Lee Hae Yeon, Al Ezzi Mohammed M, Raghuvanshi Nimisha, Chung Jing Yang, Watanabe Kenji, Taniguchi Takashi, Garaj Slaven, Adam Shaffique, Gradečak Silvija
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02141, United States.
Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore.
Nano Lett. 2021 Apr 14;21(7):2832-2839. doi: 10.1021/acs.nanolett.0c04924. Epub 2021 Feb 16.
Control of materials properties has been the driving force of modern technologies. So far, materials properties have been modulated by their composition, structure, and size. Here, by using cathodoluminescence in a scanning transmission electron microscope, we show that the optical properties of stacked, >100 nm thick hexagonal boron nitride (hBN) films can be continuously tuned by their relative twist angles. Due to the formation of a moiré superlattice between the two interface layers of the twisted films, a new moiré sub-band gap is formed with continuously decreasing magnitude as a function of the twist angle, resulting in tunable luminescence wavelength and intensity increase of >40×. Our results demonstrate that moiré phenomena extend beyond monolayer-based systems and can be preserved in a technologically relevant, bulklike material at room temperature, dominating optical properties of hBN films for applications in medicine, environmental, or information technologies.
材料性能的控制一直是现代技术发展的驱动力。到目前为止，材料性能是通过其成分、结构和尺寸来调节的。在此，我们利用扫描透射电子显微镜中的阴极发光技术表明，堆叠的、厚度大于100 nm的六方氮化硼（hBN）薄膜的光学性能可通过其相对扭转角进行连续调节。由于扭曲薄膜的两个界面层之间形成了莫尔超晶格，随着扭转角的变化，会形成一个新的莫尔子带隙，其幅度不断减小，从而导致发光波长可调，强度增加超过40倍。我们的结果表明，莫尔现象不仅存在于基于单层的系统中，而且在室温下的一种与技术相关的块状材料中也能保留，主导着hBN薄膜在医学、环境或信息技术应用中的光学性能。
