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Thin films of TiN having low secondary electron emission (SEE) yields are coated on alumina rf windows in order to suppress the occurrence of multipactor. It is necessary to form films with a proper thickness in order to obtain a sufficient reduction of SEE as well as to avoid any excessive ohmic loss in conductive TiN films. For an optimization of the film thickness on an alumina surface, measurements of the SEE coefficients, and ohmic losses in the rf (S-band) field were carried out. High-power examinations of the coated windows were also performed. The results show that TiN films with a thickness of 0.5 nm or greater on alumina ceramics have SEE coefficients of less than unity at an incident energy of 10 keY. High-power tests have revealed that the "going away" of TiN films is probably due to excessive ohmic losses taking place when the thickness is greater than 1.5 nm. It is concluded that optimized film thickness for window coatings is 0.5-1.5 nm.

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