Strain Relaxation in Hexagonally Close-Packed Metal-Metal Interfaces.

Scanning tunneling microscopy observations on epitaxial Cu/Ru(0001) show the relaxation of (tensile) lattice strain to occur in four different stages with increasing film thickness, from pseudomorphic to unilaterally contracted to (quasi-)isotropically contracted film structures, with decreasing lattice strain and increasing interface energy. The underlying film layers rearrange during growth. Comparison with other data suggests this scheme to be more generally valid for tensile and, with slight modifications, also compressive strain relaxation in hexagonally close-packed metal surfaces and metal-metal interfaces.