Considerable interest exists in the physical properties of ultra-thin metal films.
Particular interest in magnetic systems has resulted from novel magnetic behavior predicted and observed in the few monolayer regime. In analogy to band-gap engineering in strained layer epitaxy in semiconductors, one can exploit the dependence of the exchange energy on lattice expansion in epitaxial metal films to produce new magnetic phases not found to occur naturally. Such atomic engineering of low dimensional magnetic systems has only recently been realized. The preferential nucleation results from the structural imperfections at the bulged corners of the herringbone reconstruction. The grey scale cycles twice through the image to enhance contrast.