Epitaxial growth of body-centered-tetragonal copper

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Abstract
Deposition of Cu in ultrahigh vacuum on a clean Pd{001} surface leads to the growth of a new crystalline Cu phase with body-centered-tetragonal (bct) structure well ordered up to about 10 layers. A low-energy electron-diffraction (LEED) analysis of 6-layer films finds the bulk lattice parameters to be a=2.75 Å and c=3.24 Å, with little relaxation of the surface layers. Photoemission experiments confirm that the grown phase is different from the stable fcc modification and show a surface state 4.8 eV below the Fermi energy which is not present in fcc Cu. The grown phase may correspond to a theoretically predicted bct phase under slight strain, but we also show directly that it is probably strained bct and not strained bcc or fcc.