University Siegen, Siegen, Germany
Prospective light sources requires photocathodes with high quantum efficiency (QE), long lifetime and minimized thermal emittance. One promising candidate meeting the aforementioned specifications is GaN. Due to its wide band gap (Eg = 3,4 eV), GaN can be excited by UV-light sources. Its thermal and chemical stability are added bonuses. In the framework of the present activity, the synthesis of GaN films on Si, Cu, Mo and Nb by means of rf magnetron sputtering is proposed. In this context, Ga, GaAs and GaN are suitable source material candidates, which are sputtered in a nitrogen/argon plasma discharge. The conductivity as well as the band-gap of the corresponding films can be modified by dopants like Mg and In, respectively. Standard materials science characterization techniques such as SEM, EDX, XRD or XPS are used to explore the growth mechanism of GaN alongside with a morphological and chemical examination. To assess and optimize the performance of the photocathode the abovementioned requirements are tested in an in-situ setup. In addition to the project outline, first experimental results of GaN coatings synthesized based on a GaAs source sputtered in pure N2 are presented.
University Siegen, Siegen, Germany
During the past three years, we developed a coating along with a corresponding in-situ characterization process in order to realize SRF-gun surfaces featuring low secondary electron yield (SEY). Important aspects that have been accounted for are the homogeneity and adhesion of the coatings deposited on the cylindrical SRF-gun mantle. Furthermore, the correlation between SEY and crystallinity, morphology, and contamination was studied in detail. The SEY maximum can be tuned between 1.5 and less than 0.7 depending on the deposition conditions. In this work, we recap the results and present a general strategy for the effective mitigation of electron cloud multiplication.
