A low-temperature scanning tunnelling microscope was used to observe a single-dimer vacancy (A-type defect) which produced buckling of the dimers on a (001) surface at temperatures near to 200K. This dimer buckling always occurred in rows which were adjacent to the A-type defects, which simultaneously formed an out-of-phase boundary in the domain of a c(4 x 2) structure. However, the out-of-phase boundaries around the A-type defects disappeared from the surface at 78K.

T.Yokoyama, K.Takayanagi: Physical Review B, 1997, 56[16], 10483-7