A new attempt to further reduce the work function of the cesiated surface: The strongest electronegative element fluorine co-adsorption with cesium on Mo (001) surface

• Published in: Nuclear materials and energy 2024-12, Vol.41, p.101738, Article 101738
• Main Authors: Li, Heng, Zhang, Xin, Xu, Yuhong, Lei, Guangjiu, Liu, Sanqiu, Cui, Zilin, Hu, Jun, Zhu, Yiqin, Li, Xiaolong, Liu, Xiaoqiao, Zheng, Huaqing, Geng, Shaofei, Chen, Xiaochang, Liu, Haifeng, Wang, Xianqu, Liu, Hai, Tang, Changjian
• Format: Article
• Language: English
• Subjects: Cesiated surface; Dipole moment; Fluorine; Negative ion source; Work function
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2024.101738

•The influence of electronegative element fluorine on the work function of cesiated surface was studied.•It is assumed that cesium and impurity atoms are evenly distributed on the surface, forming a highly symmetrical structure.•Only when the cesium coverage is 0.5ML, fluorine can further reduce the work function.•In order to obtain a lower surface work function, the surface coverage of cesium needs to be precisely controlled. The efficiency of hydrogen negative ion production in negative ion sources depends on the work function of the molybdenum surface. Deposition of cesium (Cs) atoms on the Mo surface reduces the work function from over 4.0 eV to about 1.50–1.80 eV. However, the Fermi level remains below the affinity level (−0.75 eV) of hydrogen negative ions. To explore further reduction methods, the work function of Cs co-adsorbed with fluorine on the Mo (001) surface was studied using DFT calculations. The results show that at 4/16 θ Cs coverage, adding fluorine can reduce the work function, achieving the lowest value of 1.40 eV at 8/16 θ F coverage. Analysis reveals a significant vacuum-inward dipole moment with fluorine-Cs co-adsorption, favorably reducing the work function. However, fluorine’s strong electronegativity also creates a surface-directed dipole moment, increasing the work function. Introducing fluorine is beneficial only at 4/16 θ Cs coverage, indicating that precise control of Cs coverage is necessary to achieve lower work functions.