Electron Microscope Aperture Diaphragm Positioning
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Solution Overview
Problem
The design of projection imaging type electron microscopes is restricted by the conditions of the projection electron optical system, particularly due to the placement of aperture diaphragms which can knock out the illuminating beam and cause contamination and aberrations, limiting the degree of freedom in the illumination electron optical system.
Innovation Solution
The aperture diaphragm is positioned at the second electron beam crossover, and a diaphragm is placed at the first crossover to prevent beam knocking and contamination, with a stigmator correcting astigmatic aberrations and a relay optical system optimizing the second crossover position, allowing for increased design freedom in the illumination system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an aperture diaphragm is placed at the first crossover position in the projection electron optical system, then the opening angle of the projection electron optical system can be determined, but the illuminating beam may be knocked out by the aperture diaphragm, causing design restrictions on the illumination electron optical system
Solution Approach 1:
The patent moves the aperture diaphragm from the first crossover position to the second crossover position along the optical axis (a different spatial dimension/position), thereby resolving the conflict between opening angle control and illumination beam interference. This positional relocation allows the aperture diaphragm to fulfill its function of determining the opening angle without blocking or knocking out the illuminating beam, thus restoring design freedom to the illumination electron optical system.
2Manufacturing precision
If the aperture diaphragm opening is made small to control the projection system, then manufacturing precision is improved, but beam contamination and aberrations increase
Solution Approach 1:
The patent introduces a relay optical system as an intermediary between the objective electron optical system and the image focusing electron optical system. This relay optical system includes a relay objective lens and a relay condenser lens that create an intermediate image plane, allowing the aperture diaphragm to be positioned at the second crossover where it can control the projection system without directly interfering with the illuminating beam path, thereby reducing beam contamination and aberrations while maintaining manufacturing precision.
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 alleviates design restrictions, enhances the degree of freedom in the illumination electron optical system, prevents beam contamination, and improves image focusing characteristics by correcting aberrations and maintaining telecentric properties.
Implementation Method 1
the optical path of the illuminating beam 34 is altered by the electromagnetic prism (E×B) 33
Implementation Method 2
the illuminating beam 34 passes through an objective electron optical system 37, and illuminates the surface of a sample 36
Implementation Method 3
these electrons are acted upon by the lenses 39a, 39b, 39c and 39d, and are focused as an image on the MCP detector
Data Source
AI summary
It is an object of the present invention to provide an projection imaging type electron microscope in which the imposition of restrictions on the design of the illumination electron optical system by the conditions of the projection electron optical system is alleviated, so that the degree of freedom in the design of the illumination electron optical system is increased. Generated electrons 6b (principal rays) emitted from the sample 5 parallel to the optical axis are focused by a cathode lens so that these electrons cross the optical axis 3 at one point. This point is the first crossover. The generated electrons 6b are oriented parallel to the optical axis by the cathode lens 4a, and are focused as an image at the position of the electromagnetic prism 2; these electrons pass through the stigmator 7, and are incident on the relay lens 8a. These electrons are again focused, and cross the optical axis 3 at one point. This position is the second crossover. An aperture diaphragm 11 is disposed in this second crossover position. As a result, the need to install an aperture diaphragm in the first crossover position is eliminated, so that design of the illumination electron optical system is facilitated.