Quantum Efficiency Lifetime Studies using the Photocathode Preparation Experimental Facility Developed for the ALICE Accelerator
Quantum Efficiency Lifetime Studies using the Photocathode Preparation Experimental Facility Developed for the ALICE Accelerator
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发表时间：
2012-01
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通讯作者：
N. Chanlek
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作者：
N. Chanlek
本论文描述了一个砷化镓光电阴极制备设备（PPF）的发展与负载锁定接口的升级ALICE光注入电子枪的一部分。PPF能够制备多达六个负电子亲和力（NEA）GaAs光阴极，并允许快速、可靠地更换枪中退化的光阴极，同时保持枪真空系统的完整性。本文利用自制的表面表征系统，结合几种表面科学表征技术，在同一真空系统中，对NEA GaAs光电阴极的制备进行了研究和开发。利用与半导体物理研究所（ISP/新西伯利亚）合作设计和开发的GaAs/AlGaAs异质结构光电阴极，以可再现的方式实现了635 nm处15 - 19%的量子效率（QE）和6，800小时量级的长寿命。使用的PPF，我已经调查了NEA GaAs光电阴极的QE的退化下暴露于气体通常存在于枪真空，即O2，CO2，CO，H2，CH 4和N2。首次在基压为10 E-11 mbar的真空装置中证实了这些气体对NEA GaAs光电阴极的影响。结果发现，H2，CH 4和N2的光阴极寿命上没有影响，而大量减少的QE已观察到在暴露于O2，CO2和CO。它也首次证明，NEA GaAs光阴极激活Cs和NF 3是更稳定的CO2和CO曝光过程中比光阴极激活Cs和O2。
This thesis describes the development of a gallium arsenide (GaAs) photocathode preparation facility (PPF) with a load-lock interface as part of an upgrade to the ALICE photo-injector electron gun. The PPF has the capacity to prepare up to six negative electron affinity (NEA) GaAs photocathodes, and permits the rapid and reliable replacement of the degraded photocathode in the gun, while maintaining the integrity of the gun vacuum system. The photocathode preparation has been studied and developed using a custum-built surface characterisation system which permitsthe preparation of NEA GaAs photocathode in conjunction with the application ofseveral surface science characterisation techniques within the same vacuum system. With GaAs/AlGaAs hetero-structure photocathodes designed and developed in collaboration with the Institute of Semiconductor Physics (ISP/Novosibirsk), quantum efficiencies (QE) of 15 - 19% at 635 nm and long lifetimes of the order of 6,800 hours are achieved in a reproducible way. Using the PPF, I have investigated the degradation in the QE of NEA GaAs photocathodes under exposures to gases typically present in the gun vacuum, namely O2, CO2, CO, H2, CH4 and N2. The effects of these gases on the NEA GaAs photocathodes have been demonstrated for the firrst time in a vacuum set-up with a base pressure in 10E-11 mbar range. It was found that H2, CH4 and N2 have no effect on the photocathodes lifetime, whilst substantial reductions of the QE have been observed during the exposures to O2, CO2 and CO. It was also demonstrated for the first time that the NEA GaAs photocathode activated with Cs and NF3 is more stable during CO2 and CO exposures than the photocathode activated with Cs and O2.