Surface modification of few-layer graphene on metal and semiconductor substrates by Cs/O activation

Exploring photocathodes with advantages of visible-light response, high quantum efficiency and long lifespan has been the hot issue in electron sources. The implementation of a 2D material protective layer is considered a promising approach to extending the operating lifetime of photocathodes. To investigate the differences in surface modification among the different materials beneath the graphene layer. The few-layer graphene was transferred onto the Cu and Ni metal substrates and p-type GaAs and Si semiconductor substrates. After the Cs/O alternating activation, the photoemission behaviors, including photocurrent evolution, spectral response and degradation characteristic were investigated. The in-situ XPS/UPS spectra were characterized to present the changes of the surface chemical states and the work function after Cs/O activation and degradation. This work can provide a technical approach for developing graphene-protected photocathodes.