Sexiphenyl on Cu(100): nc-AFM tip functionalization and identification

TL;DR

This study uses low-temperature STM and AFM with functionalized tips to analyze the adsorption and intra-molecular imaging of para-sexiphenyl molecules on Cu(100), enhancing understanding of tip-surface interactions and molecular identification.

Contribution

It demonstrates the use of CO-functionalized tips for high-resolution imaging of organic molecules on metal surfaces, expanding the database of molecular signatures for surface analysis.

Findings

6P molecules adopt a flat, rotated configuration on Cu(100)

CO-functionalized tips improve intra-molecular resolution

Tip characterization with adsorbed CO is effective

Abstract

The contrast obtained in scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images is determined by the tip termination and symmetry. Functionalizing the tip with a single metal atom, CO molecule or organic species has been shown to provide high spatial resolution and insights into tip-surface interactions. A topic where this concept is utilized is the adsorption of organic molecules at surfaces. With this work we aim to contribute to the growing database of organic molecules that allow assignment by intra-molecular imaging. We investigated the organic molecule para-sexiphenyl (C36H26, 6P) on Cu(100) using low-temperature STM and non-contact AFM with intra-molecular resolution. In the sub-monolayer regime we find a planar and flat adsorption with the 6P molecules rotated 10{\deg} off the <010> directions. In this configuration, four of the six phenyl rings occupy almost equivalent sites on the surface. The 6P molecules are further investigated with CO- functionalized tips, in comparison to a single-atom metal and 6P-terminated tip. We also show that the procedure of using adsorbed CO to characterize tips introduced by Hofmann et al. Phys. Rev. B 112 (2014) 066101 is useful when the tip is terminated with an organic molecule.