Effects of air exposure on ion beam assisted TiN:O coatings to prevent multipactor

Titanium nitride films are used to prevent 'multipactor' plasma in rf devices due to their low secondary electron emission coefficient (σ) in ultrahigh vacuum. This work refers to the increase of this coefficient on exposure to air and the effect of ion beam assisted deposition (IBAD) on its recovery, relevant in components for space applications. Two modes of deposition were compared: a simple sublimation of titanium in nitrogen atmosphere and a low energy (200 eV-Ar+) IBAD. The sample characterization included σ, bulk and surface compositions, by energy dispersive analysis of x rays and x-ray photoelectron spectroscopy, structure, and resistivity. When the coatings were clean they presented a low value of σ, which increases after exposure to air and recovers part of its low value by electron irradiation in ultrahigh vacuum. In IBAD samples recovery in σ, surface nitrogen content and stability were higher than in simple sublimation ones, leading to values of σ closer to one. After weeks in air, the aluminum microwave guide elements coated with IBAD TiN:O showed a 'multipactor' threshold power three times higher than those coated with non-IBAD TiN:O. The coatings' resistivities lay in the 1-7 μΩ m range