利用鉀金屬輔助化學氣相沉積低溫裂解乙炔製備奈米碳纖維

Abstract

於本論文中，我們利用化學氣相沉積法在高濃度的氫氣環境下，伴隨 鉀金屬催化輔助乙炔在低溫裂解，成功製備出奈米碳纖維。並且在反應後， 能夠藉由去離子水沖洗，輕易地去除所使用的鉀金屬，得到無金屬殘留的 奈米碳纖維。經由穿透式電子顯微鏡之繞射，鑑定此方法合成之一維碳材 料為無晶相的奈米碳纖維。根據實驗所觀察之結果，我們提出鉀金屬催化 的氣液固相反應的成長機制。在反應過程中，液相的鉀金屬在高溫下輔助 乙炔裂解成非晶相的碳，然後在鉀金屬之間沉積，並持續的將部分的液態 鉀金屬往上拉升，形成一維的碳纖維。經由此方法所合成的奈米碳纖維， 在場發射的特性上，具備高穩定性、低起始電場(Eto : 2.63 V/μm)、高場發射電流密度( Jmax : 12.5 mA/cm^2 於 5.50 V/μm 電場下)及高場增強因子(β: 1650)。並且經由電化學方法量測，顯示此奈米碳纖維電極，具備高表面積的優勢。此特性使得奈米碳纖維，在場發射裝置及電極的應用上，可望成為具有潛力的材料。

Amorphous carbon nanofibers (a-CNFs) were grown on Ti foils using K as the catalyst to assist the thermal decomposition of C2H2 in a H2-rich environment at 723 K. After K was removed with water, a-CNFs with lengths up to tens of um and diameters 30 - 80 nm were observed. The growth of a-CNFs depended on the reaction conditions highly. A vapor-liquid-solid (VLS) growth mechanism is proposed to rationalize the growth process. The electrochemical surface area (ESA) of an a-CNFs on Ti sample (geometrical surface area 0.194 cm^2 ) was determined to be 0.386 cm^2. The field emission properties, turn-on field Eto and field enhancement factor b, of an a-CNFs on Ti were determined to be 2.63 V/um and 1650, respectively, while Jmax reached 12.5 mA/cm^2 at 5.50 V/um. The field emission current sustained up to 15 h at the applied voltage.