Moisture-assisted cracking and atomistic crack path meandering in oxidized hydrogenated amorphous silicon carbide films

Moisture-assisted cracking of silica-derived materials results from a stress-enhanced reaction between water molecules and moisture-sensitive Si-O-Si bonds at the crack tip. We report the moisture-assisted cracking of oxidized hydrogenated amorphous silicon carbide films (a-SiCO:H) consisting of both moisture-sensitive Si-O-Si bonds and moisture-insensitive bonds. The sensitivity of the films to moisture-assisted cracking was observed to increase with the Si-O-Si bond density, rho(Si-O-Si). This sensitivity was correlated with the number of Si-O-Si bonds ruptured, NSi-O-Si, through an atomistic kinetic fracture model. By comparing these correlated NSi-O-Si values with those estimated by a planar crack model, we demonstrated that at the atomistic scale the crack path meanders three-dimensionally so as to intercept the most Si-O-Si bonds. This atomistic crack path meandering was verified by a computational method based on graph theory and molecular dynamics. Our findings could provide a basis for better understanding of moisture-assisted cracking in materials consisting of other types of moisture-sensitive and moisture-insensitive bonds. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792212]