posted on 2021-07-20, 15:39authored byGiorgio Cortelli, Luca Patruno, Tobias Cramer, Mauro Murgia, Beatrice Fraboni, Stefano de Miranda
The nanomechanical
properties of ultrathin and nanostructured films
of rigid electronic materials on soft substrates are of crucial relevance
to realize materials and devices for stretchable electronics. Of particular
interest are bending deformations in buckled nanometer-thick films
or patterned networks of rigid materials as they can be exploited
to compensate for the missing tensile elasticity. Here, we perform
atomic force microscopy indentation experiments and electrical measurements
to characterize the nanomechanics of ultrathin gold films on a polydimethylsiloxane
(PDMS) elastomer. The measured force-indentation data can be analyzed
in terms of a simple analytical model describing a bending plate on
a semi-infinite soft substrate. The resulting method enables us to
quantify the local Young’s modulus of elasticity of the nanometer-thick
film. Systematic variation of the gold layer thickness reveals the
presence of a diffuse interface between the metal film and the elastomer
substrate that does not contribute to the bending stiffness. The effect
is associated with gold clusters that penetrate the silicone and are
not directly connected to the ultrathin film. Only above a critical
layer thickness, percolation of the metallic thin film happens, causing
a linear increase in bending stiffness and electrical conductivity.