Cs/O沉积Na_(2)KSb光电阴极表面的第一性原理研究  

First-principles study of Cs/O deposited Na_(2)KSb photocathode surface

作　　者：王麒铭 张益军[1] 王兴超 王亮 金睦淳 任玲 刘晓荣 钱芸生[1] Wang Qi-Ming;Zhang Yi-Jun;Wang Xing-Chao;Wang Liang;Jin Mu-Chun;Ren Ling;Liu Xiao-Rong;Qian Yun-Sheng(School of Electronic and Optical Engineering,Nanjing University of Science and Technology,Nanjing 210094,China;North Night Vision Technology(Nanjing)Research Institute Co.,Ltd,Nanjing 211106,China)

机构地区：[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

出　　处：《物理学报》2024年第8期341-349,共9页Acta Physica Sinica

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

摘　　要：Na_(2)KSb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Na_(2)KSb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Na_(2)KSb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Na_(2)KSb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,Na_(2)KSb(111)K表面具有优越的电子发射能力以及良好的稳定性.当Na_(2)KSb(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.Na_(2)KSb 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 highsensitivity Na_(2)KSb photocathodes,Na_(2)KSb 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 Na_(2)KSb(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 Na_(2)KSb(111)K surface under different Cs coverages are analyzed,and the mechanism of Cs/O deposition on Na_(2)KSb 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 Na_(2)KSb 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 Na_(2)KSb(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

关 键 词：Na_(2)KSb 光电阴极 Cs/O沉积 功函数 偶极矩 

分 类 号：O469[理学—凝聚态物理]