微波電漿化學氣相沉積系統製作混合碳奈米纖維／碳化矽錐形奈米結構

Fabrication of Cone-Shaped CNF/SiC-Coated Si-Nanocone Structures by Microwave Plasma Chemical Vapour Deposition

本文介紹以微波電漿化學氣相沉積系統製備出一結合碳奈米纖維與碳化矽且具有優異場發射性質的新穎錐形複合結構。穿透式電子顯微鏡分析結果顯示，該新開發的錐形複合結構其頂端的碳奈米纖維乃鯡魚骨狀類型同時包含竹節狀結構，而底部的奈米錐為碳化矽層包覆單晶矽平頂結構。利用此碳奈米結構作為場發射元件時，其驅動電場強度可下降到0.32 V mm-1（於電流密度達10 mA cm-2），發射電流密度在電場強度1.05 V mm-1下可上升至668 mA cm-2，且具有極大的場效增強因子~48349。此外，在電場強度1 V mm-1條件下，電流密度仍可維持在200 mA cm-2超過260分鐘沒有明顯的衰退。該結構具有優異的場發射特性可歸因於具有竹節狀結構的鯡魚骨類型碳奈米纖維有著更多開放的石墨片層邊緣以及頂端具有尖角形貌，同時底部錐形的碳化矽/矽結構提高與基材間的附著力。此結果意味著該錐狀複合結構乃一極佳場發射材料。 Novel cone-shaped carbon nanofi ber(CNF) /silicon carbide(SiC) -coated Si-nanocone(Si-NC) composite structures with excellent field emission(FE) performance have been fabricated by microwave plasma chemical vapour deposition(MPCVD) . Transmission electron microscopy analyses reveal that the newly developed cone-shaped composite structures are composed of bamboolike herringbone CNFs grown vertically on the tips of conical SiC layers with a fl at-top Si cone embedded underneath. For this CNF/SiC-coated Si-NC composite array, a ultra-low threshold fi eld of 0.32 V mm-1(at 10 mA cm-2) , a large emission current density of 668 mA cm-2 at 1.05 V mm-1, and a field enhancement factor as high as ~48349 are obtained. In addition, the FE lifetime test performed at a large emission current density of 200 mA cm-2 under an applied field of 1 V mm-1 shows no discernible decay during a period of over 260 minutes. We deduce that this superior FE performance can be attributed to the specifi c bamboo-like herringbone CNFs with numerous open graphitic edges and a faceted top end, and the conical base SiC/Si structures with suffi cient adhesion to the substrate surface. Such a novel structure with promising emission characteristics makes it a potential material for electron fi eld emitters.