Scanning tunneling microscopy of defects in quasiperiodically ordered surfaces

We demonstrate that the limited coherence length of a one-dimensional quasiperiodically ordered superstructure of a thin Ag film on GaAs(1 1 0) surfaces is due to structural defects. We identify dislocations, phason defects, and domain walls. The domain walls end at dislocations, whose stress field is found to induce a wide distribution of oriented phason defects.