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NEA surface activation of GaAs photocathode with different gases

•The NEA activation of GaAs cathode with O2, CO2, CO and N2 was examined.•The QE was 2.3% with CO2 which was lower than that with O2.•CO and N2 did not activate the NEA GaAs cathode at all.•The low quantum efficiency of the activation of CO2 can be explained with the degradation by CO to the NEA sur...

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Bibliographic Details
Published in:Surface science 2017-10, Vol.664, p.65-69
Main Authors: Guo, L., Kuriki, M., Iijima, H., Uchida, K.
Format: Article
Language:English
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Summary:•The NEA activation of GaAs cathode with O2, CO2, CO and N2 was examined.•The QE was 2.3% with CO2 which was lower than that with O2.•CO and N2 did not activate the NEA GaAs cathode at all.•The low quantum efficiency of the activation of CO2 can be explained with the degradation by CO to the NEA surface. The GaAs photo-cathode is a unique device which is able to generate highly polarized electron beam up to 90% and an extremely small emittance beam. The photo-electron emission is possible with IR (Infrared Red) and visible light and the quantum efficiency can be more than 20%. These unique features depend on the negative electron affinity (NEA) surface made by adsorption of Cs and O2/NF3, but this surface is easily damaged by residual gas adsorption, ion back-bombardment, etc. The exact structure of the NEA surface is not known, even there are several hypotheses. In this study, we performed the NEA activation on a cleaned GaAs surface with CO2, CO, N2, and O2 gases and compared the results to improve our understanding on the NEA surface. We found that the NEA activation with CO2 is similar to that with O2, but the maximum QE value is significantly lower than that with O2. We also found that N2 and CO gases did not contribute to NEA activation at all. By analyzing CO2 activation, we found that atomic oxygen activates the NEA surface and CO degrades the NEA surface simultaneously. We found that the NEA activation ability of atomic oxygen is almost a half of that of O2 molecule.
ISSN:0039-6028
1879-2758
DOI:10.1016/j.susc.2017.06.001