石墨烯穿隧結與氧化石墨在高場下電性研究

Abstract

石墨烯穿隧結與氧化石墨在高場下電性研究

學生:蔡崴宇 指導教授:簡紋濱

國立交通大學電子物理所碩士班 摘要 本實驗主要有三個部份，分別是石墨烯穿隧元件的量測、石墨烯高場下電性的量測及氧化石墨高場下電性的量測。 石墨烯穿隧元件，在石墨烯上鍍一絕緣層氧化鋁來製作穿隧結元件，反覆試驗氧化鋁的鍍率與厚度，可達最佳穿隧結效果，將穿隧電流與電壓的關係轉換成微分電導對電壓的關係，藉此探索石墨烯的能態密度與電子結構，其結果與文獻中石墨烯的能態密度報導相符合。此外，在石墨烯表面鍍上一高分子層，想藉由石墨烯元件來測量此高分子的能態密度，在0.7 V觀察到電子態震盪起伏，此電子態接近用伏安法測得的氧化還原電位接近。 在石墨烯高場量測方面，利用背電極調整石墨烯化學位能到狄拉克點上，來觀察Schwinger預測的電子正子產生機制，Schwinger預測中在高電場下，二維材料的電流密度會與電場的1.5次方成正比，本實驗因電場無法增加到105 m/s以上，只能觀察到電流密度與電場呈現線性相關，最後在大電場下，石墨烯無法承受大電流而燒毀。 為了在材料中觀察到Schwinger pair creation，採用長庚大學孫嘉良教授實驗室所提供的氧化石墨，這次的結果在低電場的部分，電流密度與電場關係，符合了線性的歐姆定律，而高電場下，電流密度隨電場變化符合了Schwinger的預測，表現出非線性關係，且隨著電場的二次方而變化。

Tunneling junction on pure graphene and high field electron transport in graphite oxide

Student: Wei-Yu Tsai Advisor: Prof. Wen-Bin Jian

Institute of Electrophysics National Chiao Tung University

Abstract There are three parts in this thesis. It consists of tunneling junction in pure graphene, high field electron transport in pure graphene, and high field electron transport in graphite oxide. In the first part, the aluminum oxide with the optimal deposition rate and thickness is used as an insulator for making tunneling junctions. After we made the devices, we measure the differential current to study the density of state of pure graphene. Our results of density of states are in agreement with those in previous reports. Additionally, we deposited some organic molecules and tried to check the density of states of molecules by using the devices of graphene tunneling junction. We observed an additional peak at +0.7 V that could be related to the electronic structure of the molecules on surface. The peak position is very close to that observed in the cyclic voltammetry measurements. The second part of the thesis introduces the high field electron transport in pure graphene. In the experiments, we gated the chemical potential of the pure graphene to the Dirac point for the observation of Schwinger mechanism. It is a pity that the graphene devices broke down in a high electric field of ~105 V/m. For a lower electric field, we did not see any power law J-E behavior with the exponent of 1.5. We only observed the linear J-E behavior that indicates the Ohm's law behavior of electron transport in pure graphene in the low electric field. On the other hand, we alternatively selected graphite oxides which were synthesized in Prof. Chia-Liang Sun’s group in Chang Gung University. This material unexpectedly showed good result. The J-E behavior shows a linear relation (Ohm's law) in low field and a power-law, nonlinear relation in high field. The J-E curves in high field agree with Schwinger’s theory. The power law with an exponent of ~2 is very close to the theoretical calculation in a three-dimensional system.