The effects of Si and expanded PTFE substrates on formation and hydrogenation of Mg and Mg–Ti films

• We have investigated the hydrogenation dependence on film–substrate interface.
• Mg and Mg–Ti films were deposited on Si and expanded PTFE substrates.
• Two different plasma modes were used to modify of surface of Si and ePTFE.
• Surface properties of Si and expanded PTFE substrates are thoroughly analysed.
• Disparities between hydrogenation of films on different substrates were identified.

In this work, we investigated how DC and pulsed DC Ar gas plasma treatment changes surface topography and chemical composition of silicon and expanded Polytetrafluoroethylene (ePTFE) substrates and how different surface pretreatment techniques can affect the formation and hydrogenation of Mg and Mg–Ti films. It is observed that pre-treating Si and ePTFE substrates with different plasma modes results in significant changes of microstructures of as-deposited Mg and Mg–Ti films. After the hydrogenation of Mg films at 20 bar H2 pressure and 180 °C temperature the formation of crystalline MgH2 phase is observed only for the films deposited on plasma non-treated Si substrates which had the films with smallest dimensions of its columnar structure. It is known that, usually, Ti additives has positive effect on hydrogenation properties of Mg, but in this study independently of the used substrate pre-treatment technique after the hydrogenation of Mg–Ti films their XRD analysis showed no peaks of the crystalline hydride phase. However, depending on the surface properties of the substrate after hydrogenation Mg–Ti films also have several disparities which are discussed and attributed to the potentially related substrate features.