedded were grown on Si substrates at 923 K by low pressure chemical vapor deposition. After treated under hydrogen plasma at 923 K, the Sn nanoparticles in the films were removed by an HF solution and by evaporation at 1423 K. Following the removal of Sn, high temperature treatments at 1273 - 1423 K converted the amorphous thin films into mesoporous semiconducting 3C-SiC thin films with pore sizes 10 - 100 nm. Finally, one dimensional high aspect ratio Au nanowires were fabricated via galvanic reduction of HAuCl4 solution in the presence of cetyltrimethylammonium chloride (CTAC) by the Sn nanoparticles embedded in amorphous the SixC1-x thin film product.