Dr. Tobias Cramer: "Taking multichannel AFM images of electronic materials while they break"
Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
Stretchable conductors are of crucial relevance for emerging technologies such as wearable electronics, low-invasive bioelectronic implants or soft actuators for robotics.¹ Understanding of defect formation and deterioration of electronic properties of such materials during tensile strain cycles is important to optimize stretchable electronic materials.
Here we present an atomic force microscopy (AFM) method that provides multichannel images of surface morphology, conductivity, and elastic modulus during sample deformation. To develop the method, we investigate in detail the mechanical interactions between the AFM tip and a stretched, free-standing thin film sample. Our findings reveal the conditions to avoid artifacts related to sample bending modes or resonant excitations. As an example, we analyze strain effects in thin gold films deposited on a soft silicone substrate.² Our technique allows to observe the details of microcrack opening during tensile strain and their impact on local current transport and surface mechanics. We find that although the film fractures into separate fragments, at higher strain a current transport is sustained by a tunneling mechanism. The microscopic observation of local defect formation and their correlation to local conductivity will provide novel insight to design more robust and fatigue resistant stretchable conductors.³
AFM investigations on a thin film deposited on an elastic substrate during tensile strain. Three imaging modes are explored: height, conductivity and surface stiffness.
1. Decataldo, F. et al. Stretchable Low Impedance Electrodes for Bioelectronic Recording from Small Peripheral Nerves. Sci. Rep. 9, 1–9 (2019).
2. Cortelli, G. et al. Atomic Force Microscopy Nanomechanics of Hard Nanometer-Thick Films on Soft Substrates: Insights into Stretchable Conductors. ACS Appl. Nano Mater. 4, 8376–8382 (2021).
3. Cortelli, G. et al. In-situ force microscopy to investigate fracture in stretchable electronics: insights on local surface mechanics and conductivity, https://doi.org/10.48550/arXiv.2202.10119