Analysis of electromagnetic forces and causality in electron microscopy

Area of Science:

• Physics
• Materials Science
• Nanotechnology

Background:

• Dielectric functions are crucial for modeling light-matter and electron-matter interactions.
• Non-causal dielectric functions can lead to unphysical results in simulations.
• Gold nanoparticles are widely used in various applications, including electron microscopy.

Purpose of the Study:

• To investigate the non-physical effects of non-causal dielectric functions on electron momentum transfer to gold nanoparticles.
• To introduce and apply a direct causality test based on surface Kramers-Kronig relations.
• To evaluate the suitability of different dielectric functions for describing gold nanostructures in electron microscopy.

Main Methods:

• Theoretical analysis of transverse momentum transfer.
• Development of a causality test using surface Kramers-Kronig relations.
• Application of the test to various dielectric functions for gold.

Main Results:

• Non-causal dielectric functions were shown to induce unphysical momentum transfer.
• The surface Kramers-Kronig relations provide a valid test for causality.
• Differences in dielectric functions significantly impact the simulated electron-nanoparticle interactions.

Conclusions:

• Causality is a critical consideration when selecting dielectric functions for simulating electron interactions with gold nanoparticles.
• The presented test offers a reliable method for ensuring the physical validity of dielectric models.
• Accurate dielectric functions are essential for precise modeling in electron microscopy of nanomaterials.