Schaber Jana, Xiang Rong, Teichert Jochen, Arnold André, Murcek Petr, Zwartek Paul, Ryzhov Anton, Ma Shuai, Gatzmaga Stefan, Michel Peter, Gaponik Nikolai
SRF-Gun Group, ELBE Department, Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany.
Eychmüller Group, Institute of Physical Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.
Micromachines (Basel). 2022 May 29;13(6):849. doi: 10.3390/mi13060849.
Accelerator scientists have high demands on photocathodes possessing high quantum efficiency (QE) and long operational lifetime. p-GaN, as a new photocathode type, has recently gained more and more interest because of its ability to form a negative electron affinity (NEA) surface. Being activated with a thin layer of cesium, p-GaN:Cs photocathodes promise higher QE and better stability than the known photocathodes. In our study, p-GaN samples grown on sapphire or silicon were wet chemically cleaned and transferred into an ultra-high vacuum (UHV) chamber, where they underwent a subsequent thermal cleaning. The cleaned p-GaN samples were activated with cesium to obtain p-GaN:Cs photocathodes, and their performance was monitored with respect to their quality, especially their QE and storage lifetime. The surface topography and morphology were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX) spectroscopy. We have shown that p-GaN could be efficiently reactivated with cesium several times. This paper systematically compares the influence of wet chemical cleaning as well as thermal cleaning at various temperatures on the QE, storage lifetime and surface morphology of p-GaN. As expected, the cleaning strongly influences the cathodes' quality. We show that high QE and long storage lifetime are achievable at lower cleaning temperatures in our UHV chamber.
加速器科学家对具有高量子效率（QE）和长工作寿命的光阴极有很高的要求。p型氮化镓（p-GaN）作为一种新型光阴极，由于其能够形成负电子亲和势（NEA）表面，最近越来越受到关注。用一层薄铯激活后，p-GaN:Cs光阴极有望比已知的光阴极具有更高的量子效率和更好的稳定性。在我们的研究中，在蓝宝石或硅上生长的p-GaN样品经过湿法化学清洗后转移到超高真空（UHV）腔室中，在那里进行后续的热清洗。清洗后的p-GaN样品用铯激活以获得p-GaN:Cs光阴极，并对其性能进行监测，特别是量子效率和存储寿命方面。通过原子力显微镜（AFM）、扫描电子显微镜（SEM）结合能量色散X射线（EDX）光谱对表面形貌和形态进行了检测。我们已经表明，p-GaN可以用铯多次有效地重新激活。本文系统地比较了湿法化学清洗以及不同温度下的热清洗对p-GaN的量子效率、存储寿命和表面形貌的影响。正如预期的那样，清洗对阴极质量有很大影响。我们表明，在我们的超高真空腔室中，较低的清洗温度下可以实现高量子效率和长存储寿命。
