Abstract
Through alternate activation, the surface of GaN nanowires can be made more stable. Three alternate activation methods of Cs/O/Cs, Cs/NF3/Cs, Cs/Li/NF3/Cs/Li were used to activate the p-type surface of GaN nanowires. The results show that the multiple activation method can make the Cs atom not easy to desorb. Cs/NF3 alternative activation is simple and feasible. The best coverage ratio of Cs, O atoms (NF3 molecules) in the first process and Cs in the second process is 3:1(2):4. Cs and NF3 molecules can form a stronger connection. The incorporation of auxiliary substances (Li, O atoms, and NF3 molecules) also helps to improve the adhesion of the main activated atoms such as Cs atoms. Li atoms, O atoms, and NF3 molecules are closer to the GaN nanowires.
Impact statement
NEA surface is a key step in the preparation process of photoemission materials. For the reveal of the formation mechanism of NEA of GaN nanowires, the work function, the relaxed atomic structure, optoelectronics performances of GaN nanowires during the alternate activation of Cs/O/Cs, Cs/NF3/Cs, and Cs/Li/NF3/Cs/Li are investigated based on the first principles. The best coverage ratio of Cs, O atoms (NF3 molecules) in the first process and Cs in the second process is 3:1(2):4. The ratio of Li atoms is the same as that of Cs atoms. Compared with O atoms, Cs and NF3 molecules can form a stronger connection. Li atoms, O atoms, and NF3 molecules are almost in the encircling circle of Cs atoms, which are closer to the GaN nanowires. The co-adsorption of multiple activating substances makes the band structure on the surface of the nanowire show metallic characteristics, and the absorption peak also shifts to a place where the photon energy is lower. The optimal ratio of activated atoms and molecules is determined. It is believed that our research could contribute to the progress and development of the NEA photocathode.
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The raw/processed data required to reproduce these findings cannot be shared at this time as the data also form part of an ongoing study.
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Acknowledgments
This work is supported by the Natural Science Foundation of Jiangsu Province-China (Grant No. BK20211193) and LLL Night Vision Technology Key Laboratory Fund (Grant No. J20210103). M. Wang of Ludong University is greatly appreciated for the help of first-principles calculations.
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Lu, F., Liu, L. & Tian, J. Surface stability of GaN nanowires under Cs/O/Cs, Cs/NF3/Cs, Cs/Li/NF3/Cs/Li-activated conditions based on first principles. MRS Bulletin 47, 906–912 (2022). https://doi.org/10.1557/s43577-022-00319-0
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DOI: https://doi.org/10.1557/s43577-022-00319-0