Caustic imaging of gallium droplets using mirror electron microscopy.

Area of Science:

• Surface Science
• Electron Microscopy
• Materials Characterization

Background:

• Mirror Electron Microscopy (MEM) is a technique sensitive to surface potentials.
• Image contrast in MEM is typically attributed to secondary electron trajectories.
• The influence of electric field distortions on MEM image formation requires further investigation.

Purpose of the Study:

• To propose a new interpretation of MEM images based on electric field distortions.
• To investigate the formation of caustics in MEM images due to surface topography and potential variations.
• To demonstrate the utility of MEM image caustics for quantitative surface analysis.

Main Methods:

• Utilizing a ray-based trajectory method to model electron paths.
• Analyzing the overlap of electron rays in the vicinity of the magnetic objective lens imaging plane.
• Employing a through-focus series of MEM images for detailed analysis.

Main Results:

• Electric field distortions can create significant caustics in MEM image contrast.
• These image caustics directly correlate with surface topography and potential variations.
• The contact angle of a Gallium droplet on a GaAs (001) surface was successfully extracted.

Conclusions:

• Image caustics in MEM provide valuable information about surface properties.
• This new interpretation enhances the analytical capabilities of MEM.
• MEM is a powerful tool for quantitative surface characterization and metrology.