Effect of properties of MWPECVD polycrystalline diamond films on photoemissive response

Diamond is an extremely interesting material for photoemission applications, due to the negative electron affinity of its surface, which can be obtained after suitable treatments. In the present work two sets of polycrystalline diamond films, characterized by different thicknesses and deposition conditions, are analyzed. In particular, in the examined films the relationship among the grain size, the amount of non-diamond carbon (sp2) located at the grain boundaries and their efficiency as photocathodes has been found and carefully investigated. The photoemission yield in the UV range is evaluated for all the samples, before and after hydrogenation, and after air exposure. The crucial parameter for the photocathode performances has been found not to be the film thickness, but the properties of polycrystalline diamond films, tunable with the plasma modulation and the methane percentage in the gas mixture.

► We explore two sets of PCD films, with different thicknesses and deposition conditions.
► The photocathode performance is tunable with plasma modulation and CH4 percentage.
► In untreated samples quantum efficiency, QE, is linked to the highest sp2 component.
► In the hydrogenated ones QE enhances in the thickest films with the largest grains.
► The hydrogenation treatment is more effective on the diamond phase of the film.