Metal-ion-controlled growth and nanoindentation response of 3D, bicontinuous Cu–Fe thin films

Abstract

Bicontinuous, nanocomposite thin film morphologies depend largely on the deposition conditions applied during physical vapor deposition. With the introduction of high-power impulse magnetron sputtering (HiPIMS), the range of potential morphologies achieved during deposition has been increased. In this work, we compare the deposition outcomes between traditional direct-current magnetron sputtering (DCMS) and HiPIMS for a thin film co-deposit of Cu and Fe. Modular control of the columnarity, porosity, and roughness was achieved by varying the Cu and Fe metal ion currents during deposition. The directionality of the nanostructured phase-separated morphology was also controlled as the ion current increased. At zero ion current for both Cu and Fe sputtered species during DCMS, the film exhibited lateral concentration modulations of Cu and Fe. The directionality of the Cu- and Fe-rich phases shifted to vertical concentration modulations at low ion currents of IFe=1A and ICu=0.1A and to lateral concentration modulations at relatively moderate ion currents of IFe=5A and ICu=2A. At high ion currents of IFe=18A and ICu=2A, a more randomized phase domain structure was observed on the nanoscale. This structural shift is rationalized using an interdiffusion model. The role of different kinds of phase-separated morphologies, achieved during DCMS deposition, on the mechanical properties has also been studied. Results indicated an increase in hardness, indentation modulus, and flow strength values with the increase in indentation strain rates. Bicontinuous Cu–Fe nanocomposites are found to be stronger than multilayer Cu–Fe samples.