Carbon Coatings with Low Secondary Electron Yield

Carbon thin films for electron cloud mitigation and anti-multipacting applications have been prepared by dc magnetron sputtering in both neon and argon discharge gases and by plasma enhanced chemical vapour deposition (PECVD) using acetylene. The thin films have been characterized using Secondary Electron Yield (SEY) measurements, Scanning Electron Microscopy (SEM), Nuclear Reaction Analysis (NRA) and X-ray Photoelectron Spectroscopy (XPS). For more than 100 carbon thin films prepared by sputtering the average maximum SEY is 0.98+/-0.07 after air transfer. The density of the films is lower than the density of Highly Ordered Pyrolytic Graphite (HOPG), a fact which partially explains their lower SEY. XPS shows that magnetron sputtered samples exhibit mainly sp2 type bonds. The intensity on the high binding energy side of C1s is found to be related to the value of the SEY. Instead the initial surface concentration of oxygen has no influence on the resulting SEY, when it is below 16%. The thin films produced by PECVD have a much higher maximum SEY of 1.49+/-0.07. Storage conditions in air, namely wrapping in aluminium foil, preserves the low SEY by more than one year. Such coatings have already been applied successfully in accelerators and multipacting test benches.