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Metal-Semiconductor Transition on the Surface and in the Bulk of Europium Hydride Thin Film

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Knor M., Nowakowski R., Duś R.

Acta Physica Polonica A

2012

vol. 122

issue 4

698-703

Thin europium films (20-50 nm thick) on a glass substrate were transformed into EuH_x (0 < x < 2) by interaction with H_2 introduced into the reactor in successive calibrated doses. By measuring the pressure, the hydrogen uptake (H/Eu) was determined at every step of the reaction. In situ monitoring of bulk properties (electrical resistance R(H/Eu), relative transparency to light T(H/Eu)/T_0 and (H/Eu) dependent light transparency spectrum) confirms metal-semiconductor transition at room temperature. Both the electrical resistance and optical transparency of the film strongly increase with hydrogen concentration as a consequence of the resulting increase of the content of semiconducting dihydride. Moreover, the course of work function changes ΔΦ(H/Eu) indicates inversion of the charge-transfer direction on the surface. The transition at room temperature from positively to negatively polarized hydrogen adsorbate was observed in situ during hydrogen uptake. As a result, the work function at equilibrium state varies with hydrogen content from +18 to -18 mV with respect to pure metal film, reflecting the change of "mirror potential" generated on the surface due to the accumulation of hydrogen adsorbates in the subsurface region.

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1 Acta Physica Polonica A

1 2012

1 Duś R.

1 Knor M.

1 Nowakowski R.

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Metal-Semiconductor Transition on the Surface and in the Bulk of Europium Hydride Thin Film