Effects of surface defects on surface stress of Cu(001) and Cu(111)

The effects of surface steps, adatoms, and two-dimensional islands on surface stress of Cu(001) and (111) surfaces are investigated using atomistic simulations. The approach employed to measure surface stresses is thermodynamically rigorous. The simulation results demonstrate that surface steps reduce the surface stress (provided that the step density is not too large), whereas surface adatoms either reduce or increase surface stress depending on the surface orientation. As the surface adatom density increases beyond a coverage of approximately 25%, the surface stress increases but returns to that of the singular surface as the coverage approaches a full monolayer. While it is not possible to create a very large adatom density on the surface (they rapidly combine to form islands), the highest adatom densities will likely occur during low temperature, high-rate growth. Addition of islands onto an otherwise flat surface has little effect on the surface stress. We provide a conceptual basis for understanding the effect of defects on surface stress in terms of local density ideas. The simulation results are compared with several experimental measurements on the evolution of film stresses during film growth.