Phase separation on an atomic scale: The formation of a novel quasiperiodic 2D structure

Scanning tunneling microscopy of a "5×5"-Cu/Si(111) ordered layer reveals an unusual type of quasiperiodic phase. Topographic and spectroscopic images together with their Fourier analysis reveal at least three electronically and structurally distinct local phases which arrange to form a quasiperiodically ordered structure. The nature and origin of this novel structure is discussed. © 1989 The American Physical Society.