TEM Illumination Control for Constant Beam Convergence
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Solution Overview
Problem
In transmission electron microscopes, changing the illuminating area of the electron beam using the illumination system lens alters the convergence angle, making it difficult to accurately acquire bright-field and dark-field images.
Innovation Solution
A configuration with a first and second illumination system lens, deflectors, and a control unit that adjusts the excitation amounts and control amounts of these components to maintain constant convergence, illuminating position, and angle of the electron beam, even when the illuminating area changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the illuminating area of the electron beam is changed using the illumination system lens, then the illuminating area is adjusted, but the convergence angle changes causing inaccurate bright-field and dark-field images
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting multiple parameters (excitation amounts of first and second illumination system lenses, and control amounts of first and second deflectors) in a coordinated manner. When the illuminating area needs to be changed, the system modifies the excitation amount of the first illumination system lens, then compensates by adjusting the excitation amount of the second illumination system lens and the control amounts of the deflectors to maintain constant convergence angle, illuminating position, and illuminating angle, thereby preserving image accuracy while changing the illuminating area
Solution Approach 2:
The patent implements feedback control where the control unit continuously monitors the state of the illumination system and automatically adjusts the excitation amounts and control amounts to maintain optimal optical conditions. The system uses the relationship between the excitation amount of the first illumination system lens and the required compensation values for the second illumination system lens and deflectors to ensure that the convergence angle, illuminating position, and illuminating angle remain constant despite changes in illuminating area
2Area of moving object
If the excitation amount of the first illumination system lens is changed to adjust illuminating area, then the illuminating area is modified, but the illuminating position and angle change requiring additional control components
Solution Approach 1:
The patent segments the illumination system into two independent controllable parts: the first illumination system lens for controlling illuminating area, and the second illumination system lens combined with deflectors for maintaining optical parameters. This segmentation allows each component to have a specialized function, reducing the overall complexity by distributing the control functions across multiple simpler components rather than requiring a single complex lens system
Solution Approach 2:
The patent introduces deflectors as intermediary components between the first and second illumination system lenses. These deflectors act as mediators that can adjust the electron beam path to compensate for changes in illuminating position and angle caused by modifying the first illumination system lens excitation. The deflectors provide a simple mechanical means of correction without requiring complex lens redesign
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
Ensures consistent acquisition of bright-field and dark-field images by maintaining the convergence angle, illuminating position, and angle of the electron beam, regardless of changes in the illuminating area, thereby improving image quality and allowing continuous observation of specimens with high contrast.
Implementation Method 1
an electron beam emitted from an electron gun is focused by an illumination system lens
Implementation Method 2
the electron beam transmitted through the specimen forms a crossover on a back focal plane of the objective lens
Implementation Method 3
a first deflector and a second deflector that are disposed between the first illumination system lens and the second illumination system lens
Data Source
AI summary
A transmission electron microscope includes a control unit that: determines an excitation amount of a second illumination system lens based on an excitation amount of first illumination system lens such that the second illumination system lens satisfies a first optical condition; and determines a control amount of a first deflector and a control amount of a second deflector based on the excitation amount of the second illumination system lens such that the first deflector and the second deflector satisfy a second optical condition. The first optical condition is for a convergence angle of the electron beam to be constant even if the excitation amount of the first illumination system lens has changed, and the second optical condition is for an illuminating position of the electron beam and an illuminating angle of the electron beam to be constant even if the excitation amount of the first illumination system lens has changed.