resolution of electronic and vibronic states of TCNQ

The electronic structure of molecules on metal surfaces is largely determined by hybridization and screening by the substrate electrons. As a result, the energy levels are significantly broadened and molecular properties, such as vibrations are hidden within the spectral line shapes. Insertion of thin decoupling layers reduces the line widths and may give access to the resolution of electronic and vibronic states of an almost isolated molecule. Here, we use scanning tunneling microscopy and spectroscopy to show that a single layer of MoS2 on Ag(111) exhibits a semiconducting bandgap, which may prevent molecular states from strong interactions with the metal substrate. We show that the lowest unoccupied molecular orbital (LUMO) of tetracyanoquinodimethane (TCNQ) molecules is significantly narrower than on the bare substrate and that it is accompanied by a characteristic satellite structure. Employing simple calculations within the Franck–Condon model, we reveal their vibronic origin and identify the modes with strong electron–phonon coupling

Structural and Electronic Properties of Organic Molecules on Monolayer Molybdenum Disulfide on Ag(111)

Molecular charge transfer complexes are an interesting class of materials due to their promising applications in molecular electronic devices. Understanding the charge transfer between donor and acceptor molecules at the nanoscale is crucial for the ongoing development and optimization of those devices. In this thesis, we investigate charge-transfer processes within prototype mixed molecular systems on the singlelayer molybdenum disulfide (SL-MoS2) on Ag(111). The characterization of molecules on SL-MoS2 is motivated by the fact that SL-MoS2 electronically decouples molecules from the metal substrate and enables us to resolve the electronic properties (vibronic states and charge transfer processes) of an almost isolated molecule. Spectroscopic measurements of SL-MoS2 on Ag(111) reveal the semiconducting bandgap. We also observe a moiré pattern due to the lattice mismatch between SL-MoS2 and Ag(111)