Metal-Semiconductor Transition on the Surface and in the Bulk of Europium Hydride Thin Film |
| M. Knor, R. Nowakowski and R. Duś
Institute of Physical Chemistry, Polish Academy of Sciences, M. Kasprzaka 44/52, 01-224 Warszawa, Poland |
| Received: April 17, 2012; in final form August 30, 2012 |
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| Thin europium films (20-50 nm thick) on a glass substrate were transformed into EuHx (0 < x < 2) by interaction with H2 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)/-T0 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. |
| DOI: 10.12693/APhysPolA.122.698 PACS numbers: 67.63.Gh, 73.61.-r, 78.66.-w, 73.20.-r |