分析石墨烯之電子場發射特性及其應用於掃描穿隧式電子顯微鏡

石墨烯是由單層碳原子所組成之二維平面結構，具有高深寬比、優秀的電子傳輸性，以及良好的機械性能；這些條件均顯示其極有潛力成為一場發射電子源。因此，若要深入探討其物理特性並加以應用，分析石墨烯邊緣之電子場發射特性為極其重要之關鍵。本研究探討石墨烯之製程以及邊緣之電子場發射特性。首先將高定向熱解石墨利用高溫熱焠火的方式冷卻於碳酸氫銨水溶液中，使其被剝離成為石墨烯；再使懸浮狀態之石墨烯固定於鎢針尖端，而成為石墨烯懸空探針。此時，即可利用場發射電子顯微鏡之設備，進行石墨烯邊緣之電子場發射實驗，並分析其特性。根據電子場發射實驗證實，石墨烯必須先經由高電場使其被啟動，再利用電壓升降數次之循環，以達到場發射電流穩定之程序；過程中起始電壓值隨著循環次數的增加而下降。當場發射電流達到穩定狀態時，起始電場值為3 V/μm，而電流穩定範圍為5.96 μA穩定性為4.6％。此外，我們由場發射電子顯微鏡獲得單層和三層石墨烯邊緣之原子解析圖像，證明石墨烯邊緣僅有少數優選原子會進行電子場發射；基於此特性，本研究成功地將單層石墨烯懸空探針應用於掃描穿隧式電子顯微鏡中，並與傳統掃描穿隧式電子顯微鏡之探針做比較。

關鍵字

電子場發射；石墨烯；掃描穿隧式電子顯微鏡

並列摘要

Graphene is a two dimension sheet of carbon crystal, it has shown excellent electrical conductivity and good mechanical properties, which reveal its potential to use for field emission electron source. We report the fabrication and field emission properties of graphene edges from a stable suspension graphene cantilever which prepared by rapid quenching of highly oriented pyrolytic graphite (HOPG) in an aqueous solution of NH4HCO3. Field emission properties were investigated using graphene assembled on a tungsten tip for instrumentation as field emission microscopy (FEM). Our field emission results show that stable field emission currents from graphene edges can be obtained after activated by using high electric field and careful conditioning process within several continuous testing cycles. During conditioning process, the turn on voltage settled. The characteristics of field emission from graphene edges show its turn on electric field of 3 V/μm at current of 5.96 μA with stability of 4.6％. Furthermore, we also obtained the resolved FEM patterns from single-layer and 3-layer graphene edges. There’s only optimal limited atoms will emits electrons from a graphene edge. Due to these property, we used our prototype free-standing single-layer graphene probe to applied in scanning tunneling microscopy(STM). Comparing with classic STM tip, the graphene probe have fairly good resolution in nano-meter scale.

並列關鍵字

Field emission ； Graphene ； Scanning tunneling microscopy

參考文獻

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分析石墨烯之電子場發射特性及其應用於掃描穿隧式電子顯微鏡

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