STEM Objective Lens Asymmetric Pole Piece Gap
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Solution Overview
Problem
Scanning transmission electron microscopes (STEMs) face limitations in reducing lens aberration, particularly spherical aberration, which affects high-resolution performance and sample tilt, and existing solutions complicate detector arrangements leading to reduced scan fields and out-of-focus diffraction patterns.
Innovation Solution
The STEM design features an objective electromagnetic lens with a pole piece gap configuration allowing diffraction patterns to form outside the gap, enabling an asymmetrical sample placement for improved aberration minimization and increased detection efficiency with multiple EDS detectors and an ultra-high angle annular dark field detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the pole piece gap is reduced to minimize spherical aberration, then lens aberration is reduced, but the mechanical stability and sample tilt capability deteriorate
Solution Approach 1:
The patent applies asymmetry by placing the sample asymmetrically within the pole piece gap, specifically at a distance of 0.5-2 mm from the lower pole piece face. This asymmetric positioning allows the system to achieve optimal aberration correction while maintaining sufficient mechanical stability and sample tilt capability that would be compromised in a symmetric configuration.
2Productivity
If detectors are placed closer to the sample to increase detection efficiency, then detection efficiency improves, but the risk of detector damage from direct beam exposure increases
Solution Approach 1:
The patent uses the asymmetric sample positioning as an intermediary mechanism that enables detectors to be placed closer to the sample (within 10 mm) while protecting them from direct beam exposure. The sample itself acts as a mediator that allows the detectors to benefit from proximity-enhanced detection efficiency while the asymmetric geometry prevents direct beam damage.
3Manufacturing precision
If the pole piece gap is reduced to improve resolution, then high-resolution performance improves, but the maximum sample tilt and detection efficiency are limited
Solution Approach 1:
The asymmetric sample positioning (0.5-2 mm from lower pole piece face) enables the system to achieve reduced spherical aberration for high-resolution performance while simultaneously providing sufficient space for sample tilt adjustments and detector placement, thereby maintaining adaptability and versatility.
4Adaptability or versatility
If de-scanning coils are used for higher scan fields, then scan field capability improves, but the use is limited by the objective lens configuration
Solution Approach 1:
The asymmetric sample positioning configuration serves multiple functions: it optimizes aberration correction, enables flexible detector placement, and provides adequate space for de-scanning coil arrangements. This multi-functional design allows the system to achieve higher scan field capabilities without proportionally increasing device complexity.
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 configuration enhances high-resolution performance at low energies, allows larger detectors closer to the sample, and doubles X-ray detection efficiency, while maintaining flexibility in scan fields and diffraction pattern applications.
Implementation Method 1
an objective electromagnetic lens with a pole piece gap configuration allowing diffraction patterns to form outside the gap
Implementation Method 2
X-ray radiation resulting from the interaction of the primary beam of electrons with the atoms of the sample can be collected and analysed to determine the elemental composition of the sample
Implementation Method 3
The transmitted electrons are focused by the objective imaging lens(es) according to their scattering angle in a diffraction pattern (BF/DF) located in the back focal plane of the objective lens
Data Source
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AI summary
The object of the present invention provides a scanning transmission electron microscope with the ability to forme at least one diffraction pattern. The scanning electron microscope comprises an electron source, which is configured to provide primary electron beam, a condenser lens system, an objective electromagnetic system, a projection lens system and a detection system. In addition, the objective electromagnetic lens consists of an upper pole piece and a lower pole piece, wherein each pole piece comprises a pole piece face, which is a flat surface oriented towards a sample plane. A salient feature of the present invention is to form at least one diffraction pattern located in the distance from the lower pole piece face outside the pole piece gap, wherein the pole piece gap is the space between the upper pole piece face and the lower pole piece face.