Development of In situ TEM Experiment of Crack Initiation at Interface Edge in Nano-Structures

A novel in situ TEM fracture testing method is developed to elucidate the mechanics dominating crack initiation at an interface edge in nano-structures. The testing system includes a special mechanical apparatus equipped with a piezo-actuated stage and a diamond loading tip attached to a MEMS load sensor, which enables us to control specimen position and perform quantitative load measurement with enough precision. Nano-scale cantilever specimens with interfaces are fabricated from a multi-layered material (Si/Cu/SiN) using FIB process technique. The validity of the testing method is demonstrated by conducting interfacial crack initiation experiments for the specimens with different size. The applied load and the specimen image have been successfully monitored and recorded during the experiments. For each specimen, the crack is initiated from the free-edge of interface between Si/Cu at a maximum load, Pc, and the specimen is instantly separated at the interface. Using the experimental results the stress fields along the Si/Cu interface at the crack initiation are analyzed for each specimen by finite element method. This reveals that the crack initiation of the Si/Cu interface is governed by the normal stress on the interface near the edge.