The dielectric function of Mgy NiHx thin films (2 ≤ y ≤ 10)
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)
R. Griessen (Vrije Universiteit Amsterdam)
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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.
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