AN STM INVESTIGATION OF THE CU(110)-C(6X2)O SYSTEM

The formation of the c(6 x 2)-O phase on a Cu(110) surface, after completion of the (2 x 1)-O structure, was observed by scanning tunneling microscopy (STM). The phase is composed of isotropic structural elements on fourfold hollow sites of the substrate lattice, which form a quasi-hexagonal array and manifest themselves as large protrusions in the STM images. Individual units of this type are mobile and also represent stable nuclei within a (2 x 1) surrounding. Nucleation is activated and occurs preferentially at steps, in contrast to previous findings with the (2 x 1) phase. Structural implications of additional weak features in high resolution images and of the observed change in two-dimensional density of Cu atoms are discussed.