Abstract
Nanocrystalline Mg films with thicknesses between 45 and 900 nm were prepared by e-beam on fused-SiO
2
substrates and hydrogenated at 280 °C to investigate the H-absorption/desorption process. Films were characterized by XRD, RBS, Raman, FEG, “in situ” optical measurements and TPD-MS. Whereas practically full conversion into MgH
2
is observed in thinner films (
d
< 150–200 nm), higher amount of hydrogen is not absorbed by thicker films (
d
> 200–250 nm) that is attributed to the formation of Mg
2
Si–MgO phases (observed by RBS and Raman) as well as the slow kinetics of MgH
2
formation. H-desorption process is controlled by a nucleation and growth process and hydrogen is released at lower desorption temperatures (
T
d
= 425 °C) than bulk MgH
2
.
T
d are slightly lower (Δ
T
∼ 25 °C) in thickest hydrogenated films (
d
> 200–250 nm) suggesting an influence of Mg
2
Si and MgO phases, formed during hydrogenation.
Highlights
• H-absorption is uncompleted in Mg film with thickness >200 nm.
• Raman and RBS measurements show the formation of Mg
2
Si and MgO due to substrate reaction.
• Mg
2
Si/MgO phase formation will preclude the complete hydrogenation of films.
• No influence of thickness on H-desorption mechanism is observed.
Page:
9865-9865
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