Dark-Field Imaging Lens Focus Shift for Aberration Correction
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Solution Overview
Problem
Scanning transmission electron microscopes face challenges in accurately detecting electrons scattered at high angles due to large geometrical aberrations in the objective lens, which affects the quality of dark-field images.
Innovation Solution
The method involves shifting the focus of the imaging lens group from the diffraction plane of the objective lens to reduce geometrical aberration effects, allowing for accurate detection of electrons scattered in a predetermined angular range by the dark-field detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the imaging lens group is focused on the diffraction plane of the objective lens, then the detection system can operate with standard focusing, but electrons scattered at high angles are not accurately detected due to geometrical aberration
Solution Approach 1:
The patent changes the focusing parameter of the imaging lens group by shifting the focus from the diffraction plane to a position behind it. This parameter change compensates for the geometrical aberration caused by the objective lens, enabling accurate detection of electrons scattered at high angles while maintaining a relatively simple focusing operation.
2Ease of manufacture
If the objective lens has large geometrical aberration, then the lens can be used with simpler design, but electrons scattered at high angles are converged stronger and cannot be accurately detected
Solution Approach 1:
The patent converts the harmful effect of geometrical aberration (which causes over-convergence of high-angle scattered electrons) into a beneficial effect by deliberately shifting the focus position. The aberration-induced convergence is compensated by positioning the focus behind the diffraction plane, transforming the manufacturing simplicity advantage into accurate detection capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate detection of electrons scattered at high angles, even when the objective lens has significant geometrical aberration, improving the quality of dark-field images by correcting aberration-induced convergence issues and maintaining detection precision.
Implementation Method 1
an imaging lens group disposed at a stage following the objective lens
Implementation Method 2
detecting electrons scattered at a specimen in a predetermined angular range
Data Source
AI summary
A method of acquiring a dark-field image for a scanning transmission electron microscope is provided. The scanning transmission electron microscope includes a dark-field detector having an annular detection region which is capable of detecting electrons scattered at a specimen in a predetermined angular range, an objective lens, and an imaging lens group disposed at a stage following the objective lens. The method includes reducing an influence of a geometrical aberration on the electrons scattered in the predetermined angular range by shifting a focus of the imaging lens group from a diffraction plane of the objective lens.