Hexapole Corrector for Spherical Aberration and Coma
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Solution Overview
Problem
High-resolution electron microscopy is limited by third-order spherical aberration and off-axis coma, which restricts image size and quality, with existing correctives either leaving anisotropic coma uncorrected or being overly complex and inflexible.
Innovation Solution
The use of strategically arranged hexapole fields with varying strengths and orientations, along with round lenses, to eliminate third-order spherical aberration and both isotropic and anisotropic off-axis coma, allowing for adjustable correction power and simplified implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three or more strong hexapole fields are used, then both spherical aberration and off-axis coma are corrected, but the system becomes overly complex and inflexible
Solution Approach 1:
Different regions of the corrective have different field strengths and orientations optimized for their specific correction tasks. The outer hexapole fields have stronger strength for spherical aberration, while inner hexapole fields have adjusted strength and orientation for off-axis coma, allowing efficient correction with reduced overall complexity.
Solution Approach 2:
The corrective includes adjustable magnification between the objective lens and corrective, allowing the correction power to be electrically adjusted. This dynamic capability provides flexibility without requiring multiple fixed correction systems, reducing complexity while maintaining adaptability.
2Adaptability or versatility
If the intermediate magnification is adjusted, then the correction power is adapted, but the optical quality deteriorates in existing systems
Solution Approach 1:
The corrective design allows intermediate magnification to be adjusted to adapt correction power to the spherical aberration of the objective lens. The multi-field structure maintains optical quality across different magnification settings by distributing correction functions across multiple fields that work together synergistically.
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 the simultaneous correction of third-order spherical aberration and off-axis coma, significantly enlarging the sharply imaged image area and providing flexibility in adjusting the correction power without compromising optical quality.
Implementation Method 1
The corrective contains hexapole fields, between which round lenses are introduced. The strength ratios of the hexapole fields are selected in such a way that the image aberration coefficients of the axial threefold astigmatism of the 2nd order become 0.
Implementation Method 2
round lenses and hexapole fields. The strengths of the round lens fields and the hexapole fields are symmetrical to the center plane.
Data Source
Figure 1
AI summary
Disclosed is a particle-optical corrector for eliminating third-order spherical aberration and third-order coma with the aid of round lenses and hexapole fields. Said corrector is composed of three coaxially arranged hexapole fields. One respective round lens doublet is disposed between adjacent hexapole fields and is adjusted such that the central hexapole field is reproduced onto the hexapole fields while an intermediate plane comes to lie between the hexapole fields, the intermediate planes being conjugate and the three hexapole fields being oriented the same way in the Larmor reference system. Furthermore, the intensities of the three fields are selected such that the threefold astigmatism coefficient amounts to 0. The inventive corrector comprises two couples of hexapole fields in which the fields of each couple of hexapole fields are excited asymmetrically relative to one another while the respective couples are placed around the two intermediate planes. The alignment of the couples of hexapole fields is rotated by such an angle relative to the alignment defined by the hexapole fields that the third-order coma is corrected.