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

Abstract

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 ͑GMR͒. 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 ͓111͔ 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.

Atomically engineering Cu/Ta interfaces.

“…Previous studies [23,25,32] have indicated that when the underlying surface is composed of atoms with a lower cohesive energy, a larger lattice spacing, and a lower surface energy with respect to the depositing atoms, the depositing atoms are more likely to penetrate the underlying surface through the lattice interstices and the underlying atoms are more likely to be exchanged to the surface to release both surface tension and surface energy. A continuous surface segregation of the underlying atoms to the surface then causes them to be mixed into the overlying deposited layer.…”

“…The adatom energy effect on surface roughness of growth films has been well studied. [23,32] When an adatom with a higher energy impacts a surface with a local asperity, the impact is more likely to cause the collapse of the asperity, resulting in a flattening of the surface.…”

“…To verify this observation, a series of Cu films were experimentally grown on Ta using BTIBD technique at different sputtering energies between 400 eV and 1200 eV. According to previous analyses, [32,33] the applied sputtering energy range roughly corresponds to the simulated adatom energy between 0.1 and 4.0 eV. AFM was used to measure the surface morphology of the deposited films.…”

Directed Vapor Deposition: Low Vacuum Materials Processing Technology

“…University of Virginia,Materials Science and Engineering Department,Charlottesville,VA,22904-4745 8. PERFORMING ORGANIZATION REPORT NUMBER…”

“…The carrier gas flow appears to increase the angular distribution and lower the energy of atomic deposition [3]. Atomistic modeling has shown that both of these characteristics can lead to the generation of highly defected, porous coatings [8].…”