Discrete and continuous deformation during nanoindentation of thin films

Nanoindentation of patterned metal lines on a Si substrate

“…The initial deviation from the elastic response, which occurs over a load range of 45-65 lN, is approximately independent of line width w. The indentation compliance, which can be represented by the curvature of loading response, is also unaffected by line width prior to the initial deviation. The corresponding maximum shear stresses underneath the indenter tip are 1.8-2.0 GPa at the point of deviation, which compares well with the theoretical shear strength of Al ($2.5 GPa), similar to the trends documented for continuous films of Al and Cu [4,6]. Each of these P -h curves exhibits discrete changes (jumps) in the load versus displacement response after the initial deviation from the elastic response as observed in continuous thin films.…”

“…Unlike the elastic response, the P -h response subsequent to this initial deviation is a function of line width w. The curvature of the loading response decreases with decreasing w, indicating a greater indentation compliance for smaller line width. 1 The discrete discontinuities in the P -h response are not as clear as those observed in the indentation of single crystalline continuous films [4,6]. This contrast may arise from the polycrystalline nature of the present material system, as the combination of grain boundaries and grain orientations can alter the motion of dislocations (or plastic flow) during deformation.…”

“…5 show that the response of these cases are essentially indistinguishable up to a load of 400 lN. The initial stage of nanoindentation is often explained by the Ôpunch-outÕ of dislocation loops around the indenter tip [4,5]. When the indenter depth increases, the dislocation density increases by the nucleation of new dislocations and/or the expansion of existing dislocations.…”

“…Nanoindentation has been utilized extensively to probe mechanical properties of thin films [2][3][4]. As this technique can generate large strain (or stress) within the relatively small volume of materials, nanoindentation can be extended to other small-volume structures as well, such as patterned lines and islands on substrates.…”

Discrete dislocation plasticity analysis of the wedge indentation of films

“…Ma and Clarke (1995), Poole et al (1996), Swadener et al (2002), which cannot be accounted for by conventional plasticity. A clear understanding of the indentation size effect and its connection with material strength is especially important in modern applications involving thin films and multi-layers since nano-and micro-indentation are frequently the only means of measuring strength, see, for example, Gouldstone et al (2000) and Lou et al (2003). Readers are referred to Freund and Suresh (2004) for further details and references.…”