The role of Mg 2Si formation in the hydrogenation of Mg film and Mg nanoblade array on Si substrates

Abstract

In this paper, both an Mg film and an Mg nanoblade array have been first fabricated directly on Si substrates and hydrogenated under 20 bar hydrogen pressure at temperatures ranging from 200 °C to 350 °C. It is found that Mg 2Si alloy starts to form at T = 200 °C in both the Mg samples, which produces a two-layered structure in the hydrogenated films with the bottom dense layer of Mg 2Si. To prevent Mg alloying with Si, a layer of 200 nm thick Ti film was deposited in between the Mg samples and Si substrates as a diffusion barrier, and their hydrogenation results show that Mg 2Si formation is suppressed greatly and even eliminated in nanoblades, though Mg 2Si hillock defects are observed in the hydrogenated films, which could be formed progressively through the pinholes in the Ti film. To improve the diffusion barrier, a unique structure, consisting of layers of Ti nanorod array and Ti film, has been designed for Mg-based nanostructure deposition. The hydrogen cycling study demonstrates that the structure of 450 nm Ti nanorods on 1 μm Ti film can endure enough number of cycles for the hydrogen storage kinetic and thermodynamic study of film-based Mg nanostructures with/without nanocatalyst, and thus one can gain a fundamental understanding of hydrogen interacting with Mg intrinsic nanostructures and nanocatalysts.