• Schreuders, Herman
• Züttel, A.
• Griessen, R.
• Chacon, C.
• Hjörvarsson, B.
• Mechelen, J. L. M. Van
• Dam, Bernard
• Borgschulte, A.
• Gremaud, R.

Abstract

<p>The structural, optical and dc electrical properties of Mg _xAl_1-x (0.2 ≤ x ≤ 0.9) gradient thin films covered with Pd/Mg are investigated before and after exposure to hydrogen. We use hydrogenography, a novel high-throughput optical technique, to map simultaneously all the hydride forming compositions and the kinetics thereof in the gradient thin film. Metallic Mg in the Mg_xAl_1-x layer undergoes a metal-to-semiconductor transition and MgH₂ is formed for all Mg fractions x investigated. The presence of an amorphous Mg-Al phase in the thin film phase diagram enhances strongly the kinetics of hydrogenation. In the Al-rich part of the film, a complex H-induced segregation of MgH₂ and Al occurs. This uncommon large-scale segregation is evidenced by metal and hydrogen profiling using Rutherford backscattering spectrometry and resonant nuclear analysis based on the reaction ¹H(¹⁵N, αγ)¹²C. Besides MgH₂, an additional semiconducting phase is found by electrical conductivity measurements around an atomic [Al]/[Mg] ratio of 2 (x = 0.33). This suggests that the film is partially transformed into Mg(AlH₄)₂ at around this composition.</p>

Topics

• impedance spectroscopy
• amorphous
• phase
• thin film
• semiconductor
• Hydrogen
• forming
• phase diagram
• electrical conductivity
• spectrometry
• Rutherford backscattering spectrometry