探討不同層數熱還原氧化石墨烯 材料的電性

在平面結構材料石墨烯於2010年得到諾貝爾獎後，石墨烯至石墨塊材性質上的演變也備受關注，過去石墨烯層數的判別主要採取原子力顯微鏡和拉曼光譜兩種方式，本實驗則試圖以穿隧電導和變溫電阻率兩種電性量測作為判斷真實層數的方式，更進一步了解石墨烯演變成石墨塊材過程中多項物理特性對傳輸性質所造成的影響。本實驗先以原子力顯微鏡測量熱還原氧化石墨烯相對基板的厚度並換算成實際層數，再以電子束微影及熱蒸鍍和濺鍍等技術製作厚度8 奈米的氧化鋁穿隧元件。量測不同層數熱還原氧化石墨烯在不同溫度下(30K~300K)的電阻率，發現量測結果符合簡單雙能帶STB及變程跳躍VRH理論，其中的參數可驗證過去實驗和理論計算的結果：當層數增加時載子等效質量隨之增加，聲子電子交互作用強度隨之增強，導電帶和價電帶重疊能量範圍趨於定值，能態密度隨之增加。其次量測不同偏壓下的穿隧電導，由單層石墨烯能態密度隨偏壓絕對值加大而增大且於偏壓絕對值大於2V之後增大程度更加劇烈的結果可了解π和σ能帶對能態密度的共同貢獻，另外不同層數石墨烯能態密度隨層數增加而增加，在零偏壓下多層石墨烯與單層石墨烯能態密度的比值正好與彼此層數的比值相近且幾何尺度歸一化後的能態密度和價電帶導電帶能量重疊範圍趨勢接近。以上藉由實驗加上理論的說明能對不同層數石墨烯的能態密度及能帶結構等物理特性有更多的了解。

關鍵字

石墨烯

並列摘要

The unique electrical properties of a real two-dimensional material, graphene, have attracted a lot of attentions since it was realized in 2004. The evolution from graphite to graphene has also been an interesting subject. Atomic force microscopy (AFM) and Raman spectrum have been, so far, the only two standard methods to identify layer number of the few-layer graphene (FLG). In this study, we use two different methods of electrical measurement for the determination of the layer number of FLG. We have observed a variation of resistivity at different temperature and conductivity at different bias voltage, and have investigated changes of physical properties with an increase of the layer number. Before the device fabrication, AFM is used to measure the thickness of the FLG for the estimation of the layer number. We use electron-beam lithography to make two types of devices for different electrical measurements. Type I devices are purely Ohmic-contacted devices. The metal electrodes are made by radio-frequency sputtering deposition. Type II devices are tunneling devices with a 8-nm thick aluminum oxide layer between metal (platinum) electrodes and a FLG. Resistivities of Type I devices are measured in the temperature range from 300 K to 30 K and the data are analyzed in accordance with the simple two band (STB) model. The layer dependent properties have been extracted through our analyses. When the layer number increases, the effective carrier mass, the electron-phonon interaction, and the density of state at Fermi level increase whereas the band overlap is kept constant. By analyzing our data from electrical measurements with the theoretical model, we have discovered alternatively other physical parameters which dependent strongly on the layer number of the FLG.

並列關鍵字

graphene

參考文獻

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探討不同層數熱還原氧化石墨烯材料的電性

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