Nanoscale Ductile Deformation by Nanoscratch Test at Extremely Low Load of Brittle Materials

It is well-known that the nanoscale structures on materials can improve mechanical properties. Since it is difficult to make nanoscale structures by mechanical deformation, a few brittle materials are used for nanoscale structures using lithography and etching. However, previous researches empirically showed that brittle materials behaved as if they were ductile materials under extremely low force. No brittle fracture but ductile deformation occurred even when they were scratched with sharp tips. The previous studies, however, showed only phenomena and no quantitative studies on ductile deformation. In this study, we applied the extremely low force on a few brittle materials such as single-crystal silicon, germanium and gallium-arsenide using a nanoscratch tester, analyzed mechanical behavior of the ductile deformation, and determined the transition point of the ductile deformation and the brittle fracture. First, we measured the lateral force and depth while applying the linear increasing normal force through moving a sharp tip along the lateral direction. The ductile deformation occurred at extremely low force and the first brittle fracture occurred in the brittle materials over a certain force varying according to the brittle materials. The variation of the forces is related to the mechanical properties, such as the toughness, fracture strength, and elasticity. The rapid change of lateral force was observed when the first brittle fracture occurred, which meant that the transition point could be determined by observing the change of lateral force. Finally, nanoscale structures were made on the brittle materials by ductile deformation, and we verified that the nanoscale structures can be made on brittle materials based on mechanical deformation.