化學氣相沉積之鉀與銀金屬共同輔助乙炔分解製備碳奈米螺旋線

Abstract

於本論文中，我們利用化學氣相沉積方法於鉀與銀金屬之共同輔助乙炔分解製備碳奈米螺旋線。利用氫化鉀於623 K 裂解產生之鉀金屬具有易丟電子之特性，對帶有偏酸性氫原子之乙炔進行催化反應，同時利用銀奈米顆粒於矽基材表面所形成的活性成長位置，於723 K 以及以氫氣作為載流氣體成長碳奈米螺旋線。論文中控制實驗參數探討實驗之變化，根據實驗所觀察之結果提出一個可能的成長機制。 控制反應時間所得到不同長度以及經過熱處理之碳奈米螺旋線作場發射的性質量測，反應60分鐘經熱處理之碳奈米螺旋線具有良好的場發射性質：低電子場發射起始電場 (Eto: 2.51 V/μm)、高電子場發射電流密度 (Jmax: 17.71 mAcm-2 at 5.64 V/μm) 以及高場增強因子 (β: 2124)。利用電化學之方法，於幾何面積為0.078 cm2之碳奈米螺旋線電極具有相當大的電化學活性表面積為0.143 cm2。此特性使碳奈米螺旋線組成之電極具備更進一步於電化學上應用之潛力。

Growth of amorphous carbon nanocoil (CNC) from acetylene on Si substrates was achieved by using nano-sized Ag and K as the catalysts. The deposition of CNC was carried out inside a hot-wall reactor at 723 K using H2 as the carrier gas. Based on the observed results, we propose a cooperative bimetal catalysts enhanced vapor-liquid-solid (VLS) growth mechanism to rationalize the CNC growth. In the reaction, the liquid phase metallic K dehydrogenates acetylene into the solid-state carbon while the Ag nanoparticle assists 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 curls 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 μA/cm2) at a turn-on field Eto of 2.51 V/μm while Jmax reached 17.71 mA/cm2 at 5.64 V/μm. The field enhancement factor β 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 K3[Fe(CN)6] via cyclic voltammetry (CV). The electrochemical surface area of a CNC electrode (geometric surface area 0.078 cm2) was calculated to be 0.143 cm2. These properties suggest that the CNC electrodes may have potential applications in field emission and electrochemical devices.