Research Center for Applied Sciences, Academia Sinica, Taipei, 11529, Taiwan.
ACS Nano. 2011 Sep 27;5(9):7517-24. doi: 10.1021/nn202463g. Epub 2011 Aug 9.
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.
在石墨烯中打开电带隙对于将其应用于逻辑电路至关重要。最近的研究表明，通过施加电位移场可以在伯纳尔堆叠的双层石墨烯中产生能隙。通过打破面内对称或反转对称，分子掺杂也被提出用于打开双层石墨烯的电带隙；然而，尚未报道直接观察到电带隙。在这里，我们发现三嗪有机分子能够在双层石墨烯的顶表面形成均匀的薄涂层，这有效地阻止了可及的掺杂位点，并防止了顶层的环境 p 掺杂。通过简单地增加从氧气/水分到底层的 p 掺杂，就可以增强顶层和底层之间的电荷分布不对称性。在环境条件下运行的底栅双层晶体管的开/关电流比提高了至少 1 个数量级。在室温下，估计的电带隙高达约 111 meV。观察到的电带隙与空穴载流子密度增加的依赖性与最近的密度泛函理论计算非常吻合。这项研究提供了一种简单的方法来获得具有适度开/关电流比的石墨烯双层晶体管，该晶体管可以在空气中稳定运行，而无需使用额外的顶栅。
