Breaking strength tests on silicon and sapphire bondings for gravitational wave detectors

The realization of third-generation gravitational wave interferometric detectors is under way. An important improvement in detector sensitivity can be obtained with the reduction of thermal noise by reaching a cryogenic stage. Two materials have been identified to perform efficiently at low temperatures: silicon and sapphire. In this work the breaking strength of the silicate bonding that glues cylinders of silicon (Si) and sapphire (Al2O3) has been investigated. All material combinations, flatness quality and orientations have been tested over time. Breaking strength between Si-Si and Si-Al2O3 shows a value similar to that of fused silica, while Al2O3-Al2O3 does not seem to be a promising combination.