Analysis of structural stability of Ar ion-implanted Pd/Zr/Pd/Ti/Pd multilayer stack in hydrogen annealing environment

The influence of 150 keV argon ions at fluences in the range of 1 × 10¹²-1 × 10¹⁶ ions/cm² on the stability of the multilayer stack Pd/Zr/Pd/Ti/Pd thin films system, deposited on Ti and Ti₆Al₄V substrates, under thermal annealing in an H₂ environment was investigated. For samples deposited on Ti substrate, RBS revealed structural instability that increases with fluence. This is evidenced by a decrease in the intensity of layers accompanied by increased consumption of the Pd layers. This effect led to the initial individual layers becoming one compound layer and the formation of a new Ti-O-Pd layer, indicating a complete intermixing of layers at 1 × 10¹⁶ ions/cm². However, for the samples deposited on Ti₆Al₄V substrate, the Pd layers could still be identified and resolved, indicating an incomplete intermixing of layers. XRD revealed the structural transformation of layers via an intermixing process resulting in the formation of two new phases, TiH₂ and ZrH₂, classified as face-centered tetragonal (FCT) crystal structures. ERDA confirmed the presence of hydrides in the system indicating the absorption of H into the system to a maximum H amount of ∼5.2 at.%, at higher fluence, for the same multilayer stack deposited on both substrates.