Considerations for the quantitative analysis of coated reliefs

Area of Science:

• Materials Science
• Electron Microscopy
• Image Analysis

Background:

• Transmission electron microscopy (TEM) contrast in coated relief specimens is crucial for understanding surface topography.
• Contrast generation depends on the angular relationship between contrast coat evaporation and specimen viewing direction.
• Accurate reconstruction of specimen relief from optical density data requires knowledge of the contrast angle.

Purpose of the Study:

• To elucidate the principles of contrast generation in coated relief specimens for TEM.
• To explore methods for computer-based reconstruction of specimen relief.
• To identify factors influencing the validity of relief reconstruction, such as undercutting and coating techniques.

Main Methods:

• Analysis of contrast formation based on geometrical principles of evaporation and viewing angles.
• Investigation of conditions requiring specimen reorientation using rotate/tilt holders.
• Evaluation of undercutting phenomena and its impact on reconstruction accuracy.
• Exploration of "vertical" coating and bidirectional contrasting techniques.

Main Results:

• Contrast is directly related to the angular difference between evaporation and viewing directions.
• Specimen reorientation may be necessary when a backing coat is present.
• Undercutting can impede accurate relief reconstruction even with correct orientation.
• "Vertical" coating and bidirectional contrasting offer strategies to enhance relief information.

Conclusions:

• Knowledge of contrast angles is essential for computer reconstruction of specimen relief.
• Careful control of coating and viewing angles, alongside techniques like vertical coating, can mitigate undercutting and improve data acquisition.
• Bidirectional contrasting can increase the information capacity of relief coats for detailed topographical analysis.