Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine

TL;DR

This study investigates how ZnPc molecules interact electronically with Pt(111) surfaces, both clean and iodated, revealing how iodine modifies charge transfer and molecular orientation at the interface.

Contribution

It provides detailed insights into the site-dependent charge transfer mechanisms and the influence of iodine on the molecular configuration and electronic properties at the Pt(111)-ZnPc interface.

Findings

ZnPc lies nearly parallel to Pt(111) at low coverage due to Zn-Pt attraction.

Iodine pre-deposition prevents Zn-Pt attraction, resulting in more uniform charge distribution.

ZnPc becomes decoupled from Pt after the second layer, with iodine acting as an electron acceptor dopant.

Abstract

The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM). Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I $\left(\sqrt{3}\times\sqrt{3}\right)$ or Pt(111)-I $\left(\sqrt{7}\times\sqrt{7}\right)$, and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.