Fracture behavior of diamondlike carbon films deposited on polymer substrates

Abstract

The authors investigated the fracture behavior of diamondlike carbon films deposited on polyethylene terephthalate substrates using two types of film synthesized under different sputtering-gas pressure conditions. Specifically, the influence of the hardness, indentation Young's modulus, and scratch toughness on the multiple cracking behavior of the films was explored. Based on microscratch and nanoindentation experiments, it was found that the sputtering-gas pressure conditions played an important role in the chemical composition and concomitant changes in the mechanical properties of the diamondlike carbon films. In particular, higher gas pressure conditions resulted in a lower hardness, indentation Young's modulus, and scratch toughness, which are presumably due to the presence of a large number of C–O bonds in the diamondlike carbon structure. In situ observations during tensile-loading experiments in conjunction with multiple crack analyses showed that the films synthesized under higher gas pressure conditions exhibited a high level of crack resistance to externally applied tensile strain. The estimated crack onset strain, i.e., the strain at which the first crack was generated, was approximately 2%, which is about 1.3 times higher than that for the diamondlike carbon films synthesized under lower gas pressure conditions.