The Impact Of H-2 And N-2 On The Material Properties And Secondary Electron Yield Of Sputtered Amorphous Carbon Films For Anti-Multipacting Applications

Amorphous carbon thin films were prepared by direct current hollow cathode sputter deposition in Ar discharge with the injection of small amounts of H-2 and/or N-2. The influence of these additives on the film properties with particular focus on the application as a coating for electron cloud mitigation in particle accelerators is characterized by optical spectroscopy, X-ray photoelectron spectroscopy, and secondary electron yield (SEY) measurements. The SEY maximum increased from initially 0.98 with pure Ar in the gas discharge up to 1.38 at 0.5% H-2 while the addition of 1% of pure N-2 enabled to reduce it to 0.88. The simultaneous addition of N-2 to the H-2 containing discharge allowed an average SEY maximum reduction of 20%. The optical bandgap revealed a correlation between the increase/decrease of the bandgap and the SEY increment/reduction for H-2/N-2 addition. The surface composition changes and the resulting modification of the sp(2)/sp(3) ratio correlate with the changes in SEY and optical properties. The obtained results highlight the potential of intentionally injected N-2 to counteract the detrimental effect of the inevitable H-2 partial pressure in the coating systems during the production of amorphous carbon thin films for anti-multipacting applications in particle accelerators.