Resistance of grain boundary array to cleavage cracking in free-standing thin film

In a previous experimental study on free-standing silicon thin film, it was observed that cleavage front transmission across a through-thickness grain boundary could be considerably constrained by film surfaces. As a result, the boundary toughness was much lower than its bulk counterpart. In this study, inspired by the observation of crack front behaviors at triple grain boundary junctions, we perform a theoretical analysis on the fracture resistance of a regular grain boundary array in a thin film. The result indicates that as the cleavage front breaks down into a number of sections by the grain boundaries, the overall fracture resistance can be increased by nearly 60%. However, if the grain size is too small, the fracture resistance may decrease. The optimum grain size is around 1/5 to 1/4 of the film thickness. This finding provides a scientific basis for further experimental investigation on advanced processing techniques.