Influence of air exposure on CsI photocathodes

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• 作者：Yuguang Xie ; Aiwu Zhang ; Yingbiao Liu ; Hongbang Liu ; Tao Hu ; Li Zhou ; Xiao Cai ; Jian Fang ; Boxiang Yu ; Yongshuai Ge ; Qiwen L¨¹ ; Xilei Sun ; Lijun Sun ; Zheng Xue ; Yigang Xie ; Yangheng Zheng ; Junguang L¨¹
• 关键词：CsI photocathode ; Air exposure ; Quantum efficiency ; Surface morphology ; XPS
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2012
• 出版时间：11 October, 2012
• 年：2012
• 卷：689
• 期：Complete
• 页码：79-86
• 全文大小：1053 K

文摘

We investigate the influence of air exposure on the quantum efficiency (QE) and surface morphology of CsI photocathodes (PCs), at relative humidities (RH) higher than 80 % down to nearly 3 % (both at room temperature) and a 60 ¡ãC baking condition. By atomic force microscopy (AFM) surface analysis, it is clearly seen that RH speeds up water film formation and CsI dissolution on the surface of the photocathode at the minute scale, while both grain size and QE change slowly at RH at the hour scale. In the baking environment, the peak QE decreases less than 1.5 % (absolute) within one week, and a stainless steel substrate and electron beam evaporation technique tend to effectively weaken the influence of air. With an Au-coated FR-4 substrate, the QE degradation is found to strongly depend on wavelength in the range of 120-210 nm. According to spectra of X-ray photoelectron spectroscopy (XPS), an excess of cesium was observed and the chemical reaction between water and CsI when exposed to humid air is proved. It is found that carbon, and not H₂O or O₂, is the main pollutant in the baking condition.