In-situ force microscopy to investigate fracture in stretchable electronics: insights on local surface mechanics and conductivity

TL;DR

This paper introduces a novel AFM-based method to simultaneously image surface morphology, conductivity, and elastic modulus in stretchable conductors during deformation, revealing defect formation and fracture mechanisms at the microscale.

Contribution

The study develops a multichannel AFM technique for in-situ analysis of mechanical and electrical properties during stretching, providing new insights into fracture processes in stretchable electronics.

Findings

Microcrack opening observed during tensile strain.

Current transport persists via tunneling at high strain.

Method avoids artifacts from sample bending or resonance.

Abstract

Stretchable conductors are of crucial relevance for emerging technologies such as wearable electronics, low-invasive bioelectronic implants or soft actuators for robotics. A critical issue for their development regards the understanding of defect formation and fracture of conducting pathways during stress-strain cycles. Here we present a novel 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. 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.