Browsing by Author "Liu, Wen-Chih"

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Growth of Carbon Nanocoils from K and Ag Cooperative Bicatalyst Assisted Thermal Decomposition of Acetylene
(2010-07-01)
Liu, Wen-Chih
;
Lin, Huang-Kai
;
Chen, Yu-Liang
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
Growth of amorphous carbon nanocoil (CNC) from acetylene on Si substrates was achieved by using nanosized Ag and K as the catalysts. The deposition of CNC was carried out inside a hot-wall reactor at 723 K using H(2) as the carrier gas. Based on the observed results, we propose a cooperative bimetal catalyst enhanced vapor-liquid-solid (VLS) growth mechanism to rationalize the CNC growth. In the reaction, the liquid phase metallic K dehydrogenated acetylene into the solid-state carbon, while the Ag nanoparticle assisted the extension of carbon one-dimensionally (1-D) via a tip-growth mechanism. Due to the adhesive force between the K liquid and the carbon, the 1-D solid curled along the C K interface into the nanocoil shape. Some CNC samples were further heat-treated at 1423 K and showed very good field emission properties. They emitted electrons (10 mu A/cm(2)) at a turn-on field E(10) of 2.51 V/mu m, while J(max) reached 17.71 mA/cm(2) at 5.64 V/mu m. The field enhancement factor beta was calculated to be 2124, comparable to other carbon nanotube (CNT) and CNC based emitters. The CNC was also characterized by using the electrochemical behavior of K(3)[Fe(CN)(6)] via cyclic voltammetry (CV). The electrochemical surface area of a CNC electrode (geometric surface area 0.078 cm(2)) was calculated to be 0.143 cm(2). These properties suggest that the CNC electrodes may have potential applications in field emission and electrochemical devices.
Silicon carbide nanostructures from reactions between vapors of organochlorosilanes and liquid of sodium-factors affecting morphology and composition
(2007-12-01)
Wang, Chia-Hsin
;
Liu, Wen-Chih
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
;
應用化學系
Cubic shells and spherical nanoparticles of beta-SiC were produced at 1273 K by processing the ceramic precursors formed from the reactions between vapors 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 form a cubic shape. Hollow cubic beta-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 beta-SiC and Si nanoparticles. At high temperatures, the polysilane converted to polycarbosilane and produced hollow cubic beta-SiC shells. The carbon-rich PhSiCl3 generated cube-like particles as the final product, which contained beta-SiC and carbon.