Understanding the Time‐Dependent Mechanical Behavior of Bimodal Nanoporous Si–Mg Films via Nanoindentation

This study addresses the mechanical response of nanoporous Si–Mg films, which are fabricated using free‐corrosion dealloying and which represent an intriguing form of silicon that may find use as an anode material in lithium‐ion batteries. The porous thin‐film samples, in both the as‐dealloyed and annealed states, are designed to have a final thickness of ≈1 µm so that substrate effects can be avoided during mechanical characterization in both the time and frequency domains. The as‐dealloyed and annealed samples are investigated using a modified continuous stiffness measurement (CSM) technique that optimizes the ability to achieve steady‐state harmonic motion, such that accurate phase angle measurements can be obtained; the as‐dealloyed and annealed samples exhibit distinct phase angles of 1.9° and 2.6°, respectively. Observations made in the time domain suggest that the time dependence of nanoporous Si–Mg stems largely from plasticity. The reduced modulus values of as‐dealloyed and annealed samples are investigated using the CSM technique and have corresponding values of 5.78 and 11.9 GPa, respectively. Similarly, the hardness of as‐dealloyed and annealed samples are 167 and 250 MPa, respectively.