NEAR-SURFACE BUCKLING IN STRAINED METAL OVERLAYER SYSTEMS

Scanning tunneling microscopy (STM) images of Ag films grown on Ru(000 1) reveal a periodic unit cell with a structural transformation at sil ver coverages slightly less than one monolayer. Dislocations in the ov erlayers are similar to the Au(111) herringbone structure; however, Ag /Ru(0001) exhibits two novel differences from previously observed herr ingbone structures. First, the unit cell dimensions change dramaticall y as a function of coverage. Second, STM images of Ag/Ru(0001) are inv erted relative to those for Au(111). We show that this image inversion is due to substantial relaxations perpendicular to the surface result ing from local strains in the silver overlayer.