Cs/O沉积Na<sub>2</sub>KSb光电阴极表面的第一性原理研究

王麒铭; 张益军; 王兴超; 王亮; 金睦淳; 任玲; 刘晓荣; 钱芸生

doi:10.7498/aps.73.20231561

摘要

Na₂KSb光电阴极在光电倍增管、图像增强器、真空电子源等领域具有重要应用. 为指导高灵敏度Na₂KSb光电阴极的制备, 采用第一性原理计算方法, 研究不同表面取向和原子终止面的Na₂KSb表面模型, 获得稳定且最有利于电子发射的表面结构. 基于该表面进一步研究了不同覆盖度下的Cs原子沉积和Cs/O原子共沉积对Na₂KSb表面电子结构和光学性质的影响. 对比表面能、吸附能和吸附前后的功函数结果表明, Na₂KSb (111) K表面具有优越的电子发射能力以及良好的稳定性. 当Na₂KSb (111) K表面吸附2/4单层的Cs原子和1/4单层O原子时, 获得最大功函数下降量0.16 eV. 表面吸附Cs/O原子有利于电荷往表面上方转移, 并产生电荷累积, 能形成有效表面偶极矩. 通过分析能带结构和态密度, 发现吸附Cs原子对导带底存在额外的能带贡献, 且引入O原子吸附后价带发生上移. 此外, 吸附Cs/O原子有利于增强表面近红外光吸收, 但是会导致表面紫外和可见光吸收变差.

关键词:

Abstract

Na₂KSb photocathodes have many applications in vacuum optoelectronic devices, such as photomultiplier tubes, image intensifiers, and streak image tubes for high-speed detection and imaging in extremely weak light environments, due to their advantages of high temperature resistance, small dark current, low vacuum requirement, low fabrication cost and high fabrication flexibility. In addition, this type of photocathode has important application prospect in high brightness accelerator photoinjectors. To guide the fabrication of high-sensitivity Na₂KSb photocathodes, Na₂KSb surfaces with different surface orientations and atom terminations are investigated by the first-principles calculation method based on the density functional theory to obtain the most stable and most favorable surface for electron emission. From the perspectives of surface energy, adsorption energy, and work function before and after Cs adsorption, it is revealed that the Na₂KSb (111) K surface exhibits superior surface stability and electron emission capability. Furthermore, the electronic structure and optical properties of Cs adsorption and Cs/O co-adsorption on the Na₂KSb (111) K surface under different Cs coverages are analyzed, and the mechanism of Cs/O deposition on Na₂KSb surface is studied. The adsorption energy of Cs in the Cs/O adsorption model is much larger than that in the single Cs adsorption model, indicating that the adsorption of O atoms on the Na₂KSb surface can make the adsorption of Cs atoms on the surface stronger, and thus increasing the adhesion of Cs atoms on the surface. After adsorption of Cs on the Na₂KSb (111)K surface, the surface work function only decreases by 0.02 eV, while the maximum work function decrease for the Cs/O adsorbed surface is 0.16 eV, with the Cs coverage of 2/4 ML and the O coverage of 1/4 ML. The adsorption of Cs/O atoms on the surface facilitates the charge transfer above the surface and results in charge accumulation, which can form the effective surface dipole moment. The magnitude of the surface dipole moment is directly related to the change of work function. Furthermore, through the analysis of the electronic band structure and density of states, it is found that the adsorbed Cs atoms have additional contribution to the band structure near the conduction band minimum. After the introduction of O atoms, the valence band moves up, also the bottom of the conduction band and the top of the valence band become flat. The Cs/O deposition is beneficial to increasing the absorption of near-infrared light on the Na₂KSb surface, but it will reduce the absorption of ultraviolet light and visible light, and the refractive index will also decrease. This work has a certain reference significance for understanding the optimal emission surface of Na₂KSb photocathode and the mechanism of surface Cs/O deposition.

Keywords:

作者及机构信息

1.
南京理工大学电子工程与光电技术学院, 南京　210094

2.
北方夜视科技(南京)研究院有限公司, 南京　211106

通信作者: 张益军, zhangyijun423@126.com ; 钱芸生, yshqian@njust.edu.cn

基金项目: 国家自然科学基金(批准号: 62271259, U2141239)和国家重大科学仪器设备开发专项(批准号: 2016YFF0100400)资助的课题.

Authors and contacts

1.
School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China

2.
North Night Vision Technology (Nanjing) Research Institute Co., Ltd, Nanjing 211106, China

Corresponding author: Zhang Yi-Jun, zhangyijun423@126.com ; Qian Yun-Sheng, yshqian@njust.edu.cn

Funds: Project supported by the National Natural Science Foundation of China (Grant Nos. 62271259, U2141239) and the Special Funds of the Major Scientific Instruments and Equipment Development of China (Grant No. 2016YFF0100400).

文章全文 : translate this paragraph

参考文献

[1]	Hamamatsu Photonics K. K. https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/etd/PMT_handbook_v4E.pdf [2023-6-1]
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施引文献

图 1 不同Na₂KSb表面模型的表面能和功函数

Fig. 1. Surface energy and work function of different Na₂KSb surface models.

下载: 全尺寸图片幻灯片

图 2 (a) Na₂KSb (111) K表面的Cs, O原子吸附位; (b) 不同Cs/O覆盖度的吸附表面模型; (c) 不同吸附模型的总能量; (d) 不同吸附模型的Cs吸附能

Fig. 2. (a) Adsorption sites for Cs atoms and O atoms on Na₂KSb (111) K surface; (b) adsorption surface models with different Cs/O coverages; (c) the total energies of different adsorption models; (d) the adsorption energies of isolated Cs atom of different adsorption models.

下载: 全尺寸图片幻灯片

图 3 Na₂KSb (111) K表面Cs吸附和Cs/O吸附前后的 (a) Hartree静电势和 (b) 功函数和亲和势

Fig. 3. (a) Hartree electrostatic potential and (b) work function and electron affinity for the Na₂KSb (111) K surfaces before and after adsorption of Cs and Cs/O.

下载: 全尺寸图片幻灯片

图 4 CDD俯视图和侧视图(蓝色和黄色区域分别代表电荷的积累和耗尽)

Fig. 4. Top and side views of CDD (the blue and yellow regions represent the charge accumulation and charge depletion, respectively).

下载: 全尺寸图片幻灯片

图 5 (a) 平均偶极子电荷量变化; (b) 平均偶极子长度变化; (c) 表面偶极矩和功函数变化

Fig. 5. (a) Changes of average dipole charge; (b) changes of the average dipole length; (c) changes of surface dipole moment and work function.

下载: 全尺寸图片幻灯片

图 6 (a) 清洁表面能带结构; (b) Cs覆盖表面能带结构(Cs覆盖度: 2/4 ML, 紫红色曲线表示Cs吸附产生的能带贡献); (c) Cs覆盖表面的Cs原子6s轨道PDOS; (d) Cs/O覆盖表面能带结构(Cs覆盖度: 2/4 ML, O覆盖度: 1/4 ML, 紫红色曲线表示Cs/O吸附产生的能带贡献); (e) Cs/O覆盖表面的Cs原子6s轨道PDOS; (f) Cs/O覆盖表面的O原子2p轨道PDOS

Fig. 6. (a) Band structure for clean surface; (b) band structure for Cs-covered surface (Cs coverage: 2/4 ML, the magenta curve represents the energy band contribution from Cs adsorption); (c) PDOS of the 6s orbit of Cs atoms on the Cs-covered surface; (d) band structure for Cs/O-covered surface (Cs coverage: 2/4 ML, O coverage: 1/4 ML, the magenta curve represents the energy band contribution from Cs/O adsorption); (e) PDOS of the 6s orbit of Cs atoms on the Cs/O-covered surface; (f) PDOS of 2p orbit of O atom on the Cs/O-covered surface.

下载: 全尺寸图片幻灯片

图 7 不同Cs覆盖度下表面模型的光学性质　(a) 折射率; (b) 消光系数

Fig. 7. Optical properties of adsorption surface models with different Cs coverages: (a) Refractive index; (b) extinction coefficient.

下载: 全尺寸图片幻灯片

[1]	Hamamatsu Photonics K. K. https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/etd/PMT_handbook_v4E.pdf [2023-6-1]
[2]	Trucchi D M, Melosh N A 2017 MRS Bull. 42 488 Google Scholar
[3]	田丽萍, 李立立, 温文龙, 王兴, 陈萍, 卢裕, 王俊锋, 赵卫, 田进寿 2018 物理学报 67 188501 Google Scholar Tian L P, Li L L, Wen W L, Wang X, Chen P, Lu Y, Wang J F, Zhao W, Tian J S 2018 Acta Phys. Sin. 67 188501 Google Scholar
[4]	Maxson J, Cultrera L, Gulliford C, Bazarov I 2015 Appl. Phys. Lett. 106 234102 Google Scholar
[5]	Wang Y, Mamun M A, Adderley P, et al. 2020 Phys. Rev. Accel. Beams 23 103401 Google Scholar
[6]	Cultrera L, Gulliford C, Bartnik A, Lee H, Bazarov I 2016 Appl. Phys Lett. 108 134105 Google Scholar
[7]	Yang B 1989 Appl. Phys Lett. 54 2548 Google Scholar
[8]	Rusetsky V S, Golyashov V A, Eremeev S V, et al. 2022 Phys. Rev. Lett. 129 166802 Google Scholar
[9]	Erjavec B 1994 Vacuum 45 617 Google Scholar
[10]	Galan L, Bates Jr C W 1981 J. Phys. D: Appl. Phys. 14 293
[11]	Dolizy P 1980 Vacuum 30 489 Google Scholar
[12]	McCarroll W H, Paff R J, Sommer A H 1971 J. Appl. Phys. 42 569 Google Scholar
[13]	Erjavec B 1996 Appl. Surf. Sci. 103 343 Google Scholar
[14]	Guo T L, Gao H R 1991 Appl. Phys. Lett. 58 1757 Google Scholar
[15]	Guo T L, Gao H R 1993 Appl. Surf. Sci. 70 355
[16]	Guo T L 1996 Thin Solid Films 281 379
[17]	Cultrera L, Karkare S, Lillard B, et al. 2013 Appl. Phys Lett. 103 103504 Google Scholar
[18]	Cultrera L, Lee H, Bazarov I 2016 J. Vac. Sci. Technol. , B 34 011202 Google Scholar
[19]	Ettema A R H F, Groot R A 2000 Phys. Rev. B 61 10035 Google Scholar
[20]	Murtaza G, Ullah M, Ullah N, Rani M, et al. 2016 Bull. Mater. Sci. 39 1581 Google Scholar
[21]	Amador R, Saßnick H D, Cocchi C 2021 J. Phys. Condens. Matter 33 365502 Google Scholar
[22]	Schier R, Saßnick H D, Cocchi C 2022 Phys. Rev. Mater. 6 125001 Google Scholar
[23]	Wang X C, Zhang K M, Jin M C, Ren L, Han Y F, Wang Q L, Zhang Y J 2022 Solid State Commun. 356 114960 Google Scholar
[24]	Wang G X, Pandey R, Moody N A, Batista E R 2017 J. Phys. Chem. C 121 8399
[25]	Shen Y, Yang X D, Bian Y, Chen L, Tang K, Wan J G, Zhang R, Zheng Y D, Gu S L 2018 Appl. Surf. Sci. 457 150 Google Scholar
[26]	向世明, 倪国强 1999 光电子成像器件原理 (北京: 国防工业出版社) 第291页 Xiang S M, Ni G Q 1999 The Principle of Optoelectronic Imaging Devices (Beijing: National Defense Industry Press) p291
[27]	Karkare S, Boulet L, Singh A, Hennig R, Bazarov I 2015 Phys. Rev. B 91 035408 Google Scholar
[28]	Shaltaf R, Mete E, Ellialtioglu S, 2005 Phys. Rev. B 72 205415 Google Scholar
[29]	Hogan C, Paget D, Garreau Y, Sauvage M, Onida G, Reining L, Chiaradia P, Corradini V 2003 Phys. Rev. B 68 205313 Google Scholar

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Cs/O沉积Na₂KSb光电阴极表面的第一性原理研究