EELS and Optical Properties of Layered and 2D Materials

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• Shangpeng Gao
• Wednesday 31 July 2024, 14:00-15:30
• TCM Seminar Room.

If you have a question about this talk, please contact Bo Peng.

I will start by reviewing our recent work applying electron energy-loss spectroscopy (EELS) simulations to materials characterization and electronic structure research. By combining experimental (S)TEM-EELS with simulations, we mapped the electronic states attributed to specific unoccupied pz orbitals around a fourfold-coordinated silicon point defect in graphene [1] and confirmed the existence of a new layered hexagonal crystal: h-BeO [2]. Our study reveals the unusual bonding characteristics of fivefold-coordinated structures (h-AlN and h-MgO) with planar AB honeycombs, highlighting a “missing π” character [3].

Next, I will introduce an effective method to accurately predict the dielectric and optical properties of 2D materials by restoring their intrinsic dielectric functions independently of the additional vacuum spacing employed in supercell calculations. Using this method, we evaluated the momentum- and thickness-dependent excitonic and plasmonic properties of 2D h-BN and MoS2 [4,5].

Lastly, I will demonstrate how DFT calculations of stress-dependent formation energies and migration energies of vacancies and self-interstitials can aid in growing perfect single-crystal silicon ingots for the semiconductor industry [6].

References:

[1] M. Q. Xu, A. W. Li, S. J. Pennycook, S. P. Gao, W. Zhou. Physical Review Letters 131: 186202 (2023)

[2] L. F. Wang, L. Liu, J. Chen, et al. Angewandte Chemie International Edition 59(36): 15734–15740 (2020)

[3] A. A. Sun, S. P. Gao, G. Gu. Chemical Science 11(17): 4340-4350 (2020)

[4] G. Yang, S. P. Gao. Nanoscale 13: 17057 (2021)

[5] G. Yang, J. C. Fan, S. P. Gao. Nanoscale Advances 5: 6990–6998 (2023)

[6] H. J. Hu, Z. R. He, Y. Pei, et al. Crystal Growth & Design. In press. https://doi.org/10.1021/acs.cgd.4c00164

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