利用化學氣相沉積法在不同基板上成長石墨烯

Abstract

本論文主要是探討石墨烯直接成長在銅箔、藍寶石基板的形成機制上差異和背向閘極電晶體元件特性的比較。銅箔成長方面藉由改變甲烷氣體的分壓來控制成長單晶石墨烯的成長速度，我們可控制前置熱處理的時間提升銅箔的平整度，藉此降低表面石墨烯晶種的密度。將銅箔上的石墨烯轉印後搭配拉曼頻譜的量測來檢驗石墨烯的品質，在背向閘極電晶體特性上單晶區域較大的石墨薄膜載子遷移率有明顯上升。另外藍寶石基板成長方面，我們成功在藍寶石基板上成長石墨烯，並用AFM、SEM、TEM、XPS等量測來檢驗在藍寶石基板成長的石墨烯，藉由改變氫氣及成長時間來改善薄膜品質。這種石墨烯薄膜成長的優勢為可避面轉印時造成的汙染及破損，讓石墨烯可以非常平整，這結果可以讓現今的二維材料能夠有更多的發展性。

The main focus of this thesis is on the fabrications of graphene films on Cu foils and directly on sapphire substrates by using chemical vapor deposition (CVD). The formation mechanisms and the characteristics of the graphene films are investigated. The device performances of the back-gated graphene transistors are also investigated in this thesis. For the graphene films grown on Cu foil, by changing the methane gas partial pressure, the graphene growth rate can be controlled. By increase the pre-growth annealing time, the graphene flake density is rapidly reduced. By transferring the films to SiO2/Si substrates, micro Raman measurements are performed on the graphene films to verify their crystalline qualities. It is observed that the graphene transistor performances are highly dependent on the sizes of the graphene flakes. For the graphene films grown on sapphire substrates, high-quality and large-area films are obtained on sapphire substrates without the assistance of metal catalyst. The graphene film characteristics are investigated by AFM, SEM, TEM, XPS etc. By changing the hydrogen gas flow rate and growth time, the graphene film quality can be greatly improved. The metal catalyst-free growth of graphene film on sapphire substrates has the advantage of application without the necessity of using a metal substrate as a catalyst and the following metal removal process. Because the graphene films prepared by using this method are very smooth on the surface, the development of this growth approach can be very advantageous for the practical applications of the 2-D materials.