奈米碳尖錐上自組碳化鉻晶粒之成長與研究

Abstract

本研究利用偏壓輔助微波電漿化學氣相沈積(Bias assisted microwave plasma enhanced chemical vapor deposition)成長自組裝碳化鉻晶粒於奈米碳尖錐(CNTCrC)。 實驗結果發現一種由奈米碳化鉻晶粒自組裝於奈米碳尖錐的新材料。此一材料(CNTCrC)在掃瞄式電子顯微鏡(Scanning electron microscopy, SEM)下，不論在分佈及大小上均擁有極佳之均勻性。CNTCrC平均的直徑約為40至80奈米，隨添加之偏壓而改變，長度約為0.7微米。在穿透式電子顯微鏡(Transmission electron microscopy, TEM)下發現,碳化鉻晶粒僅存在於奈米碳尖錐的頂端，並且不同於奈米碳管，奈米碳尖錐被證實為為實心構造。在TEM繞射圖(Diffraction pattern)及低略角X光繞射(Grazing incident x-ray diffraction)中可證明碳化鉻具有結晶的構造，且經由計算可得到此碳化鉻成分為Cr3C2。 實驗中亦利用數個參數的變化去瞭解CNTCrC的成長。結果發現CNTCrC的成長是類似於奈米碳管的Vapor-liquid-solid機制，同時伴隨Vapor-solid機制，特別之處在於必須有足夠的負偏壓才能使CNTCrC成長。 在場發射的性質量測上，F-N曲線可證明CNTCrC具有場發射的性質，並且具有1.4V/um的起始電場。長時間的量測中，CNTCrC也具有良好之場發射穩定性。

In this study, hydrogen and methane gas mixture is introduced to grow self-embedded nanocrystalline chromium carbide on well-aligned carbon nanotips ( which is abbreviated as CNTCrC ) in bias assisted microwave plasma chemical vapor deposition ( BAMPCVD ). As a result, a new material with spherical chromium carbide on the top of carbon nanotips is demonstrated. Scanning electron microscopy (SEM) images show great uniformity on size and distribution. The CNTCrC grow up to approximately 0.7um in length and about 40 to 80nm in diameter by tuning the applied biases. Transmission electron microscopy (TEM) analysis shows that chromium carbide all exists on top of carbon nanotips. Unlike the hollow structure of carbon nanotubes, high resolution TEM images show the solid body of carbon nanotips. The TEM images and diffraction pattern show crystalline structure of the chromium carbide. We use grazing incident x-ray diffraction to investigate the chemical compound, which is attributed to be Cr3C2. Various parameters are introduced to understand the growth mechanism of CNTCrC. It indicated that the growth of CNTCrC is analogous to that of carbon nanotubes while sufficient negative bias is essential. The field emission measurement shows good I-V properties which turn on at 1.4 V/um and Fowler-Nordheim plot proves it to be field emission behavior. The field emission measurement shows good stability with applied field of 5 V/um for 10000 seconds with a current density of 200 uA/cm2.