Graphene is considered a suitable atomically thick layer on photocathodes, and the photoemission performance of the graphene-covered photocathodes can be enhanced through Cs/O activation. To investigate the effects of the substrate materials beneath the graphene layer on Cs/O deposition and photoemission performance. We compare the activation processes and photoemission performances of few-layer graphene supported by nickel and copper to investigate the effects of the substrate materials beneath the graphene layer on Cs/O deposition and photoemission performance. By Cs/O activation, the nickel-supported few-layer graphene can possess a higher response at 405 nm, while the copper-supported cathode can acquire a wider spectral response and better stability. After degradation, we discover that the samples supported by nickel and copper can act differently through the additional Cs/O deposition processes, while the surface barrier heights of both samples are further decreased.
Electron source can be considerably benefited from the application of photocathodes with long lifetime, broad spectral response and high quantum efficiency. As graphene has exhibited potential to serve as the passivation layer to improve electron emission behavior of photocathodes due to its unique structure and properties, exploring photoemission phenomenon of metal-supported graphene material can help to develop robust photocathodes. We report the photoemission performance of the nickel-supported monolayer graphene through various activation processes. To investigate the effects of different activation processes on this composite material, we compare the photoemission behavior of the nickel-supported monolayer graphene by cesium (Cs)-only activation at room temperature, Cs-only activation under heated condition and cesium-oxygen (Cs/O) activation under heated condition. The experimental results show that these activation methods are able to promote photoemission ability of the nickel-supported monolayer graphene. Among them, the Cs/O activation process under heated condition can improve the photocurrent most significantly. This process validation of activating the nickel-supported graphene material provides a new route to enhance photoemission performance of metal photocathodes, and the activation method could be applied to the surface modification of other metal-supported graphene materials.
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