Recently, the joint research group led by Peng Gao, Kaihui Liu (Peking University), and Yuyang Zhang from the University of Chinese Academy of Sciences employed transmission electron microscopy with electron energy loss spectroscopy and first-principles calculations, uncovered the twist-angle coupling effect in h-BN/graphene heterostructures.
This work is published in Physical Review Letters, 131, 016201 (2023), with title “Tunable Interband Transitions in Twisted h-BN/Graphene Heterostructures”：https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.016201
Figure 1. Measurement of interband transitions in angular h-BN/graphene heterostructures. (a) Schematic diagram of the STEM-EELS optical configuration. (b-c) Diffraction patterns (b) and HAADF images (c) of h-BN/graphene heterostructures with angles of 5.6°, 10.3°, 15.5°, 21.9°, and 28.2°, respectively. In (c), the scale bar represents 1 nm. (d) EELS spectra of h-BN/graphene heterostructures with different angles. (e) Peak fitting method using Gaussian profiles, demonstrated with the example of the 24° EELS result. (f) Extracted transition energies from (d), with error bars obtained from multiple repeated measurements.
FIG. 2. Energy loss function and Gr-Gr intralayer transition. (a) Calculated energy loss functions of twisted h-BN=Gr heterostructures. (b) Calculated band structure of h-BN=Gr vertical heterostructure with 0°twist angle, in which the pink and blue arrows indicate the first and the second transition pathways, respectively. (c) Comparison of experimental (pink) and DFT-simulated results (gray) of the Gr-Gr transitions in h-BN=Gr heterostructures with different twist angles. (d) Calculated Gr DOS in h-BN=Gr heterostructure with different twist angles, in which the pink and blue shades cover the ranges of DOS peaks in Gr valence and conduction bands, respectively.
FIG. 3. The interlayer transitions S2 and S3. (a) The interacted vs. non-interacted ELF by IPA calculations. (b) The v-band of h-BN and the c-band of Gr closest to the Fermi level. (c) Calculated vertical transition spectra of the twisted h-BN/Gr heterostructures. The 2nd and 3rd transition peaks are marked in blue and green shades. (d) Comparison between the experimental and the calculational results. (e) Vertical transition points in reciprocal space of the 0°, 9°, 24°, and 30° h-BN/ Gr twisted heterostructures. The pink and black hexagons indicate the boundaries of 1-BZ of Gr and h-BN, respectively. The vertical transition points corresponding to the 2nd and 3rd transitions are marked in blue and green ribbons, respectively, and are emphasized by blue and green arrows.
