Opening an Electrical Band Gap of Bilayer Graphene with Molecular Doping

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• 作者：Wenjing Zhang ; Cheng-Te Lin ; Keng-Ku Liu ; Teddy Tite ; Ching-Yuan Su ; Chung-Huai Chang ; Yi-Hsien Lee ; Chih-Wei Chu ; Kung-Hwa Wei ; Jer-Lai Kuo ; Lain-Jong Li
• 刊名：ACS Nano
• 出版年：2011
• 出版时间：September 27, 2011
• 年：2011
• 卷：5
• 期：9
• 页码：7517-7524
• 全文大小：1010K
• 年卷期：0
• ISSN：1936-086X

文摘

The opening of an electrical band gap in graphene is crucial for its application for logic circuits. Recent studies have shown that an energy gap in Bernal-stacked bilayer graphene can be generated by applying an electric displacement field. Molecular doping has also been proposed to open the electrical gap of bilayer graphene by breaking either in-plane symmetry or inversion symmetry; however, no direct observation of an electrical gap has been reported. Here we discover that the organic molecule triazine is able to form a uniform thin coating on the top surface of a bilayer graphene, which efficiently blocks the accessible doping sites and prevents ambient p-doping on the top layer. The charge distribution asymmetry between the top and bottom layers can then be enhanced simply by increasing the p-doping from oxygen/moisture to the bottom layer. The on/off current ratio for a bottom-gated bilayer transistor operated in ambient condition is improved by at least 1 order of magnitude. The estimated electrical band gap is up to ∼111 meV at room temperature. The observed electrical band gap dependence on the hole-carrier density increase agrees well with the recent density-functional theory calculations. This research provides a simple method to obtain a graphene bilayer transistor with a moderate on/off current ratio, which can be stably operated in air without the need to use an additional top gate.