Substrate effects on indentation plastic zone development in thin soft films

Abstract

Plastic zone evolution in Al-2 wt% Si metal films on silicon and sapphire substrates was studied using nanoindentation and atomic force microscopy (AFM). AFM was used to measure the extent of plastic pileup, which is a measure of the plastic zone radius in the film. It was found that the plastic zone size develops in a self-similar fashion with increasing indenter penetration when normalized by the contact radius, regardless of film hardness or underlying substrate properties. This behavior was used to develop a hardness model that uses the extent of the plastic zone radius to calculate a core region within the indenter contact that is subject to an elevated contact pressure. AFM measurements also indicated that as film thickness decreases, constraint imposed by the indenter and substrate traps the film thereby reducing the pileup volume.

Mechanical Properties of Evaporated Gold Films. Hard Substrate Effect Correction

“…One of the main problems of this model is that the Berkovich tip is a three-sided pyramid, and that the film elastic modulus is assumed to be known. Thin film Young's modulus may range with grain size and film thickness [11], thus it is difficult to know the modulus prior to film testing. An improved method using a conical tip has been suggested [5], and the reduced modulus can be written as:…”

Probing Macromolecular Dynamics and the Influence of Finite Size Effects

“…The formation of piled-up rims has been attributed to the strain, strain capacity, strain rate, and strain hardening susceptibility of the material. In confined systems, a rigid boundary interacting with the stress field during indentation (bit writing) may alter the stress and strain distributions, leading to bulk-deviating mechanical responses [119][120][121][122]. For indentations in compliant films, increased rim heights are observed when elastic strain and plastic flow are constrained, or shielded, by a rigid substrate [119][120][121][122].…”

“…In confined systems, a rigid boundary interacting with the stress field during indentation (bit writing) may alter the stress and strain distributions, leading to bulk-deviating mechanical responses [119][120][121][122]. For indentations in compliant films, increased rim heights are observed when elastic strain and plastic flow are constrained, or shielded, by a rigid substrate [119][120][121][122]. In the case of rigid films on compliant substrates, the plastic yield of the underlying substrate accommodates an enhanced sink-in of the surface around indentation sites [120].…”

“…The rim enhancements were effectively masked by adding a compliant 230 nm thick crosslinked buffer film (PS-BCB) between the rigid substrate and the indented PS film. Substrate effects during quasi-static indentations, such as enhanced rim heights because of strain shielding, are well known for indentation depths exceeding 10 to 30 % of the film thickness [119][120][121][122]. However, the substrate effects in Fig.…”

Hardness of Thin Films and the Influential Factors

“…This is quite logical for the thin films, since their thickness is lower than 1000 nm; the depth of the hole should be around 100 nm. These units can be easily measured with the current technology [9]. In this topic, the impact of the hole's geometric shape on the mechanical properties, that is, hardness, also attracted the attention of the researchers [3].…”