A Quest for the Mechanism of Ultrahigh Resolution SEM Imaging

Area of Science:

• Materials Science
• Surface Science
• Microscopy

Background:

• Conventional scanning electron microscopy (SEM) theory posits SE1 electrons define resolution, while SE2 electrons contribute to background noise.
• Quantitative links between SE1/SE2 emission and spatial resolution remain unclear due to undefined simulation parameters.

Purpose of the Study:

• To establish unambiguous definitions for SE1 and SE2 electrons within a Monte Carlo simulation framework.
• To investigate the emission characteristics and impact of SE1 and SE2 electrons on spatial resolution in SEM.

Main Methods:

• Development of a comprehensive simulation framework with precise SE1/SE2 definitions.
• Simulation of secondary electron emission from solid materials using a primary beam ranging from 0.1 to 30 keV.
• Analysis of electron emission modulation by local 3D surface morphology.

Main Results:

• SE1 and SE2 electrons share similar emission characteristics, differing primarily in spatial spread.
• Local 3D surface morphology significantly modulates SE2 electron emission patterns.
• Simulations of gold nanoparticles on carbon substrates demonstrated morphology-modulated SE2 electrons contribute to sub-nanometer resolution (~0.8 nm).

Conclusions:

• The study overturns the traditional view that SE2 electrons degrade image resolution.
• A unified physical explanation for ultrahigh-resolution SEM imaging mechanisms is provided.
• Surface morphology's role in secondary electron emission and its contribution to high-resolution imaging are highlighted.