Structure of C70 layer on the Si(111)$$\sqrt 3 \times \sqrt 3 $$3×3-Ag Surface: STM Study

Adsorption of C70 molecules on the Si(111)\(\sqrt 3 \times \sqrt 3 \)-Ag surface and their monolayer ordering at room temperature were investigated by using a scanning tunneling microscope (STM). Islands of C70 molecules with close-packed hexagonal arrays were formed, growing from step edges or anti-phase domain boundaries of the substrate. Three different orientations of C70 molecular rows were identified, making angles of 0 ◦, 10.9 ◦, and approximately 30 ◦ with the main crystallographic direction of the Si(111)\(\sqrt 3 \times \sqrt 3 \)Ag surface. The 0 ◦ - and 10.9 ◦ -rotation domains are well registered to the substrate, suggesting a considerable molecule-substrate interaction. These domains are under compressive stress and thus populated with C70 molecules showing various STM contrasts. In comparison, the molecules in the ~ 30 ◦ -rotation domain interact weaker with the substrate and are subject to little stress. Thus the domain is populated with C70 molecules showing rather homogeneous STM contrasts.