Development of Multi-Alkali Antimonide Photocathodes for High-Brightness RF Photoinjectors

Multi-alkali antimonide photocathodes can have high quantum efficiency similar to UV-sensitive Cs2Te photocathodes, but with the advantages of photoemission sensitivity inthe green wavelength and a significant reduction in the mean transverse energy of thephotoelectrons. To explore their feasibility for use in a high-gradient RF gun, DESYcollaborated with INFN LASA to develop multi-alkali photocathode materials. Thisdissertation provides detailed insights into the fabrication recipes of various alkali antimonide photocathodes, including K-Cs-Sb, Na-K-Sb, and Na-K-Sb-Cs photocathodes,all of which were grown on a Mo substrate. This thesis also provides information regarding film thickness, substrate temperature, deposition rate, and their possible effects onthe photocathode’s properties. In addition, the influence of temperature on the cathodedegradation is also summarized. Moreover, this report presents a summary of the testresults obtained from the K-Cs-Sb cathodes inside the high-gradient RF gun at PITZ.Furthermore, within the framework of density functional theory (DFT), the dissertation explores the electronic and optical properties of materials like K3Sb, K2CsSb, andNa2KSb. The optical properties, including the dielectric function, reflectivity, refractiveindex, and extinction coefficient, were evaluated. The correlation between the simulatedand measured optical properties, such as reflectivity, provides a more efficient strategyfor rationalizing and understanding the properties of photoemissive materials. This further helps to improve the cathode recipe. This dissertation also outlines such correlationsbetween experimental and simulation results for the aforementioned photoemissive films.This study represents a step forward in the development of multi-alkali photocathodesfor high-charge RF photoinjector applications, providing a valuable characterization ofK-Cs-Sb photocathode performance.