Anisotropic profile decay on perturbed Au(111) vicinal surfaces

The anisotropy of the surface free energy has a large influence on the decay rate of periodic surface profiles at temperatures below the roughening temperature This has been demonstrated by a study of the periodic surface profiles that were etched into vicinal Au(111) crystals in two orientations: with their wavevector parallel (psi = 0) and perpendicular (psi = pi/2) to the intrinsic step direction of the vicinal surface. Due to this modulation, steps become either oscillatory in shape or remain straight with their average separation modulated. Accordingly, profile decay is driven primarily by step self-energy (psi = 0) or step interaction energy (psi = pi/2). The rate of decay was measured under ultra-high vacuum conditions at 750 degrees C using a scanning tunneling microscope for imaging. A large anisotropy of decay was observed on two vicinal crystals of 1.5 and 5 degrees miscut, with the psi = 0 decay being much faster than with psi = pi/2. The results are evaluated and discussed in the framework of recent theory.