Please use this identifier to cite or link to this item:
Electronic Transport Properties of Monolayer Graphene and Graphene Ribbons
disordered graphene,monolayer graphene,self-assembled graphene ribbons,variable range hopping,confocal scanning microscopy,boundary scattering,
|Publication Year :||2019|
第一個主題研究在無序石墨烯的電傳輸特性，此實驗使用化學氣相沈積石墨烯(chemical vapor deposition (CVD) graphene)和外延石墨烯(epitaxial graphene)的樣品，因為製程中污染或是石墨烯本身的缺陷而形成的無序石墨，其電傳輸機制可以用變程跳躍variable range hopping (VRH)去解釋，使用resistance curve derivative analysis (RCDA)方法可決定樣品的傳輸機制是屬於Mott VRH或Efros-Shklovskii (E-S) VRH。藉由分析樣品的電性，我們可以區分樣品是否有被污染或是本身具有缺陷。
第二個主題中，藉由改善製程和長晶方法，發現在單層外延石墨烯表面上的污染減少很多，因而可以在樣品中量測到優異的整數霍爾效應。而製程中有使用到王水對樣品做處理，王水的硝酸鍵雖然可以使單層外延石墨烯的載子濃度變低，有利於整數霍爾效應在低磁場被觀察到，但硝酸鍵在石墨烯表面上容易與水或是其他物質結合，所以在空氣中，樣品載子濃度會隨著時間改變，不利於樣品品質的穩定。為了解決這問題，我們利用Parylene C薄膜去封裝保護樣品表面不與空氣接觸，更進一步探討Parylene C封裝石墨烯的影響以及藉由恆溫恆溼機測試去評估維持樣品成效。
Graphene may find promising applications in electronics due to its extraordinary electrical properties. However, graphene generally becomes disordered and its electrical properties are affected by the chemical dopants and residues in the fabrication processes. Accordingly, it is highly desirable to avoid chemical dopants and residues on graphene during the fabrication. This thesis is divided into three parts to discuss the impact of electrical properties with disordered graphene and self-assembled graphene ribbons, and further study the amelioration methods for the fabrications.
The first topic involves the electronic transport properties of disordered graphene. In these experiments, both chemical vapor deposition (CVD) graphene and epitaxial graphene (EG) samples are used. The mechanism of electric transport with disordered graphene from chemical dopants in fabrications or the defects is explicated by variable range hopping (VRH) model. By the resistance curve derivative analysis (RCDA), this behavior can be further referred to the Mott VRH or Efros-Shklovskii (E-S) VRH. Accordingly, we can determine whether the samples are doped or have defects with analyzing electronic transport properties of samples.
In the second topic, we improve fabrication processes and the method of growth graphene, and the contamination or defects on monolayer EG are dramatically diminished. Thus, the remarkable integer quantum Hall effect (IQHE) in these samples can be observed. In our fabrication, dilute aqua regia (DAR) is used. In this case, the nitric acid of the DAR may dope graphene. Though the effect of the nitric acid can reduce the carrier density of the samples which allows us to observe the IQHE in the low-magnetic-field regime, the nitric acid may absorb H2O or other chemicals in ambient air makes graphene become p-doped with time. It is disadvantageous to keep the quality of IQHE. To solve this problem, we cover graphene samples with Parylene C to prevent the samples from exposing to ambient air. After that, we further study the effect of Parylene C encapsulation on graphene and the assessment of protecting ability with thermotron tests.
The last topic presents that the electronic transport properties is dependent on the width of samples. In general processes, narrow graphene samples are fabricated by the electron-beam (e-beam) lithography and conventional reactive ion etching (RIE) processes. Though our fabrication process can keep the surface low-dopants, the edges of samples still become nonuniform and doped by e-beam lithography processes and the resist. It has been shown that the edge properties play an important role in transport properties in sufficiently narrow ribbons. The high possibility of back-scattering from nonuniform and doped edges influences electronic transport properties of graphene. In this topic, we use self-assembled graphene ribbons which are prepared by a high-temperature sublimation technique on SiC instead of conventional etched ribbons, and efficient confocal laser scanning microscopy (CLSM) characterization is used for choosing and locating graphene ribbons to make samples. The experimental results describe that the boundary scattering exists due to decreasing the possibility of back-scattering on the smooth and clean edges of a self-assembled graphene ribbon. Accordingly, our high-quality, self-assembled graphene ribbons which guarantee cleaner and more uniform edges may find promising applications in micro-electronics.
|Appears in Collections:||應用物理研究所|
Files in This Item:
|16.52 MB||Adobe PDF|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.