Figure 5 Empty-state STM images showing Ni-containing structures. (a) Hexagonal island on Ge(111)-c(2 × 8) surface. (b) Hexagonal island on Ag/Ge(111)-√3 × √3 surfaces. (c) 7 × 7 island on Ge(111)-c(2 × 8) surface. (d) 7 × 7 island on Ag/Ge(111)-√3 × √3 surfaces. The notations in left upper corners represent the specified structures. First, we focus on the structures typical Foretinib manufacturer of the Ni/Ge(111)-c(2 × 8) surface.

They are presented in Figure 3 along with proposed schematics of the structural models. The models are drawn on a background of the Ge(111)-c(2 × 8) lattice. Figure 3a is a small-scale empty-state STM image showing ring-like defects. By analyzing a number of images, we have found that the structures emerge in single, dimer, or trimer configuration. In an attempt to explain the origin Salubrinal mouse of the structures, we shall recall that ring-like clusters frequently develop after annealing the Si(111) surfaces

containing trace amounts of Ni [1], Co [3], and Fe [6]. Depending on the adsorption system, the authors ascribed the rings to precursors to either metal-induced reconstruction of the substrate surface or metal-containing islands which grow on the substrate surface. The ring-like defects, however, were not reported on the Co/Ge(111)-c(2 × 8) surface [10]. By referring the STM image to the structural model of the Ge(111)-c(2 × 8) (Figure 3a), we notice that the rings are likely to represent missing Ge adatoms. In filled-state images, however, the rings are brighter in contrast to the substrate. This effect is particularly distinct for the sample bias -0.6 V at which no local density of states exists for the Ge(111)-c(2 second × 8) surface (see inset in Figure 3a). This observation leads us to conclude that the ring-like defects are more likely to belong to Ni atoms sitting at Ge atom positions rather than represent missing adatoms. Besides the ring-like defects, annealing the Ni/Ge(111)-c(2 × 8) surface produces flat-topped

islands with atomically resolved corrugations, forming a 2√7 × 2√7 pattern (islands enclosed with solid circles in Figure 3b) and a 3 × 3 pattern (in Figure 3b, the island enclosed with a dotted circle). The islands typically have a height within the range from 0.15 to 0.2 nm and adopt approximately triangular, hexagonal, and trapezoidal shapes. However, a few islands are observed with irregular shapes. The islands with the 3 × 3 are observed at higher densities as compared to their Ro 61-8048 clinical trial counterparts. The distances between the islands and ring-like objects as well as their location on the surface are random. More detailed features of the different islands are shown in the insets in Figure 3b as well as in Figure 3c. We shall notice that both islands have empty-state images markedly different from the filled-state ones. This indicates that the islands have semiconducting properties rather than metallic.