Dislocation nucleation and propagation during thin film deposition under tension

Using molecular dynamics method, we study the nucleation of dislocations and their subsequent propagation during the deposition of tungsten thin films under tension. Aiming to reveal the generic mechanisms of dislocation nucleation during the deposition of polycrystalline thin films, the case of tungsten on a substrate of the same material is considered. The substrate is under uniaxial tension along the [111] direction, with the thermodynamically favored (01̄1) surface being horizontal. The simulation results indicate that the nucleation starts with a surface step, where a surface atom is pressed into the film along the [111̄] direction. This process leads to the generation of a half dislocation loop of Burgers vector 1/2 [111̄] along the (112) plane, which is about 73° from the horizontal plane. The dislocation propagates along the [3̄11] direction. As a result of the dislocation nucleation, a sharp surface step is eliminated.