Aperture-Limited Segmented Detector for STEM Aberration Measurement
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Solution Overview
Problem
Scanning transmission electron microscopes equipped with segmented detectors face challenges in accurately measuring aberrations due to blurring of STEM images, especially when trying to detect high-order aberrations, as the sectorial detector segments spread the angle of incidence, making it difficult to compute image shifts accurately.
Innovation Solution
The introduction of an aperture that limits the active areas of the detector segments, allowing for improved angular resolution and accurate measurement of aberrations by restricting the active areas on which electrons impinge, thereby reducing blurring and enabling the detection of higher-order aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If sectorial detector segments are used to detect transmitted electrons, then the detector can measure solid angle dependence of electron scattering, but the detector segments spread the angle of incidence causing blurring of STEM images
Solution Approach 1:
The detection surface is divided into multiple detector segments that can be independently controlled. By selectively activating only those segments corresponding to a specific angular range, the system maintains the ability to measure solid angle dependence while reducing angular spread for each measurement, thereby minimizing image blurring.
Solution Approach 2:
Different detector segments are assigned to detect electrons within specific angular ranges. By limiting the active detection area to local segments rather than the entire detection surface, each segment measures a narrower angular range, reducing the spreading effect and improving image sharpness while still enabling comprehensive angular coverage through multiple segments.
2Quantity of substance
If the active area of detector segments is not limited, then more electrons are detected, but angular resolution deteriorates making it difficult to compute image shifts accurately
Solution Approach 1:
Instead of using the entire detection surface simultaneously, the system activates only a partial set of detector segments corresponding to a limited angular range. This partial action approach improves angular resolution by reducing the angular spread, while the quantity of detected electrons is maintained through sequential or selective activation of different segment groups.
3Device complexity
If a small number of detector segments are used, then the device complexity is reduced, but the ability to detect high-order aberrations is limited
Solution Approach 1:
The system dynamically controls the activation and configuration of detector segments based on the specific measurement requirements. By adaptively selecting which segments to activate and how to configure them, the system can achieve high-order aberration detection capability with fewer physical segments, as the same segments can be reconfigured for different measurement modes.
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 solution enhances the accuracy of aberration measurement by reducing image blurring and improving angular resolution, allowing for the detection of aberrations up to higher orders, even with a small number of detector segments.
Implementation Method 1
If there is aberration (geometric aberration), as the angle of convergence α to the sample S increases, the electron beam EB intersects the optical axis 2 more forwardly of the sample S
Implementation Method 2
A segmented detector whose detection surface is divided into plural detector segments is known as an electron detector equipped in such a scanning transmission electron microscope. The segmented detector has independent detection systems for the detector segments, respectively.
Data Source
AI summary
An electron microscope capable of measuring aberrations accurately is provided. The microscope is adapted to obtain scanning transmission electron (STEM) images by detecting electrons transmitted through a sample (S). The microscope (100) includes a segmented detector (20) having a detection surface (23) for detecting the electrons transmitted through the sample (S). The detection surface (23) is divided into detector segments (D1-D16) for detecting the electrons transmitted through the sample (S). The microscope (100) further includes an aperture plate (30) for limiting the active areas of the detector segments (D1-D16) on which the electrons impinge.