In situ STM studies on underpotential deposition of Sn on Au(100)

We present in situ STM studies on Sn electrodeposition on Au(100) surfaces at underpotentials. The Sn under potential deposition (UPD) on Au(100) proc eeds in three stages: the reversible submonolayer UPD; surface alloying; an d alloying that extends to the bulk. The formation of the reversible submon olayer UPD proceeds in the form of clusters of similar to2 nm. at potential s as early as 0.04 V. The surface alloying takes place at -0.04 V, which is evidenced by sudden immersion of the Sn clusters as well as significant ch anges of steps on the surface. The bulk alloying sets in at -0.3 V, which l eads to rapid change of the surface morphology. The earlier set in of the s urface and bulk alloying process is considered the result of enhanced inter diffusion of Sn and Au atoms upon decreasing the potential. It has been sho wn that Sn UPD on Au(100) is much more complex than that of other metal UPD systems studied previously by electrochemical scanning tunnelling microsco py, but it serves as a good system for all-sided studies of the UPD process es. Copyright (C) 2001 John Wiley & Sons, Ltd.