錯位雙層石墨烯與單層石墨烯/過渡金屬硫族化物中電子-聲子交互作用之研究

A Study of Electron-Phonon Interactions in Misoriented Bilayer Graphene and Graphene/ Transition metal dichalcogenides Heterostructures

許慧姿(Hui-Tzu Hsu)

指導教授 ： 陳正中

國立清華大學/理學院/物理學系/碩士(2016年)

摘要

此論文的目的是透過量測單層石墨烯、錯位雙層石墨烯、單層石墨烯/二硫化鉬、單層石墨烯/二硒化鎢在不同費米能級時的拉曼光譜，觀察各樣品中電子-聲子交互作用的情形。
本文選擇以化學氣相沉積法成長大面積的石墨烯、二硫化鉬與二硒化鎢薄膜，再經過轉移製程，得到錯位雙層石墨烯與堆疊異質材料結構：單層石墨烯/二硫化鉬、單層石墨烯/二硒化鎢，並將薄膜製作成方便電性測量的四點量測元件，另外再塗佈上離子液體當作閘極，透過外加閘極電壓的方式來調控石墨烯的費米能級。
我們使用632.8奈米的氦-氖雷射，在室溫環境下量測各樣品在不同費米能級時的拉曼光譜，我們將以單層石墨烯的結果為標準，看其他樣品是否會與單層石墨烯有不同的趨勢。石墨烯的兩個主要拉曼特徵峰為G 峰與2D 峰，我們發現錯位雙層石墨烯的 I(2D)/I(G)強度比值隨著摻雜濃度的變化趨勢，與單層石墨烯的趨勢差異甚大，而單層石墨烯/二硫化鉬卻與單層石墨烯的趨勢相似，因此可以由I(2D)/I(G)對摻雜濃度的關係來判斷石墨烯的厚度是否為單層。
電子與聲子之間耦合力的大小會影響G 峰的偏移量，我們發現錯位雙層石墨烯的G 峰位置變化趨勢與單層石墨烯的趨勢相似，而在單層石墨烯/二硫化鉬以及單層石墨烯/二硒化鎢異質結構中G 峰位置變化趨勢都比單層石墨烯的趨勢要大，表示電子與G 峰聲子間的耦合力有增強的現象。

關鍵字

石墨烯 ； 過渡金屬硫族化物 ； 電子聲子交互作用

並列摘要

We investigate the Fermi-level (EF) dependence of electron-phonon coupling (EPC) in stacked graphene and graphene/transition metal dichalcogenides (TMD) heterostructures. The samples include single layer graphene (SLG), misoriented bilayer graphene (BLG), single layer graphene/molybdenum disulfide (SLG/MoS2), and single layer graphene/tungsten diselenide (SLG/WSe2). All materials were prepared by chemical vapor deposition and graphene transformation. We employ an ion-gel gate on top on graphene as a gate-electrode to tune EF. To reveal EPC, we use Raman spectroscopy to study the 2D or G peak shifts of graphene as a function of EF. The Raman spectra are measured at room temperature, with the 633-nm line of a He-Ne laser as exciting radiation. EPC can be characterized by the changes of G peak position with EF.
We find the changes of G-peak position in BLG are similar to the case in SLG, suggesting the weak induced EPC between two stacked graphene. Intriguingly, the G- peak position changes dramatically in SLG/MoS2 and SLG/WSe2. In contrast, the characteristic Raman peaks of MoS2 and WSe2 exhibit weak EF dependence. Data analysis suggests that the EPC strength is enhanced in SLG/MoS2 and SLG/WSe2 samples, and is increased with the increase of the carrier density. The increase of the EPC may be related to possible charge transfer in between the stacked layers. Our results provide useful information for the mechanisms of EPC for TMD heterostructures, and have strong implications in the device applications.

並列關鍵字

Graphene ； Transition metal dichalcogenides ； Electron-Phonon Interactions

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