An attempt was made to settle the controversy as to whether surface dimers in the (001) surface were intrinsically symmetrical or asymmetrical. Atom-resolved scanning tunnelling microscopic images of a low (about 1%) defect density surface at 144K furnished definite evidence for the asymmetrical dimer model. A local effect of surface defects upon the buckling of dimers at low temperatures was identified, which had not been clear in previous scanning tunnelling microscopic observations at 120K.

H.Tochihara, T.Amakusa, M.Iwatsuki: Physical Review B, 1994, 50[16], 12262-5