Nanoscale observation of initial stages of Cd-electrodeposition on Au(111)

The initial stages of Cd-electrodeposition on a Au(111) surface from sulfuric acid solution were investigated by means of an electrochemical scanning tunnelling microscope (EC-STM). High resolution images were obtained over a potential range between 1050 and -10 mV vs. the Nernst potential for Cd bulk deposition, E-0(Cd/Cd2+). The presented results show that in cadmium containing sulfuric acid electrolyte the Au(111) surface starts to reconstruct at potentials around 850 mV vs. E-0(Cd/Cd2+). First signs of Cd nucleation become observable between 350 and 300 mV as distinctively separated islands of monoatomic height. These islands preferably nucleate not as expected on step edges but show alignment with respect to the underlying substrate. Further cathodic polarisation leads to formation of strings and finally to a closed layer of deposited cadmium in a potential region where interfacial alloying is expected to appear. A second deposited layer nucleates with a different morphology and forms another atomically flat topography slightly negative of E-0(Cd/Cd2+), reproducing the morphology of the underlying substrate. (C) 2003 Elsevier Science B.V. All rights reserved.