Tetragonal structure of thin nickel films on Cu(001)

The crystallographic structure of thin Ni films deposited on Cu(001) has be en studied using Surface Extended X-ray Absorption Fine Structure (SEXAFS). Taking advantage of the linear polarization of the synchrotron radiation, we have shown that Ni adopts the Cu lattice parameter parallel to the inter face. This lateral expansion induces a longitudinal compression of the unit cell, leading to a face centered tetragonal structure of the Ni films from 3 to 10 monolayers. The temperature dependence of the EXAFS oscillations h as allowed to measure strain inside the Ni layers.