Atom probe tomography of ion-irradiated ultra-thin Fe/Cr/Fe trilayers with sub-nm spatial resolution

Abstract

Ion-bombardment effects in a magnetic trilayer Fe (10 nm)/Cr (0.7 nm)/Fe (10 nm) system have been studied by 3D atom probe tomography (APT). The films were bombarded by 30 keV Ga+ ions at low fluences. From APT, the positions of individual Cr and Fe atoms could be located with sub-nm spatial resolution, both before and after ion bombardment. In the pristine specimen the presence of the 0.7 nm Cr layer was verified and individual lattice planes with a spacing of ∼0.15 nm were identified which would correspond to the monolayer spacing of the Fe lattice, in agreement with the growth process. Upon irradiation, the Cr layer is broadened to ∼1.2 nm at a fluence of 3 × 1014 Ga+ cm−2 and to ∼3.4 nm at 3 × 1015 Ga+ cm−2. Computer simulations indicate that, at a fluence of 3 × 1014 Ga+ cm−2, each Cr atom in the intermediate layer is displaced on average once in the collision processes.