STM images and the corresponding diagrams of Co islands grown along pseudo- and pseudo-[1-100] directions. (a)10 × 10-nm2 STM images showing Co-(11-20)-2 × 2 islands growing along the pseudo-[1-100] direction, and (b) the pseudo- direction. The black lines represent the rows in the topmost bilayers while the white lines refer to the rows in the underlying layers. Corresponding schematic diagrams are shown in (c) and (d), respectively. The filled circles refer to the protrusions in the topmost bilayer, while the open circles represent the atomic protrusions in the underlying bilayers.