- 學位論文
以熱裂解氣相沉積法裂解甲烷成長奈米碳管
Carbon nanotubes synthesized by chemical vapor deposition of pyrolytic methane
摘要
本文主要探討，以熱裂解法裂解甲烷在摻催化劑的矽基板上成長奈米碳管。我們以將以兩種熱裂解甲烷成長奈米碳管的方法來作比較，討論兩者所成長的奈米碳管的差別：我們以表面型態、結構以及場發射特性作為探討的依據。 首先，以微波輔助加熱裂解甲烷來成長奈米碳管。此方式的優點在於操作時間很短，且奈米碳管的產量很大，純度也很高；缺點是，無法定義出成長奈米碳管的溫度，且受制於微波功率的不穩定，產生不穩定的成長環境，因而造成實驗參數的不確定性。此種加熱法所成長出的碳管，由掃描式電子顯微鏡(SEM)的觀察得知，直徑大約是100 nm左右；由穿隧式電子顯微鏡(TEM)的觀察可以了解，在不穩定的成長環境下，管壁的結構並沒有很完整；也由於管壁的缺陷多，導致場發射的特性不佳，其電流密度約為0.12 mA/cm2，而起始電場約為1.2 V/μm。 其次，用高溫爐加熱裂解甲烷進行氣相沉積來成長奈米碳管。由於高溫爐有極佳的溫度控制，可以精確地定義出奈米碳管的成長溫度；此外，由於成長環境變化小，可以對各種參數的變化有著更精確的掌控。以這種加熱法所成長出來的碳管，由SEM的觀察可知其直徑大約是50〜100 nm；由TEM的觀測看出，管壁的結構明顯地比前一種的結果要來得好。在場發射量測方面，電流密度最高可達7 mA/cm2，起始電場為1.35 V/μm，可見，不易毀壞的發射源改善了場發射的特性。
並列摘要
This thesis mainly expounds the growth of carbon nanotubes (CNTs) by thermal chemical vapor deposition (CVD) on p-type Si wafer coated with transition metal as catalyst. The catalysts used are and FeCo thin film. CNTs synthesized by two kinds of heating methods were compared in regard to their morphologies、structures and characteristics of field emission. In the first method，for the pyrolysis of methane microwave-heating thermal CVD (MHT CVD) were used to grow CNTs. The advantages of this method are the shortening of processing time and the output of rich、pure CNTs. The shortages of this method are the difficulty of defining growth temperature and the lack of stability of microwave power. From the images of scanning electron microscope (SEM)，the diameter of CNTs synthesized by this method is about 100 nm；The instability of the microwave power causes the defect-specked walls of CNTs as observed from the tunneling electron microscope (TEM) images；besides，due to the defects along the walls，the characteristics of field emission of these CNTs are not so good，with current density of 0.12 mA/cm2，and turn-on field of 1.2 V/μm. In the second method，CNTs were synthesized by thermal CVD in a furnace. Growth temperature could be defined ，and other growth parameters were under control due to the stability of the growth environment In this case. From the SEM images，the diameter of these CNTs ranges between 50 to 100 nm；the structure and the field emission characteristics of these tubes are better than former ones，current density of 7 mA/cm2，and turn-on field of 1.35 V/μm，are obtained. Defects in the tubes seem to play a role improving the field emission property of the CNTs.