Influence of compressive biaxial strain on the hydrogen uptakeof ultrathin single-crystal vanadium layers

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Abstract
We have investigated the influence of biaxial compressive strain on the thermodynamic properties of hydrogen in thin, single-crystal vanadium layers (0.9, 1.6, and 2.0 nm). At H/V0.1, the interaction was found to be extremely weak in the 0.9-nm-thick layer and repulsive in the 1.6- and 2.0-nm-thick V layers. The repulsive interaction was found to increase with increasing layer thicknesses. These results are unexpected as the interaction is attractive in both bulk V and in thin vanadium layers under biaxial tensile strain for H/V<0.5. Both the strained and unstrained vanadium lattices are found to have roughly the same hydrogen affinity at H/V=0.1 (0.3 eV/H). No ordered bulklike Β phase was observed at any concentration (0<H/V⩽1) in the temperature range 30–250t°C. Methods used in this study are resistivity measurements, x-ray diffraction, and nuclear reaction analysis.