Charge carrier injection electroluminescence with CO functionalized tips on single molecular emitters

TL;DR

This study explores how CO-functionalized tips influence electroluminescence and photon mapping of single molecular emitters, revealing the role of tip state and surface effects in molecular photophysics.

Contribution

It demonstrates the impact of CO-functionalization on photon map resolution and contrast, and elucidates the charge injection mechanisms affecting electroluminescence.

Findings

CO-functionalization enhances photon map resolution and contrast.

Tip state significantly influences photon mapping.

Different substrate Fermi levels govern charge injection and excitation mechanisms.

Abstract

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force and light detection capabilities. Role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have a dramatic impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbital with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.