Field modeling and ray-tracing of a miniature scanning electron microscope beam column

Area of Science:

• Physics
• Materials Science
• Engineering

Background:

• Scanning electron microscopes (SEM) require precise focusing columns for high-resolution imaging.
• Operation in extreme environments, like the lunar surface, necessitates miniaturized and robust components.
• Previous designs may not meet the stringent requirements for extraterrestrial applications.

Purpose of the Study:

• To introduce a novel miniature SEM focusing column design.
• To assess the potential performance of this design for lunar surface applications.
• To analyze key parameters affecting probe radius and identify sources of aberration.

Main Methods:

• Development of a focusing column by NASA Marshall Space Flight Center and Advanced Research Systems.
• Electrostatic field modeling using the Boundary Element Method (BEM) for complex electrode shapes.
• Fourier series solution for lens field accuracy enhancement, enabling precise ray-trace analysis.
• Estimation of probe radius parameters including source size, aberrations, diffraction, and space charge broadening.

Main Results:

• The BEM and Fourier series approach provided accurate electrostatic field modeling.
• Ray-trace analysis allowed for the assessment of geometric aberrations.
• Key parameters influencing probe radius were estimated, providing insights into potential resolution limits.
• Two distinct operational modes with different lens field solutions were identified.

Conclusions:

• The designed miniature SEM focusing column shows potential for lunar surface applications.
• The combined BEM and Fourier series method is effective for analyzing electron lens systems.
• Further optimization based on aberration analysis can enhance imaging performance for extraterrestrial SEMs.