Metastable body-centered-tetragonal phase of vanadium on Cu{001}

Pseudomorphic ultrathin films of vanadium on Cu{001} up to about 14 {} thick have a body-centered-tetragonal structure with a=2.556 and c=4.40±0.10, as determined by quantitative low-energy electron-diffraction analysis. Despite the low accuracy of the quantitative results, which is due to the high densities of defects and disorder in the grown films, use of the epitaxial Bain path leads to unambiguous identification of the films' structure as a strained state of the metastable equilibrium bct phase of vanadium at $c/a=1.78,$ rather than a strained state of the bcc ground state at $c/a=1.$