Molecular dynamics study on the nanoimprint of copper

Molecular dynamics simulations using the embedded atom method (EAM) potential are carried out to study the nanoimprint of copper single crystal. The effects of mould taper angle, mould tooth spacing and crystal orientation on the deformation behaviour, dislocation movement and imprint force are investigated. A four-stage deformation is observed for the mould with a small taper angle, while it cannot be clearly identified for the mould with a large taper angle. The four-stage deformation is: (1) a purely elastic deformation with a rapid increase of imprint force, (2) dislocation nucleation with a small drop of imprint force, (3) local pile-up of dislocations with a second rapid increase of imprint force, and (4) active dislocation movement with almost a plateau of imprint force. Among the three imprint surfaces of (0 0 1), (1 1 0) and (1 1 1), it is found that the (0 0 1) surface results in the lowest imprint force and the (1 1 1) surface results in the highest one. It is also observed that the pattern transfer on the (1 1 1) surface is less accurate than on the (0 0 1) and (1 1 0) surfaces. It is shown that the smaller the mould tooth spacing, the stronger is the interaction of the stress fields in the substrate, which results in more obvious influence on the material deformation, the dislocation movement and the imprint force.