Interface strength of structured nanocolumns grown by glancing angle deposition

In order to investigate the mechanics of interfacial fracture in structured nano-elements grown by glancing angle deposition (GLAD), fracture experiments were conducted on oblique Ti nanocolumns grown on a Si substrate using a micro-brick specimen. Two types of specimens, a Forward specimen (loading with the column tilt direction) and a Reverse specimen (loading against the column tilt), were prepared to clarify the effect of an asymmetric nanostructure on the interface strength. The specimens fractured at the interface or near the interface between the Ti nanocolumns and the Si substrate for both specimens. The critical force and displacement at fracture in the Forward specimens were about 2.0 times and 1.6 times as large as those in the Reverse specimens, respectively, showing clear anisotropy in the interface strength. The local stress distribution along the interface in the single nanocolumn at fracture was analyzed by finite element analysis. While the stress singularity in the Reverse specimen was greater than that in the Forward specimen, the normal stresses in a region 1–3 nm near the interface edge were almost identical regardless of the loading direction, suggesting that intensified stress in the nanoscale region dominated fracture.