Cohesive zone models to understand the interface mechanics of thin film transfer printing

Abstract

Competing fracture in the transfer of thin films from a relatively rigid host substrate to a flexible polymer substrate is studied using finite element simulations with cohesive zone models. Cohesive zone models for delamination based on traction-separation relations with a maximum stress criterion for damage initiation and mode-independent fracture energy for complete separation are explored to identify important parameters that affect transfer printing. Successful transfer of a thin film to a relatively compliant polymer substrate from a stiffer substrate depends on relative crack lengths, interface strengths, and fracture energies. Interface selection occurs where the mode-mix at the crack tip is predominantly due to normal stresses, despite the interface toughness being mode-independent. The observations and the fracture maps developed here predict the interface selection directly with material properties of the interfaces, substrates, and films.