Submolecular resolution by variation of IETS amplitude and its relation to AFM/STM signal

TL;DR

This study demonstrates that high-resolution submolecular imaging in STM, AFM, and IETS is due to the lateral bending of a CO tip, with IETS contrast influenced by vibrational frequency shifts and amplitude variations, supported by simulations.

Contribution

It introduces an extended probe-particle model that accounts for vibrational frequency renormalization and amplitude variation to explain high-resolution IETS contrast.

Findings

High-resolution contrast arises from CO tip bending.

IETS contrast involves vibrational frequency shifts and amplitude changes.

Simulations confirm the imaging mechanism and response of CO modes.

Abstract

Here we show scanning tunnelling microscopy (STM), non-contact atomic force microscopy (AFM) and inelastic electron tunnelling spectroscopy (IETS) measurements on organic molecule with a CO- terminated tip at 5K. The high-resolution contrast observed simultaneously in all channels unam- biguously demonstrates the common imaging mechanism in STM/AFM/IETS, related to the lateral bending of the CO-functionalized tip. The IETS spectroscopy reveals that the submolecular con- trast at 5K consists of both renormalization of vibrational frequency and variation of the amplitude of IETS signal. This finding is also corroborated by first principles simulations. We extend accord- ingly the probe-particle AFM/STM/IETS model to include these two main ingredients necessary to reproduce the high-resolution IETS contrast. We also employ the first principles simulations to get more insight into different response of frustrated translation and rotational modes of CO-tip during imaging.