Electron Microscope Angular Aperture Stop Adjustment
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Solution Overview
Problem
Conventional scanning transmission electron microscopes face difficulties in adjusting the angular aperture of the electron beam during high magnification imaging, requiring cumbersome adjustments of lens strengths and aberration correction conditions, which complicates the adjustment process and extends observation time.
Innovation Solution
An electron microscope design featuring a spherical aberration corrector, a transfer lens system between the corrector and the objective lens, and an angular aperture stop movably positioned near the transfer lens system, allowing fine adjustments to the angular aperture without modifying the aperture stop's hole diameters, thereby simplifying aberration correction during high-magnification imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If aperture stops with greatly different hole diameters are used to adjust angular aperture, then the device structure is simplified, but the adjustment precision of angular aperture deteriorates
Solution Approach 1:
The aperture stop system is divided into two independent parts: a fixed aperture stop with a specific hole diameter and a movable angular aperture stop with a smaller hole. This segmentation allows each component to perform its specific function - the fixed aperture stop determines the beam diameter while the angular aperture stop precisely controls the angular aperture, thereby achieving fine adjustment capability without complicating the overall structure.
Solution Approach 2:
The angular aperture stop acts as an intermediary element between the fixed aperture stop and the objective lens. By positioning this intermediate aperture stop at a specific location in the optical path, it enables precise control of the angular aperture independent of the fixed aperture stop's hole diameter, thus resolving the contradiction between structural simplicity and adjustment precision.
2Ease of operation
If the angular aperture is adjusted by varying lens strength, then the adjustment mechanism is simplified, but the aberration correction conditions must be readjusted which increases system complexity
Solution Approach 1:
The control of angular aperture is separated from the lens strength adjustment. Instead of varying lens strength, the angular aperture is independently controlled by moving the angular aperture stop laterally. This segmentation allows angular aperture adjustment without affecting aberration correction conditions, maintaining system stability while improving ease of operation.
Solution Approach 2:
The function of angular aperture control is extracted from the lens strength adjustment mechanism and assigned to a dedicated angular aperture stop. This extracted function can be adjusted independently by lateral movement of the stop, eliminating the need to readjust aberration correction conditions when changing angular aperture, thus reducing system complexity.
3Ease of operation
If aperture stops are positioned close to the condenser lens principal plane, then the current control is effective, but the total current impinging on the specimen does not vary when condenser lens strength is changed
Solution Approach 1:
The angular aperture stop serves as an intermediary element that enables current variation when the condenser lens strength is changed. By positioning this stop at a specific location, it mediates between the condenser lens and the specimen, allowing the total current to be varied through lateral movement of the stop while maintaining effective emission current control.
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 design enables easy correction of aberrations during high-magnification imaging by allowing precise adjustment of the angular aperture, reducing the time required for adjustments and suppressing residual aberrations, thus enhancing imaging resolution and efficiency.
Implementation Method 1
the spherical aberration corrector produces a negative spherical aberration that cancels out the positive spherical aberration of the objective lens
Implementation Method 2
two transfer lens subassemblies giving a magnification M of 1 or more are disposed between a spherical aberration corrector and an objective lens
Implementation Method 3
an angular aperture stop mounted at or near the principal plane of the transfer lens system movably relative to the optical axis to adjust the angular aperture of the electron beam
Data Source
AI summary
An electron microscope is offered which facilitates aberration correction even during high-magnification imaging. The microscope has a spherical aberration corrector, a transfer lens system mounted between the corrector and an objective lens, an aperture stop mounted in a stage preceding the corrector so as to be movable relative to the optical axis, and an angular aperture stop mounted at or near the principal plane of the transfer lens system movably relative to the optical axis to adjust the angular aperture of the electron beam.