Direct observation of elastic strain and relaxation at a metal-metal interface by Auger electron diffraction: Cu/Ni(001)

Abstract

We have used Auger electron diffraction with high angular resolution to measure elastic strain at a pseudomorphic metal-metal interface. Shifts in the position of the $\mathrm{Cu} L_3{M}_{4,5}{M}_{4,5}$ Auger intensity maximum along the [101] direction betray expansion of the Cu lattice normal to the Cu/Ni(001) interface resulting from the Cu-Ni lattice mismatch. In the pseudomorphic regime (up to 14 Å of Cu), the Cu lattice constant perpendicular to the interface has been determined to be 3.71 ± 0.03 Å while the lattice constant is 3.52 Å in the plane of the interface (the lattice constant of Ni). Thus, the unit-cell volume of Cu is 46.0 ± 0.04 ${\mathrm{\AA }}^3$ in the pseudomorphic overlayer, compared to a bulk value of 47.0 ${\mathrm{\AA }}^3$. Above 14 Å, the lattice constant perpendicular to the interface drops as a result of dislocation generation and the relief of elastic strain. The critical coverage at which strain relief begins and the dependence of strain on coverage are in good agreement with simple classical models.