Synthesis, Properties and Characterization of Alkali Antimonide Photocathodes for Next-Generation Photoinjectors

摘要

Alkali antimonide photocathodes, which include K2CsSb and Cs3Sb, have been considered as excellent candidates as the electron source used in a wide range of applications because of their excellent properties including high quantum efficiency (QE), low emittance, good lifetime and fast response. Next-generation photoinjectors, such as energy recovery linacs (ERL) and free electron laser (FEL), require high quality electron beam which could be obtained from a robust alkali antimonide photocathode with high QE and sub-nm roughness. In recent years, synchrotron X-ray has been used as a powerful in-situ technique to understand the growth mechanism of alkali antimonide photocathode. Previous studies have shown that traditional sequential deposition to grow alkali antimonide has its intrinsic drawback which is not reproducible and reliable in achieving high QE, low surface roughness, etc, hence, exploring novel growth methods to synthesize alkali antimonide photocathode with desired properties is in great demand.;In this dissertation, in-situ X-ray characterization study has been performed on bi-alkali antimonide K-Cs-Sb photocathode grown by various recipes, which include the modified sequential deposition, ternary co-evaporation and the sputtering deposition. It has been found that photocathodes with high QE of over 4% at 532-nm wavelength of light and sub-nm rms surface roughness can be obtained by these novel growth recipes, which would be very promising for their application in future photoinjectors.;In addition to the study on the growth recipe, the properties of the photocathode synthesized by pure alkali metal effusion cells are characterized and compared to that by traditional alkali metal dispensers based on our growth system. Using pure alkali effusion sources, alkali antimonide photocathode with high QE, low roughness and strong texture can be reproducibly prepared by the reliable and straightforward two-step recipe, which would significantly facilitate the preparation process of the alkali antimonide photocathode. Results of an approach to prepare an alkali antimonide bilayer heterojunction photocathode using alkali metal effusion cells have been presented, which could potentially lead to the application of alkali antimonide in the photovoltaics industry.;To further investigate the properties of our fabricated high-performance alkali antimonide photocathodes, a temperature-dependent QE degradation study on the co-deposited alkali antimonide photocathodes has been performed. The decay mechanism of K-Cs-Sb photocathode at an elevated cathode temperature has been revealed. Besides, the atomic force microscopy (AFM) and kelvin probe force microscopy (KPFM) study on alkali antimonide photocathode prepared by sequential and co-deposition recipe have been carried out to quantify both the physical surface roughness and surface potential variation. Systematic AFM and KPFM analysis of alkali antimonide photocathodes have been performed for the first time.