Cryogenic EBSD on ice: preserving a stable surface in a low pressure SEM

Area of Science:

• Glaciology
• Materials Science
• Crystallography

Background:

• Naturally deformed ice exhibits subgrains with distinct geometries.
• High-resolution light microscopy (LM) has identified these features on etched ice surfaces.
• Electron backscattered diffraction (EBSD) can determine slip systems but requires stable ice surfaces.

Purpose of the Study:

• To develop a method for acquiring EBSD data on stable ice surfaces in a low-pressure scanning electron microscope (SEM).
• To retain etched surface features for correlating with EBSD microstructural data.
• To analyze subgrain boundary types in naturally deformed ice.

Main Methods:

• Operating a low-pressure SEM at temperatures below -112°C to minimize ice sublimation.
• Utilizing beam defocusing to reduce charging artifacts at low pressures.
• Acquiring EBSD data and correlating it with LM-imaged etch features.

Main Results:

• A method was established for collecting EBSD data on stable ice surfaces, preserving etch features.
• Sublimation was significantly reduced at temperatures <-112°C.
• Excellent agreement was achieved between LM etch features and EBSD mapped microstructures.
• Identified subgrain boundary types include basal (tilt and twist) and nonbasal dislocations (tilt boundaries).

Conclusions:

• The developed method allows for detailed microstructural analysis of deformed ice using EBSD.
• Preservation of surface etch features is crucial for understanding ice deformation mechanisms.
• The findings provide insights into the types of dislocations present in naturally deformed ice.