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- Andersson, Gabriella
(author)
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Hydrogen in ultrathin vanadium layers
- 1999
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Doctoral thesis (other academic/artistic)abstract
- The influence of elastic boundary conditions on the thermodynamics of hydrogen in vanadium were investigated using resistometry, x-ray diffraction and nuclear reaction analysis. To provide varying lattice strain states Mo/V (110) and Fe/V (001) superlattices with thickness L of individual layers in the range 3-16 monolayers (ML) were used. In addition the thickness ratio LFe/LV in the latter samples was varied. The results were compared with earlier work on Mo/V (001) superlattices.In the Mo/V (110) superlattices the H-H interaction was found to be repulsive in contrast to the (001) oriented samples and bulk V. This was also the case for Fe/V (001). For the thickness ratios LFe/LV = 3/10 and 3/16 it was found that the hydrogen-depleted interface region in V was populated at lower average concentration than in the symmetric samples (LFeLV = 1). This was related to the decreased Fe thickness.For Fe(3ML)/V(12-15 ML) samples the effects of hydrogenation on the magnetic exchange coupling between the Fe layers were investigated using neutron reflectometry. For 12 and 14 ML of V the coupling was switched continuously from antiferromagnetic (AFM) to ferromagnetic (FM) upon introduction of small amounts of hydrogen, whereas the initially FM-coupled 15-ML sampleexhibited an antiferromagnetic "resonance" at H/V ≈ 0.02. This was found to be due to changes in the vanadium Fermi surface. An intermediate state of noncollinear coupling was also observed in the 14-ML sample.
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| 2. |
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| 3. |
- Andersson, Gabriella, et al.
(author)
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Influence of compressive biaxial strain on the hydrogen uptake of ultra-thin, single crystal vanadium layers
- 1997
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In: Physical Review B. - 0163-1829. ; 55:3, s. 1774-1781
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Journal article (peer-reviewed)abstract
- We have investigated the influence of biaxial compressive strain on the thermodynamic propertied of hydrogen in thin, single-crystal vanadium layers (0.9, 1.6, and 2.0 nm). At H/V<0.1 (atomic ratio), the host-mediated H-H interaction was found to be attractive. For H/V>0.1, 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 HV<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 beta phase was observed at any concentration (0
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