Growth and study of epitaxial V thin films

Sammanfattning

Single crystal films, fabricated through epitaxial growth processes, can serve as model systems from which fundamental material properties may be studied. In the particular case of epitaxially grown vanadium, structural properties related to finite size effects and resulting changes to hydrogen related properties are important to understand for any study of more complex systems. The aim of this project was to grow high quality epitaxial vanadium on MgO (001) substrates using magnetron sputtering and study the crystal structure for varying film thickness through XRR and XRD. AFM and RHEED were used to study growth and substrate quality, and NRA was used to determine the hydrogen concentration in loaded films. Growth conditions were found for which high quality vanadium crystals could be grown with film thickness varying between 50 and 500 Å. Measurements of the 002 vanadium diffraction peak for films of varying thickness showed an increased strain for thinner films with a large and irregular out-of-plane expansion of the lattice parameter for films at or below 100 Å, in some instances around or exceeding 4%. The results demonstrate the influence of variations in the MgO quality on the crystals that are grown. The considerable expansion of the crystals for thin films indicates structural changes, possibly due to the finite size and interface effects, that are not fully understood and should be investigated further.