The growth of size-determined Cu clusters in nanometer holes on Au(111) due to a balance between surface and electrochemical energy

The electrochemical deposition of Cu clusters in nanometer-sized holes on A u(111) was observed by in-situ scanning tunneling microscopy (STM). The hol es were formed electrochemically by applying short negative voltage pulses to the STM tip prior to Cu deposition. The lateral extension of the cluster s is confined by the width of the holes. Their equilibrium height depends o n the applied overpotential rather than on the polarization time, reflectin g a delicate energy balance between the electrochemical energy and the enla rged surface energy of the growing Cu cluster. We attributed this to the fo rmation of steps at the size-confined Cu islands and derived a step formati on energy of 0.4-0.5 eV/(step atom). This is in good agreement with expecta tions for the formation energy of kinky steps on metal surfaces. (C) 1999 E lsevier Science S.A. All rights reserved.