Evaluation of critical depth ratio for soft V2O5 film on hard Si substrate by finite element modeling of experimentally measured nanoindentation response

Abstract

A combined nanoindentation experiment and finite element modeling (FEM) approach was utilized in the present work to evaluate the effects of variations in the ratio (h/t) of indentation depth (h) to film thickness (t) on the nanomechanical behavior of 2.3–6.2 μm vanadium pentoxide (V2O5) films. The soft V2O5 films were deposited by pulsed radio frequency magnetron sputtering on a relatively hard silicon (Si) substrate. The elasto-plastic properties of the V2O5 films as well as the Si substrate were evaluated using a power law-based nonlinear material model. Based on the present nanoindentation and FEM results the critical penetration depth to film thickness ratio (h /t)c, i.e. critical depth ratio (CDR) was predicted as 7.9%,,confirming thereby that there is no universal critical penetration depth beyond which the mechanical properties of the substrate start to affect the evaluated nanomechanical properties (e.g. nanohardness H, Young’s modulus E, etc) of a given soft film on a given hard substrate. The experimental data showed that at h ~ 0.5t the magnitudes of E and H were approximately two times the values measured at h ⩽ 0.1t. The FEM results obtained in the present work successfully predicted the effects of variations in the h /t ratio on the indenter displacements as well as the distributions of the von Mises stress for the soft V2O5 films on the hard Si substrate system.