Preparation of Polycrystalline and Thin Film Metal Photocathodes for Normal Conducting RF Guns

Sonal Mistry, Michael Cropper, Adrian Hannah, Keith Middleman, Boris Militsyn, Tim Noakes, Reza Valizadeh, Schaa, Volker R.W. (Ed.), Henderson, Stuart (Ed.), Akers, Evelyn (Ed.), Satogata, Todd (Ed.)
A comparison of quantum efficiency (QE) and work function (wf) measurements of polycrystalline and thin film metal photocathodes for use in NCRF guns, similar to the S-band gun under development for CLARA project at Daresbury, are reported. Cu and Nb thin films were grown onto a Si substrate by magnetron sputtering and subsequently were prepared by annealing and Ar ion sputtering. To determine the surface chemistry, x-ray photoelectron spectroscopy was employed. QE measurements were enabled
more » ... ts were enabled using a UV laser source giving 266 nm light. Wf measurements were carried out using a kelvin probe and ultraviolet photoelectron spectroscopy. Annealing the Cu thin film to 250°C yielded a QE of 1.2E-4; one order of magnitude higher than the QE for sputter cleaned and post annealed polycrystalline Cu. The optimum QE measurement for Nb thin film was 2.6·10⁻⁴, which was found to be comparable to the results obtained for cleaned bulk Nb. Analysis of XPS data of these metals suggest surface composition and surface chemistry are main contributing factors to the QE and WF.
doi:10.18429/jacow-ipac2015-tupje058 fatcat:o3yn25gchfdizbkvqrpj3qdg2y