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. The 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 an 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 orbitals 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.

Faculty of Mathematics and Physics Charles University Prague 180 00 Czech Republic

Faculty of Nuclear Sciences and Physical Engineering Czech Technical University Prague Prague 115 19 Czech Republic

Institute of Physics Czech Academy of Sciences Prague 162 00 Czech Republic

Instituto de Ciencia de Materiales de Madrid CSIC Sor Juana Inés de la Cruz 3 E28049 Madrid Spain

Instituto de Física Fundamental CSIC Serrano 121 E28006 Madrid Spain

Regional Center for Advanced Materials and Technologies Olomouc 78371 Czech Republic

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