Growth mode of ultrathin Co films on Fe(001) prepared by low energy ion-assisted deposition

Co films were epitaxially grown on Fe(001) by simultaneous thermal evaporat ion of Co atoms and ion bombardment with low-energy (300-1000 eV) Ar ions i n a wide range of ion-to-atom flux ratio (0.02-0.5). The 0-50 ML coverage r ange was investigated, Transition from island growth to a continuous layer growth occurs on passing from purely thermal to ion-assisted deposition pro cedure. Structural characterization was performed by Primary-beam Diffracti on Modulated Electron Emission (PDMEE). For purely thermal deposition, tran sition from the bcc phase to the equilibrium, hcp phase has been observed a t a critical coverage of about 15 ML, both structures showing a significant strain (7% contraction and 5% expansion with respect to the ideal bcc and hcp phase, respectively). Ion assistance has proved to be effective in lowe ring both the strains in the Co film and the critical thickness of the bcc phase.