# Dyadic Green's function formalism for photo-induced forces in tip-sample nanojunctions

## TL;DR

This paper develops a dyadic Green's function formalism to accurately model photo-induced forces in tip-sample nanojunctions, accounting for multiple scattering effects and substrate influence, aligning theoretical predictions with experimental observations.

## Contribution

It introduces a comprehensive dyadic Green's function approach that includes multiple scattering effects and substrate influence, improving upon previous simplified models.

## Key findings

- Substrate and tip anisotropy significantly affect force magnitude and spectrum.
- The model's predictions match experimentally measured photo-induced forces.
- Multiple scattering effects are crucial for accurate force estimation.

## Abstract

A comprehensive theoretical analysis of photo-induced forces in an illuminated nanojunction, formed between an atomic force microscopy tip and a sample, is presented. The formalism is valid within the dipolar approximation and includes multiple scattering effects between the tip, sample and a planar substrate through a dyadic Green's function approach. This physically intuitive description allows a detailed look at the quantitative contribution of multiple scattering effects to the measured photo-induced force, effects that are typically unaccounted for in simpler analytical models. Our findings show that the presence of the planar substrate and anisotropy of the tip have a substantial effect on the magnitude and the spectral response of the photo-induced force exerted on the tip. Unlike previous models, our calculations predict photo-induced forces that are within range of experimentally measured values in photo-induced force microscopy (PiFM) experiments.