氮化硼之鍍覆對奈米碳管場發射特性的影響

The Effect on Field Emission Characteristic of Carbon Nanotubes Coated by Boron Nitride Film

陳怡伶

指導教授 ： 蔡春鴻

國立清華大學/原子科學院/工程與系統科學系/碩士(2006年)

摘要

奈米碳管特殊的準一維結構，提供了一種本質上就具有高深寬比(aspect ratio)，且在尖端具有奈米級尺度的材料，更由於碳管優異的場致發射特性，因此被視為在場發射元件的應用上，具有高度的潛力與發展性。然而在長時間的操作下，環境的真空度變差，便會因為離子轟擊(ion bombardment)效應使得奈米碳管的場發射電流產生衰退，穩定度下降，本論文中嘗試以鍍覆氮化硼作為碳管表面的保護層，藉以降低離子轟擊對碳管的損傷，提高場發射的穩定度。
在本論文中，我們先以電漿輔助化學氣相沉積系統(Plasma-
enhanced Chemical Vapor Deposition，PECVD)合成高準直性(
vertically-aligned)的點陣奈米碳管，藉以降低屏蔽效應(screen
-effect)的影響，再將奈米碳管鍍覆上氮化硼材料，比較鍍覆前後對奈米碳管場發射特性的影響。
氮化硼亦是具有場發射特性的材料之一，在表面具有負電子親和力(negative electron affinity) ，並且具有高度的化學穩定度，氧化溫度約為800℃；在本實驗中我們利用兩種不同的合成方式鍍覆氮化硼，一為磁控濺鍍系統(Magnetron Sputtering System)，另一為電漿輔助化學氣相沉積法(Plasma-assisted CVD，PACVD)，實驗結果觀察到不同的合成方式所鍍覆之氮化硼，對碳管場發射特性之改質程度亦有所差別。
鍍覆氮化硼之奈米碳管，其場發射電流明顯增高，且起始電壓亦有下降的情況，單次量測之電流穩定度亦有改善的現象，此外，氮化硼鍍覆之厚度有一最佳厚度，當鍍覆之厚度大於此最佳厚度，場發射特性又會開始有衰退的現象。

關鍵字

奈米碳管 ； 場發射 ； 氮化硼

並列摘要

This thesis investigates the field emission characteristic of periodic arrays of vertically aligned isolated carbon nanotubes (CNTs) coated by boron nitride (BN) using magnetron sputtering method and plasma-assisted chemical vapor deposition method. It has been reported that BN film could be one of the promising materials for field emitter because of its negative electron affinity (NEA) at the surface. In addition to its high aspect ratio, the field emission characteristics of CNTs have been widely studied due to its chemically and mechanically robust properties. The synergism of the combination of these two materials on the field emission mechanisms was investigated in this work. Vertically aligned CNTs were synthesized using catalytic chemical vapor deposition (CCVD) method to avoid screen effects due to high density of CNTs. After that, the periodic arrays of vertically aligned isolated CNTs coated with BN film were fabricated. The comparison between those with and without BN coating revealed a significant effect of the thickness and the NEA characteristics of BN coating on the field emission properties. The electron pathway and the field emission mechanisms of BN coated CNTs will be further discussed.

參考文獻

[11].成會明，奈米碳管Carbon naotube 初版,(2004)五南出版社:13

[13].成會明，奈米碳管Carbon naotube 初版,(2004)五南出版

Electronics, (2001), vol.45(6)：963-976

[5].N. Koshida et al., (1995), J. Jap. Appl. Phys., 34：L705

[8].Iijima S, Nature. (1991), 354: 56