Structure of C70 layer on the Si(111) √3 x √3-Ag Surface: STM Study

Adsorption of C70 molecules on the Si(111) v 3 x v 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) v 3x v 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.