Robust Local Thickness Estimation of Sub-Micrometer Specimen by 4D-STEM.

Area of Science:

• Materials Science
• Electron Microscopy
• Nanotechnology

Background:

• Accurate thickness measurement of amorphous specimens is critical for transmission electron microscopy (TEM) analysis, particularly for focused ion beam (FIB)-milled lamellae.
• Existing methods may require signal intensity calibration or are not suitable for in situ monitoring.

Purpose of the Study:

• To present a quantitative four-dimensional scanning transmission electron microscopy (4D-STEM) imaging technique (q4STEM) for local thickness estimation.
• To demonstrate the robustness and applicability of the q4STEM method for amorphous specimens.

Main Methods:

• Utilized spatially resolved diffraction patterns to measure electron scattering angular distribution.
• Quantitatively evaluated scattering data using Monte Carlo simulations.
• Employed ratio of integrated virtual dark and bright field STEM signals.

Main Results:

• The q4STEM method provides robust thickness estimates for sub-micrometer amorphous specimens.
• The technique is independent of signal intensity calibrations, requiring only detector geometry knowledge.
• Successful application demonstrated with both direct detection and light conversion 2D-STEM detectors.

Conclusions:

• The q4STEM technique offers a facile and low-dose method for thickness estimation in amorphous materials.
• Anticipated applications include in situ thickness monitoring during lamella fabrication for beam-sensitive materials.
• This method enhances the reliability of TEM analysis for FIB-prepared samples.