The dielectric function of Mg<sub>y</sub> NiH<sub>x</sub> thin films (2 ≤ y ≤ 10)

Journal article (2007)

Authors

W. Lohstroh Vrije Universiteit Amsterdam
R. J. Westerwaal Vrije Universiteit Amsterdam
J. L.M. van Mechelen Vrije Universiteit Amsterdam
H. Schreuders Vrije Universiteit Amsterdam
B. Dam Vrije Universiteit Amsterdam
Ronald Griessen Vrije Universiteit Amsterdam
Affiliation
External organisation
Hydrogen storage Thin films Light absorption and reflection
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Published Date

2007

Language

English

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Abstract

Mgy Ni (2 ≤ y ≤ 10) thin films covered with a Pd cap layer are hydrogenated in 1 05 Pa H2 between room temperature and 80 ° C and their dielectric function over(ε, ̃) is determined from reflection and transmission measurements. The hydrogenated Mgy NiHx thin films show a continuous shift of the optical absorption towards higher photon energies with increasing y. Comparison of the obtained dielectric functions with predictions from an effective medium theory show that a considerable doping of the Mg2 NiH4 host takes place at least for y ≤ 3.5 while no signature of MgH2 is observed in that composition range in the optical spectra. This is in contrast to the predictions from the bulk phase diagram where a mixture of semiconducting Mg2 NiH4 (energy gap Eg = 1.6 eV) and MgH2 (Eg = 5.6 eV) is expected.