OBSERVATION OF AN ADLAYER-DRIVEN SUBSTRATE RECONSTRUCTION IN CU-PT(111)

An unusual strain relaxation mechanism has been observed during the growth of ultrathin Cu films on Pt~111! at a substrate temperature of 450 K. After the completion of a pseudomorphic first Cu monolayer, the Pt substrate undergoes a reconstruction which is visible in the pseudomorphic Cu overlayer. Using in situ helium atom scattering, interlayer mass transport is observed as ad-atoms are incorporated into the substrate. Scanning tunneling microscopy measurements allow us to label the substrate reconstruction as being similar in nature to the ‘‘star’’ network of the reconstructed Pt ~111! surface. @S0163-1829~98!52840-8# Heteroepitaxial growth in systems without an exact lattice match gives rise to strain in the growing film. The magnitude of the strain increases in proportion to the number of layers in the film and ultimately, it determines the maximum thickness of a pseudomorphic structure. A number of mechanisms for strain relief in metal-film growth have been observed recently ~see, for instance, Refs. 1 and 2!. Dislocation networks and/or reconstructions have been seen in thin growing films, while thicker films often exist as floating overlayers with isotropic relaxation. These observations broadly agree with the expectations from early theoretical models, 3,4 which