Experimental evidence for pseudomorphic growth of platinum on gold

Abstract

Bicrystal films of platinum on gold were prepared by evaporation in ultra-high vacuum. A shutter was moved across the substrate surface during the deposition of platinum so that platinum films in which there were thickness gradients were obtained. Examination of the specimens by transmission electron microscopy showed that platinum grew on gold approximately as a monolayer, and that the initial layers of platinum were strained in tension to exactly match the lattice of gold. When the thickness of the platinum exceeded about 10 Å, dislocations to accommodate part of the difference between the normal lattice parameters of platinum and gold were formed. As the deposit thickness increased further, a larger and larger fraction of the total misfit was accommodated by dislocations. These observations agree with theoretical predictions made by van der Merwe. The surface tensions of platinum and gold suggest that thin continuous films of platinum on gold are unstable, and that their energy would be lowered if they changed into three-dimensional platinum islands. Experimental evidence of this instability has been obtained.