金與鉀金屬輔助催化乙炔熱裂解製備碳奈米螺旋線及場發射研究

Abstract

我們證實以化學氣相沉積法的方式，並使用金與鉀金屬作為觸媒輔助乙炔熱裂解成長碳奈米螺旋線。在適當的反應參數下，能生長出均一形狀的碳奈米螺旋線，並經掃描式電子顯微鏡與穿透式電子顯微鏡鑑定為無晶相的螺旋碳纖維線。在每一根碳奈米螺旋線頂部存在一金屬顆粒，經能量散射圖譜與電子繞射圖形得知為金奈米顆粒，意味著此成長機制是以金為成核點的頂部成長機制。鉀的參與使反應溫度下降進而輔助乙炔的降解。我們認為在此反應中，acetylide與hydride中間產物形成，進一步地降解acetylide中間物造成固態碳沉積而使碳奈米螺旋線生長。改變反應條件對碳奈米螺旋線成長的影響亦被討論。我們提出金與鉀觸媒增強型頂部成長機制來解釋碳奈米螺旋線的生成。碳奈米螺旋線的電子場發射特性亦被研究。最好的電子場發射結果顯示起始電場為3.78 V m-1與場效增強因子為1852。此外，在電場為6.87 V m-1時，電流密度高達43 mA cm-2。此結果顯示碳奈米螺旋線在場發射裝置的應用上可望成為具有潛力性的材料。

We demonstrated that the growths of carbon nanocoils (CNCs) via chemical vapor deposition (CVD) using Au and K metals as the catalysts to assist the thermal decomposition of acetylene. Uniformly shaped CNCs, identified as amorphous coiled carbon fibers by scanning electron microscope (SEM) and transmission electron microscopy (TEM), were grown at proper combination of reactant parameters. A metallic Au nanoparticles (NPs), was determined by energy dispersion X-ray spectroscopy (EDX) and electron diffraction (ED), located at the tip of each CNC, suggesting that a tip-growth mechanism involving Au as the nucleation site was in operation. The K assisted the decomposition of C2H2 by lowering the reaction temperature. We suggest that in the reaction, acetylide and hydride intermediates were formed. Further decomposition of the acetylide intermediate deposited carbon solid for the CNC growths. Effect of varying the reaction conditions on the CNC growths was discussed. An Au and K bicatalyst enhanced tip-growth vapor-liquid-solid (VLS) mechanism was proposed to rationalize the CNC formation process. Electron field emission (EFE) characteristics of the CNCs were studied. The best EFE result showed a turn-on field (Eto) of 3.78 V m-1 and a field enhancement factor of 1852. In addition, the current density (J) was as high as 43 mA cm-2 at 6.87 V m-1. The results suggest that the CNCs could be promising candidates for field emission device applications.