Cs-corrected HAADF-STEM imaging of silicate minerals.

Area of Science:

• Mineral Physics
• Materials Science
• Electron Microscopy

Background:

• Advancements in electron microscopy, particularly spherical aberration correction (Cs-corrector), have significantly enhanced resolution.
• Cs-corrected transmission electron microscope (TEM) and scanning TEM (STEM) achieve resolutions near 1 Angstrom, crucial for atomic-scale analysis.
• Silicate minerals commonly feature cation columns separated by approximately 1.5 Angstroms, resolvable with modern electron microscopy.

Purpose of the Study:

• To investigate local atomic structures in silicate minerals using Cs-corrected STEM.
• To resolve and differentiate cation site occupancies and distributions in specific silicate samples.

Main Methods:

• High-angle annular dark-field (HAADF) imaging with Cs-corrected STEM was employed.
• Advanced noise filtering techniques were utilized to enhance image quality.
• Image contrast was compared with simple simulations to interpret cation distribution.

Main Results:

• All cation columns in orthopyroxene (Opx) were resolved along the c-axis.
• A sub-angstrom positional difference in the M2 site between Opx and augite was detected, correlating with Fe and Ca occupation.
• Unequal contrast in tetrahedral cation columns of cronstedtite suggested differential Fe(3+) substitution.

Conclusions:

• Cs-corrected STEM provides atomic-level insights into cation ordering and substitution in silicates.
• The technique successfully differentiated mineral compositions and revealed cation distribution patterns.
• Fe(3+) distribution in cronstedtite likely avoids adjacent Fe-coordinated tetrahedrons.