The decay characteristics of three-dimensional (3D) islands formed on surfa
ces are investigated theoretically considering two types of interlayer mass
transport mechanisms. If an adatom on a given layer can easily descend fro
m any site along the periphery of the layer, an optimal island slope and a
constant terrace width will be selected during the decay. In contrast,if th
e adatom can descend primarily through selective (such as kinked) sites, th
e decay will be accompanied by a gradual increase in the island slope. Thes
e generic conclusions provide the basis for a microscopic understanding of
the decay of nanostructures in fcc(111) and fcc(100) metal homoepitaxy and
are applicable to other systems as well.