In situ scanning tunneling microscopy of bismuth electrodeposition on Au(111) surfaces

The underpotential deposition (UPD) and overpotential deposition (OPD) of bismuth on Au(1 1 1) have been studied with in situ scanning tunneling microscopy (STM). Large area STM images obtained in the UPD region indicate that adsorbed bismuth lifts the reconstruction of the Au(I 1 1) surface. This results in the formation of gold islands at potentials less than 0.170 V-SCE. In situ STM images of the Bi OPD process reveal needle growth across the gold surface, beginning at step edges and proceeding to form relatively uniform films. This growth behavior is observed at -0.070 V-SCE, after stepping the potential to -0.120 V-SCE for 4 s. Atomic resolution images of the OPD bismuth layer indicate that the unit cell is nearly rectangular with dimensions of 3.9 +/- 0.2 and 4.3 +/- 0.2 Angstrom. This corresponds to having the shorter side of the Bi unit cell along the long edge of the bismuth needles. The reduced spacing hinders the incorporation of atoms diffusing along these edges. Instead, diffusing atoms become incorporated at the needle end where the structure is more open, resulting in the observed Bi growth anisotropy. (C) 2002 Elsevier Science B.V. All rights reserved.