On the mechanism of rapid mound decay

The observation of rapid mound decay events on Ag(lll) is reported. As in the case of Cu(lll), the critical terrace width for the onset of the rapid decay corresponds to about six atom rows. For Ag(lll), this distance is incompatible with the surface state model proposed earlier for Cu(lll). A new mechanism for the rapid decay events is considered, which involves steps in close proximity. It is shown that the observed mean terrace width in the final, rapid decay of a mound is well described by a combination of the random walk and shape fluctuations of the islands with the proposed local decay mechanism. Approximate activation energies for the new process are determined for Cu(lll) and Ag(lll). (C) 2000 Elsevier Science B.V. All rights reserved.