Local sample thickness determination via scanning transmission electron microscopy defocus series

Area of Science:

• Materials Science
• Nanotechnology
• Electron Microscopy

Background:

• Aberration correction has increased usable aperture sizes in scanning transmission electron microscopy (STEM).
• Increased convergence angles have reduced depth of focus, enabling optical sectioning in STEM.
• Accurate sample thickness measurement is crucial for transmission electron microscopy (TEM) analysis.

Purpose of the Study:

• To develop and validate a method for determining local sample thickness using STEM defocus series.
• To leverage optical sectioning capabilities of STEM for quantitative thickness measurements.
• To provide a high-resolution, simulation-free approach for TEM sample thickness determination.

Main Methods:

• Acquisition of experimental and simulated STEM defocus series of thin silicon (Si) foils.
• Quantification of image blurring in high-resolution, high-angle annular dark-field (HAADF) images by analyzing intensity standard deviation.
• Analysis of the relationship between defocus and image blurring to determine sample thickness.

Main Results:

• Image blurring systematically increases with defocus, showing a maximum at optimal defocus.
• The full width half maximum (FWHM) of the defocus-blurring curve correlates directly with sample thickness.
• Thickness measurements from the proposed method show good agreement with established techniques.
• The method is effective for thicknesses above a minimum determined by aperture size and chromatic aberration.

Conclusions:

• STEM defocus series provide a robust method for local sample thickness measurement in TEM.
• The technique offers high spatial resolution and avoids the need for complex simulations.
• This approach enhances quantitative analysis capabilities in electron microscopy.