An electron acceptor molecule in a nanomesh: F4TCNQ on h-BN/Rh(111)

TL;DR

This study investigates how F4TCNQ molecules act as electron acceptors on h-BN/Rh(111), causing work function increases due to electron transfer, confirmed by experiments and density functional theory, revealing charge transfer and molecular mobility.

Contribution

It demonstrates the charge transfer and adsorption behavior of F4TCNQ on h-BN/Rh(111), combining experimental and theoretical insights into molecule-surface interactions.

Findings

Work function increases with molecular coverage.

Density functional theory predicts doubly charged F4TCNQ^{2-} in pores.

Molecules are mobile at room temperature, hopping between pores.

Abstract

The adsorption of molecules on surfaces affects the surface dipole and thus changes in the work function may be expected. The effect in change of work function is particularly strong if charge between substrate and adsorbate is involved. Here we report the deposition of a strong electron acceptor molecule, tetrafluorotetracyanoquinodimethane C$_{12}$F$_4$N$_4$ (F$_{4}$TCNQ) on a monolayer of hexagonal boron nitride nanomesh ($h$-BN on Rh(111)). The work function of the F$_{4}$TCNQ/$h$-BN/Rh system increases upon increasing molecular coverage. The magnitude of the effect indicates electron transfer from the substrate to the F$_{4}$TCNQ molecules. Density functional theory calculations confirm the work function shift and predict doubly charged F$_{4}$TCNQ$^{2-}$ in the nanomesh pores, where the $h$-BN is closest to the Rh substrate, and to have the largest binding energy there. The preferred adsorption in the pores is conjectured from a series of ultraviolet photoelectron spectroscopy data, where the $\sigma$ bands in the pores are first attenuated. Scanning tunneling microscopy measurements indicate that F$_{4}$TCNQ molecules on the nanomesh are mobile at room temperature, as "hopping" between neighboring pores is observed.