Max Planck Institute for Polymer Research , 55128 Mainz, Germany.
Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute , Troy, 12180 New York, United States.
ACS Nano. 2017 Feb 28;11(2):1380-1388. doi: 10.1021/acsnano.6b06405. Epub 2017 Feb 1.
The bottom-up approach to synthesize graphene nanoribbons strives not only to introduce a band gap into the electronic structure of graphene but also to accurately tune its value by designing both the width and edge structure of the ribbons with atomic precision. We report the synthesis of an armchair graphene nanoribbon with a width of nine carbon atoms on Au(111) through surface-assisted aryl-aryl coupling and subsequent cyclodehydrogenation of a properly chosen molecular precursor. By combining high-resolution atomic force microscopy, scanning tunneling microscopy, and Raman spectroscopy, we demonstrate that the atomic structure of the fabricated ribbons is exactly as designed. Angle-resolved photoemission spectroscopy and Fourier-transformed scanning tunneling spectroscopy reveal an electronic band gap of 1.4 eV and effective masses of ≈0.1 m for both electrons and holes, constituting a substantial improvement over previous efforts toward the development of transistor applications. We use ab initio calculations to gain insight into the dependence of the Raman spectra on excitation wavelength as well as to rationalize the symmetry-dependent contribution of the ribbons' electronic states to the tunneling current. We propose a simple rule for the visibility of frontier electronic bands of armchair graphene nanoribbons in scanning tunneling spectroscopy.
采用自下而上的方法合成石墨烯纳米带不仅旨在为石墨烯的电子结构引入带隙，而且还通过以原子精度设计纳米带的宽度和边缘结构来精确调整其值。我们通过表面辅助芳基-芳基偶联以及随后对适当选择的分子前体进行环脱氢反应，在 Au(111)上合成了宽度为九个碳原子的扶手椅型石墨烯纳米带。通过结合高分辨率原子力显微镜、扫描隧道显微镜和拉曼光谱，我们证明了所制造的纳米带的原子结构完全符合设计。角分辨光电子能谱和傅里叶变换扫描隧道光谱揭示了 1.4 eV 的电子带隙和约为 0.1 m 的电子和空穴的有效质量，这与开发晶体管应用的先前努力相比有了实质性的提高。我们使用从头算计算深入了解拉曼光谱对激发波长的依赖性，以及合理解释纳米带电子态对隧道电流的对称依赖性贡献。我们提出了一个简单的规则，用于解释在扫描隧道光谱中扶手椅型石墨烯纳米带的前沿电子带的可见性。
