Initial Growth of N,N′‑Bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxdiimide Films on Cu(100)

We have studied the initial stages of the adsorption of N,N′-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxdiimide (EP-PTCDI) on Cu(100) using scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. STM images show that the EP-PTCDI molecules initially absorb on the surface, forming ordered islands, without preferential nucleation at the step-edges of the terraces as is the case for adsorption of the same molecule on Ag(111). The 2D islands grow upon the completion of the surface with a single-molecular layer. The experimental and simulated LEED patterns show that the molecular arrangement within the islands can be explained by a commensurate superstructure and its four rotational equivalents. The electron spectroscopies show net charge transfer from the surface to the molecule and a decrease of about 0.7 eV in the work function (from 4.59 to 3.9 eV) after a single-layer adsorption. The DFT calculations for the adsorption of a single layer qualitatively reproduce the features observed in STM images and allow us to explain the observed charge exchange behavior together with the work function change.