XPS analysis on multi alkali photocathode
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摘要: 介绍了多碱阴极的特点及其在超二代像增强器中的应用。叙述了多碱阴极进行制作和封接，之后在XPS 分析仪器的预真空室中进行解封并送入仪器分析室进行分析的过程。对多碱阴极不同膜层厚度处各元素原子的百分比进行了XPS 分析。首先对多碱阴极的表面进行宽谱扫描，发现元素之后再针对各个元素进行窄谱扫描，之后进行氩离子刻蚀。刻蚀一定时间后再对多碱阴极表面进行宽谱或窄谱扫描，氩离子刻蚀一直进行到阴极玻璃窗的表面。通过氩离子刻蚀并结合XPS 能谱分析，得出了多碱阴极膜层内部不同厚度处Na 元素、K 元素和Sb 元素的原子百分比。结果表明：多碱阴极的结构是一种两层结构，即以Na2KSb 为基础层，表面再吸附Cs 原子层。两层膜层中，Na2KSb 基础层较厚，而Cs 原子层较薄，厚度仅为整个阴极膜层厚度的2.7%。另外，实测多碱阴极膜层中Na 原子、K 原子和Sb 原子数量的百分比并不完全遵循2：1：1 的化学计量比，并且在整个阴极膜层厚度范围内，三种元素的原子百分比并不保持恒定，未出现在某一位置处三种元素原子百分比达到2：1：1 的理想状态。原因是目前多碱阴极制作工艺对蒸发元素蒸发量的控制精度较低。理论和实践证明，只有获得具有严格化学计量比的Na2KSb 膜层才可能获得高的灵敏度，因此，如果采用分子束外延技术来制作多碱阴极，那么成分控制的精度将大大改善，2：1：1 的化学计量比才可能获得，阴极灵敏度才会得到进一步的提高。Abstract: The characteristics of multi-alkali cathode, making process as well as the application in the second generational image intensifier was introduced, the sealing process between cathodes and envelops was explained, and cathode was fed to pre chamber of XPS analysis instrument. The percentage of atoms of each element in the thickness of different layer of multi alkali cathode was obtained by XPS analysis. First wide spectrum scan on the top surface of multi alkali cathode was made, and then the narrow spectrum scan was made on every element, following by argon ion etching. Etching after a certain time, wide spectrum and narrow spectrum scan on the multi alkali cathode were made;an argon ion etching was carried out until to the interface of glass window. Argon ion etching combined with XPS spectra analysis, atomic percentage of Na elements, K elements and Sb elements was obtained within the multi-alkali cathode film thickness. The results show that the multi-alkali cathode structure is a two-layer structure, i.e. Na2KSb base layer and adsorbed Cs atoms layer. In two film layer, Na2KSb layer is thicker, while the Cs atomic layer is thin, only 2.7% for the entire cathode film thickness. In addition, the number percentage of Na atoms, K atom, Sb atoms does not follow 2:1:1 stoichiometric ratio, and in the entire cathode layer thickness range, the percentage of atoms of the three elements does not remain constant, and does not appear in the ideal state of the atomic percentage of the three elements at a position reached 2:1:1. Theory and practice has proved it is possible to obtain high sensitivity only with strict stoichiometric ratio Na2KSb film. Thus by molecular beam epitaxy, multi-alkali cathode with higher composition control accuracy stoichiometric ratio 2:1:1 could be produced, the higher cathode sensitivity will be obtained.
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Key words:
- multi alkali cathode /
- energy spectrum /
- etching /
- binding energy /
- atom
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