# Tip-Enhanced Raman Images of Realistic Systems through Ab Initio Modeling

## TL;DR

This paper shows how substrate effects impact TERS imaging accuracy using realistic simulations.

## Contribution

A new periodic first-principles simulation method reveals how substrates affect TERS image accuracy.

## Key findings

- Ignoring substrates in TERS simulations leads to deviations from experimental data.
- Periodic simulations better capture TERS images of defective MoS2 and Mg(II)-porphine on Ag(100).
- Surface interactions strongly influence out-of-plane vibrational mode images in TERS.

## Abstract

Tip-enhanced Raman spectroscopy (TERS) is a powerful
method for
imaging vibrational motion and chemically characterizing surface-bound
systems. Theoretical simulations of TERS images often consider systems
in isolation, ignoring any substrate support, such as metallic surfaces.
Here, we show that this omission leads to deviations from experimentally
measured data, as demonstrated by simulations with a new finite-field
periodic formulation of first-principles simulation of TERS spectra
that can address extended systems. We show that TERS images of defective
MoS2 monolayers calculated using cluster models are qualitatively
different from those calculated when accounting for the periodicity
of the substrate. For Mg­(II)-porphine on Ag(100), a system for which
a direct experimental comparison is possible, these simulations prove
to be crucial for explaining the spatial variation of TERS intensity
patterns and allow us to uncover fundamental principles of TERS spectroscopy.
We explain how and why surface interactions affect images of out-of-plane
vibrational modes much more strongly than those of in-plane modes,
thereby providing an important tool for the future interpretation
of these images in more complex systems.