Initial Growth Process of Cu Thin Films on bcc-FeCo/MgO(100) via Molecular Beam Epitaxy

We investigated the thickness-dependent structural evolution of Cu/FeCo(100) thin films grown by molecular beam epitaxy (MBE). At the initial stage of growth, Cu adopted a body-centered cubic (bcc) structure templated by the underlying FeCo substrate. Once the Cu thickness exceeded approximately 3 nm, a structural transformation into the face-centered cubic (fcc) phase was observed. The MBE-grown films exhibited interfacial dislocations and developed a disordered surface in the thickness range of 3–5 nm. Although metastable ultrathin bcc-Cu films on FeCo(100) grown by MBE are less stable than sputtered multilayers, MBE offers a unique advantage: it enables in-situ advanced characterization such as angle-resolved photoemission spectroscopy (ARPES) in the ultrathin regime around 1 nm. This capability is essential for designing high-performance devices and probing interface-driven electronic phenomena.