Submonolayer growth of copper-phthalocyanine on Ag(111)

Ingo Kröger,Tien-Lin Lee,Mario Kochler,Johannes Ziroff,Andreas Stahl,Florian Pollinger,Benjamin Stadtmüller,Jörg Zegenhagen,Christoph Stadler,Christian Kumpf,Friedrich Reinert

doi:10.1088/1367-2630/12/8/083038

Abstract

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.

Highlights

Of substrate–molecule and molecule–molecule interactions, π-conjugated molecules show a diversity of phases that can strongly depend on coverage, temperature, substrate and film preparation parameters [1, 2], as well as the shape of the molecule and possible reactive side groups
The highest occupied molecular orbital (HOMO)-1 level is located at a binding energy of 2.16 eV and shows an additional feature at 1.79 eV, which we identify as a HOMO-1 split off (SO) band
The adsorption of CuPc molecules and the formation of a variety of lateral structures can be understood as the result of a minimization of the interface potential energy, under some specific boundary conditions

Summary

Introduction

Of substrate–molecule and molecule–molecule interactions, π-conjugated molecules show a diversity of phases that can strongly depend on coverage, temperature, substrate and film preparation parameters [1, 2], as well as the shape of the molecule and possible reactive side groups. A systematically studied prototype for these kinds of model systems is 3,4,9,10-perylene tetracarboxylicacid-dianhydride (PTCDA) on Ag(111) (see [1], [3]–[9] and references therein)

Results

Discussion

Conclusion