Submonolayer growth of copper-phthalocyanine on Ag(111)

The growth of high-quality thin films is a key issue in the ability to design electronic devices based on organic materials and to tune their properties. In this context, the interfaces between metals and organic films play a decisive role. Here, we report on the interface formation between copper-phthalocyanine (CuPc) and an Ag(111) surface using various complementary methods. High-resolution low-energy electron diffraction revealed a rich phase diagram for this system with disordered (two-dimensional (2D)-gas-like) and ordered structures (commensurate and point-on-line). In particular, a continuous change in lattice parameters with increasing coverage was found for long-range ordered structures, indicating a substrate-mediated repulsive intermolecular interaction similar to the case of tin-phthalocyanine/Ag(111). Chemisorptive bonding to the substrate was found by x-ray standing waves and ultraviolet photoelectron spectroscopy, and this weakened with increasing coverage at low temperature. This remarkable effect is correlated to a shift in the highest occupied molecular orbital (HOMO) and a HOMO-1 split off band to higher binding energies. Based on our experimental results, we present a comprehensive study of the adsorption behavior of CuPc/Ag(111), including the mechanisms for phase formation and molecular interaction.