石墨烯的微波元件研究

Abstract

石墨烯是由單層碳原子所組成的六角晶格結構，有著高電子遷移率以及反常的量子霍爾效應等有趣以及優異的物理特性，因而被廣泛的研究，像是石墨烯的DC 傳輸量測以及拉曼、光致發射、和紅外光譜等實驗研究，但卻鮮少有石墨烯在量子霍爾領域的微波實驗，因此本論文的研究目標是希望藉寬頻微波量測觀察石墨烯在量子霍爾領域以及微波頻率下的動態反應，本論文會先研究石墨烯微波元件製程方法，由石墨烯的位置定位到共平面波導的設計以及製程，並確認了其微波元件能夠達到阻抗匹配。本論文有兩種石墨烯的微波元件，一種是石墨烯位於中心線與接地面之間，而另一種是位於中心線與中心線之間，而後者與前者的製程差異在於後者會加上由NiCr作成的電阻，其製程方式是藉由蝕刻液來調整NiCr的幾何形狀來達到阻抗匹配。 量測方面則是在低溫（1.5 K）高磁場下（8 T）分別使用AC及DC量測，本論文在DC的量測中觀察到了量子振盪（quantum oscillation），且觀測到AC量測的數據與DC量測的數據會有一樣的趨勢，最後本論文建立了一個分析模型嘗試將S-parameters據轉換成AC電導。

Graphene is a hexagonal lattice structure of a single-layer carbon atoms with a high electron mobility and other excellent physical properties, and the cleavage technique led directly to the first observation of the anomalous quantum Hall effect. Graphene has been widely investigated via various techniques such as DC transport measurements, Raman spectroscopies, photoemission, infrared spectrum, ...etc. However, there are very few experimental studies regarding microwave spectroscopy of graphene, especially in the quantum Hall regime, while theories have predicted novel features observable at microwave frequencies. The purpose of this thesis is to investigate dynamic responses of the electronic system in graphene in the quantum Hall regime by means of broadband microwave measurements. This research first focuses on fabrication of microwave devices based on graphene, including design and electron-beam lithography of the coplanar waveguide patterns around graphene. In this thesis, two designs of graphene microwave devices are demonstrated, one with graphene located between the center line and a ground plane, and the other with graphene at the center gap of the center line. The latter design is equipped with NiCr resistors to achieve impedance matching. With DC and microwave measurements under low temperature (1.5 K) and high magnetic fields (up to 8 T), we observed quantum oscillationsfrom the two-dimensional electronic systems in graphene. We then built an analytical model in an effort to convert the S-parameters acquired in the microwave measurements into AC conductance.