Photoemission from metals covered with a nanostructured carbon film

Though present photoemitting cathodes have attained quantum yields, lifetim es, dark currents, and response times as required by high-luminosity accele rators, their use is hampered by their high reactivity to residual gases ev en in ultra-high-vacuum conditions. Ultrathin (20-200 nm) films of nanostru ctured sp(2) carbon, directly grown on photocathodes by supersonic cluster- beam deposition, besides providing a strongly bound, inert protective coati ng, are shown to maintain the photoemission efficiency of clean metallic su bstrate cathodes. Moreover, nanostructured carbon coating is shown to induc e strong nonlinearities in photoemission at high intensities, which can be explained as due to the Auger effect. (C) 2000 American Institute of Physic s. [S0021-8979(00)04208-0].