Low-temperature scanning tunneling microscopy investigation of epitaxial growth of F16CuPc thin films on Ag(111)

In-situ low-temperature scanning tunneling microscopy (LT-STM) has been used to systematically investigate the epitaxial growth behaviors of copper hexadecafluorophthalocyanine (F16CuPc on Ag(111) from one monolayer to a few layers. At the monolayer regime, alternately arranged double-molecular-rows of F16CuPc form along the [1 (1) over bar0] direction of Ag(111). Within the same double-molecular-row, all F16CuPc molecules possess the same in-plane orientation. The growth in the second layer shows strong coverage dependence. At the initial growth stages of the second layer, isolated and rotated F16CuPc molecules pack along the [1 (1) over bar0] direction forming molecular dot-chains. Increasing the coverage leads to the appearance of densely packed and uniaxially oriented molecular nanoribbons comprising a few F16CuPc molecular rows packed exclusively along the [1 (1) over bar0] direction; this transits to a densely packed layer with all molecules having the same in-plane orientation. The growth of the third layer starts with the formation of densely packed molecular nanoribbons oriented along the [1 (1) over bar0] direction. Our results reveal that the growth of F16CuPc on Ag(111) adopts a layer-by-layer growth mode via pi-pi stacking with their molecular pi-plane oriented parallel to the substrate surface, stabilized through the interlayer dispersion forces.