The (001) surface of a single crystal of -Ga was investigated, by means of scanning tunnelling microscopy, under ultra-high vacuum conditions. It was found that the sputter-cleaned surface exhibited large, atomically flat, terraces which extended over distances of several hundreds of nm. On the atomic scale, the images revealed a (1 x 1) reconstruction of the surface. The measured step height, between the (001) terraces, provided direct evidence for the existence of molecular Ga2 dimers. It was pointed out that this was a long-standing assumption that had previously lacked clear experimental proof.

O.Züger, U.Dürig: Physical Review B 1992, 46[11], 7319-21