Quasicontinuum simulations of geometric effect on onset plasticity of nano-scale patterned lines

Onset plasticity of metallic nano-lines or nano-beams is of considerable scientific and technological interest in micro-/nano- mechanics and interconnects of patterned lines in electronic devices, where capability of resistance to deformation is important. In this study, a multiscale quasicontinuum (QC) method was used to explore such an issue in a nano-scale copper (Cu) line protruding from a relatively large single crystal Cu substrate during compression. The results show that the yield stress of a rectangular beam on the substrate can be greatly reduced compared with that of a flat surface of the same area. For the rectangular line, the aspect ratio (width/height) affects dislocation morphology at the onset plasticity without much change of yield stress. However, for the trapezoidal line, the yield stress decreases with the base angle (alpha), especially when the a is over 54.7 degrees. As the sidewall orientation changes from < 100 > at alpha = 0 degrees, then to < 111 > at alpha = 54.7 degrees and finally to < 110 > at alpha = 90 degrees, a higher surface energy could enable easier dislocation formation and lower yield stress. Meanwhile, it is found that the interaction between the line and the support substrate also shows a great effect on yield stress. Moreover, although it is possible to open two extra dislocation slip planes inside from the two bottom corners of the Cu line with the alpha over 54.7 degrees, dislocation nucleation derived from them is only observed at alpha = 90 degrees.