Voxel dose-limited resolution for thick beam-sensitive specimens imaged in a TEM or STEM

Area of Science:

• Microscopy
• Materials Science
• Biophysics

Background:

• Radiation damage is a primary limitation in high-resolution imaging of thick specimens.
• Understanding the dose-limited resolution (DLR) is crucial for optimizing imaging parameters.
• Existing models often do not fully account for radiation effects in thick organic samples.

Purpose of the Study:

• To quantify the resolution limit imposed by radiation damage in thick specimens.
• To derive an analytical formula for voxel dose-limited resolution (DLR).
• To evaluate the impact of electron energy and heavy-metal staining on DLR.

Main Methods:

• Derivation of an analytical formula for voxel dose-limited resolution (DLR).
• Application of the DLR formula to bright-field mass-thickness contrast imaging.
• Analysis of organic specimens (polymers, biological) with thicknesses from 400 nm to 20 µm.
• Consideration of electron energies from 300 keV to 3 MeV and heavy-metal staining.

Main Results:

• Radiation damage, not lens aberrations, dictates TEM/STEM resolution for thick organic specimens at typical doses (330 MGy).
• Increasing electron energy (300 keV to 3 MeV) improves DLR by up to a factor of 2.
• Heavy-metal staining enhances DLR by up to a factor of 3.
• Voxel DLR improvement from increased electron dose is modest (proportional to the 1/4 power of dose).

Conclusions:

• Voxel DLR provides a critical metric for assessing imaging resolution limits due to radiation damage in thick samples.
• Optimizing electron energy and employing heavy-metal staining are effective strategies to mitigate radiation damage effects.
• The derived DLR formula is applicable to various thick organic specimens in TEM and STEM.