Atomistic simulations of the vapor deposition of Ni/Cu/Ni multilayers: The effects of adatom incident energy

Vapor deposited multilayers consisting of a low electrical resistivity conductor sandwiched between ferromagnetic metals such as cobalt or nickel-iron alloys sometimes exhibit giant magnetoresistance (GMR). The GMR properties of these films are a sensitive function of structure and defects in the films and therefore depend upon the processing conditions used for their synthesis. A three-dimensional molecular dynamics method has been developed to simulate the [111] growth of model Ni/Cu/Ni multilayers and was used to investigate the role of vapor atom impact energy upon the film structure and defects. High incident atom energies were found to lower interfacial roughness but promoted intermixing by an atomic exchange mechanism. Low incident energies reduced intermixing, but resulted in films with rough, defective interfaces. The simulations identified an intermediate incident energy between 1 and 2 eV that resulted in both low roughness and intermixing, and an anticipated large GMR effect. The simulation methodology was extended to explore the benefits of a modulated incident atom energy deposition strategy. When a thermal energy was used to deposit the first few monolayers of each new metal layer, intermixing by the exchange mechanism during subsequent hyperthermal energy deposition could be eliminated, and films with almost no interfacial roughness or intermixing could be grown. The modulated energy deposition method can be simply implemented using ion beam deposition.