Electron Beam Aberration Correction via Multipole Tilt
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Solution Overview
Problem
Current spherical aberration correctors in transmission electron microscopes introduce parasitic aberrations, particularly third-order aberration S3 with 2-fold symmetry, which are difficult to correct due to their origin from the fringing term of the quadrupole field, leading to adverse effects from off-axis aberrations.
Innovation Solution
The electron beam system corrects third-order aberration S3 by tilting the center orbit of the electron beam within the second multipole element relative to the optical axis, controlling the fringing term of the quadrupole field to produce a corrective aberration S3' that cancels out the parasitic aberration S3, while keeping the tilt within the multipole element to avoid off-axis effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spherical aberration corrector is introduced to correct spherical aberration in the objective lens, then spherical aberration is corrected, but new parasitic aberrations (including third-order aberration S3) are produced
Solution Approach 1:
The patent converts the harmful parasitic S3 aberration into a beneficial correction by intentionally introducing a controlled tilt of the electron beam within the multipole element. This tilt generates a fringing term in the quadrupole field that produces a corrective S3' aberration to cancel out the parasitic S3, thereby transforming the harmful effect into a useful correction mechanism
Solution Approach 2:
The patent changes the parameter of electron beam trajectory by tilting it relative to the optical axis within the multipole element. This parameter change (tilt angle) directly controls the generation of the fringing term in the quadrupole field, enabling precise adjustment of the corrective S3' aberration to match and cancel the parasitic S3
2Measurement precision
If off-axis aberration is used to correct S3 aberration by causing electron trajectory to pass off the optical axis, then S3 correction is achieved, but many other low-order aberrations are produced outside the axis
Solution Approach 1:
The patent applies local quality by restricting the beam tilt effect to occur only within the multipole element where the fringing term can be effectively generated. By confining the tilt to this specific location rather than using general off-axis trajectories, the correction is localized to where it is needed while avoiding the generation of other aberrations that would occur with extended off-axis paths
3Measurement precision
If the electron beam is tilted within the multipole element to correct S3, then the fringing term of the quadrupole field is controlled to produce corrective aberration, but the system complexity increases
Solution Approach 1:
The patent employs self-service by utilizing the existing multipole element's quadrupole field and its inherent fringing term to generate the corrective aberration. Rather than introducing a separate correction device, the system uses the multipole element itself to produce the necessary S3' correction through controlled beam tilt, making the correction mechanism self-contained within the existing optical components
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 method effectively corrects the third-order aberration S3 with 2-fold symmetry, improving the system's resolution and enabling high-resolution STEM imaging by reducing parasitic aberrations, allowing for a smaller electron beam diameter and precise analysis of microscopic areas.
Implementation Method 1
The aberration S3 originates from the fringing term of the quadrupole field. That is, the aberration S3 depends on the term of the quadrupole field differentiated twice by a parameter Z that is the amount of motion of electrons in the direction of motion.
Implementation Method 2
tilting the center orbit of the electron beam within the second multipole element relative to the optical axis such that the third-order aberration (S3) with 2-fold symmetry is corrected
Data Source
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AI summary
There is disclosed an electron beam system in which the third-order aberration S3 with two-fold symmetry is corrected. If a Cs corrector (17) is operated, parasitic aberration S3 (third-order aberration S3 with two-fold symmetry) is produced. A corrective third-order aberration S3' with two-fold symmetry that cancels out the parasitic aberration S3 is produced within a multipole element (3,7) to correct the parasitic aberration S3. The electron beam (EB) is tilted relative to the optical axis (O) within the multipole element producing a hexapole field. The corrective third-order aberration S3' with two-fold symmetry is introduced in each electron forming the tilted electron beam.