身為第一個成功被發現的二維材料，石墨烯的各項獨特性質都吸引了各領域研究者的目光，如其極高的透光度和超快的電子遷移率等。然而，因為缺乏製作穩定的大面積高品質石墨烯薄膜方法，石墨烯的應用受到了侷限。在過去將近十年的時間裡，各式各樣的石墨烯製作方法如雨後春筍般地被開發了出來。其中，化學氣相沉積法(CVD)被視為最具有研究價值的方法之一。與其他方法製作的石墨烯相比，藉由CVD所產出的石墨烯薄膜不僅連續，且可以大面積的製造，這使得CVD石墨烯的前景受到了大幅度的關注。儘管如此，CVD石墨烯仍有晶粒邊界的缺陷需要被克服。晶粒邊界不只削弱了石墨烯薄膜的強度，同時還減低了電子遷移率。因此，如何減少這些晶粒邊界、製作出大面積的單晶石墨烯已被視為提高CVD石墨烯品質的關鍵之一。 在這篇論文研究中，我們展示了利用一個爐管系統來製造公釐(mm)尺寸的石墨烯單晶成長方法。藉由探討對甲烷和氫氣的比例以及生長溫度的效應，我們找到了一個適合大面積石墨烯單晶的成長條件。此外，在這些大面積石墨烯單晶之下，我們還發現了一些低層數的小石墨烯單晶。因此，我們重新再探討了一次生長溫度的效應，發現銅的昇華對我們的系統有不容忽視的影響。這些小單晶之所以只能出現在這些大單晶底下可以被歸因於銅昇華的效應。銅的昇華會移除掉尺寸比較小的石墨烯，只有藉由大尺寸石墨烯的覆蓋，這些小石墨烯才有機會在銅昇華影響比較小的情形下獲得成長。我們希望這篇研究可以對於大尺寸的石墨烯單晶以及多層石墨烯的成長機制有所幫助。 ;As the first identified 2-dimentional material, the unique properties of graphene, such as the ultrahigh electron mobility, had attracted lots of researchers in the related fields. However, the lack of large area and high quality graphene limited the application of graphene-based devices. In the past 10 years, a lot of graphene fabrication methods had been developed. Among these methods, CVD was seen as one of the most promising ways for graphene fabrication. CVD graphene is based on the need of large area continuous graphene films. However, the quality of CVD graphene films would be limited by the grain boundaries. The grain boundaries would reduce not only the stiffness of graphene films but also the electron mobility. Hence, how to reduce the effect of grain boundaries in CVD graphene became an important issue in related applications. The growth of graphene single crystals had been considered as a key to improve the quality of CVD graphene. In this study, we would demonstrate the growth of millimeter sized single crystalline graphene by a furnace CVD system. By visiting the effect of hydrogen to methane ratio and the effect of growth temperature, we found a suitable growth condition for large graphene single crystals. Besides, under the mm-sized graphene single crystals, we also found the growth of smaller few-layered graphene. Hence, we revisited the effect of growth temperature and found the sublimation of copper played an important role in the system. The reason the smaller grains could only appeared under large grains could be attributed to the copper sublimation would remove the smaller grains. The coverage of the large grains could limit the copper sublimation and created an environment for the smaller grains. We hoped this study could provide some idea about the growth mechanism of large area single crystals and multilayered graphene.
