Island equilibrium shape and shape fluctuations on the reconstructed Au(1 0 0) surface

Islands and vacancy islands are produced on the Au(1 0 0) surface by deposition of submonolayer quantities of gold and by argon ion sputtering, respectively. As noted before, these islands have a rectangular shape with the long side oriented along the long base vector of the 5 × n (n ≈ 25) unit mesh of the reconstructed Au(1 0 0) surface. The initial (aspect) ratio of the long to the short side is about 10. During coarsening over a period of hours at about 350 K, the aspect ratio shrinks gradually to a value of about 1. At this stage, the aspect ratio varies stochastically around a mean value, is, however, still determined by the growth/decay conditions. Islands which neither grow or decay over a very long period in time have an aspect ratio of about 1, which is thus considered to be the approximate aspect ratio of the equilibrium shape. Island edges oriented along the long base vector of the reconstructed surface are mostly straight. Occasionally macro-kinks with a length of one unit vector of the reconstructed mesh are observed. The equilibrium shape fluctuations of the islands are evaluated in terms of the step line tension. A mean value of 170 meV per atom length is obtained. This number is about a factor of 3 larger than the step line tension on the unreconstructed Au(1 0 0) surface in an electrolyte, however lower than the step line tension on Cu(1 0 0) in vacuum.