Towards dark current suppression in metallic photocathodes by selected-area oxidation

Abstract

Oxide-free surfaces of polycrystalline Cu are prepared using acetic acid etching after chemical-mechanical polishing. UV ozone treatment is shown to increase the work function of the cleaned Cu by up to 0.5 eV. There is also a large reduction in quantum efficiency at 265 nm. Cu sheet can be easily masked from ozone exposure by Si or glass, meaning that selected-area oxi-dation is possible. Oxygen plasma treatment has a similar effect to the UV ozone but is more difficult to mask. There is no increase in surface roughness after oxidation, meaning that the larger work function could significantly re-duce dark current in accelerator photocathodes without affecting the desired photoemission region.

Highlights

• •

  UV ozone treatment increases the work function of clean Cu by up to 0.5 eV.

• •

  A simple mask of silica glass or Si protects the Cu from ozone exposure.

• •

  Prospects for dark current reduction in accelerators are discussed.

• •

  An efficient polish-etch method for surface oxide-free Cu is given.