Phase-contrast electron microscope with diffractive lens magnification
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Solution Overview
Problem
Conventional phase contrast electron microscopes face challenges due to the small dimensions required for phase-shifting elements, leading to contamination, charging issues, and material absorption, which result in low contrast and information loss, making them unsuitable for commercial production.
Innovation Solution
A phase contrast electron microscope design that includes a first diffractive lens imaging the objective's back focal plane into a diffraction intermediate image plane, where a phase-shifting element is placed, allowing for a geometrically enlarged phase-shifting element and reduced dimensional requirements, while minimizing electron masking and aberration effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a phase plate is introduced in the rear focal plane of the objective to generate phase contrast, then contrast gain is improved, but the small diameter of the zero beam (less than 1 μm) creates technological problems including contamination, charging, and dielectric strength issues
Solution Approach 1:
The patent introduces an intermediate magnification stage between the objective and the phase plate, effectively adding a dimensional transformation to the optical path. The first diffractive lens creates an intermediate image plane where the zero beam is magnified before reaching the phase plate, allowing the phase plate to have a larger diameter while still selectively affecting only the zero beam. This resolves the contradiction by changing the spatial dimension at which the phase plate operates.
2Loss of information
If a small electrostatic lens is used as the phase plate to phase-shift only the zero beam, then phase contrast is achieved, but external support structures interrupt the paths of diffracted electrons into higher orders, causing information loss
Solution Approach 1:
The patent introduces an intermediate magnification system consisting of a first diffractive lens and an intermediate image plane as a mediator between the objective and the phase plate. This intermediary stage magnifies the zero beam before it reaches the phase plate, allowing the phase plate to be larger without blocking diffracted beams. The intermediary system resolves the contradiction by providing a spatial buffer that separates the phase-shifting function from the electron path obstruction problem.
3Loss of information
If a thin film is used as the phase plate to phase-shift scattered and null beams, then phase contrast is generated, but the material absorption weakens the already weak higher orders of diffraction
Solution Approach 1:
The patent implements local quality by creating a spatially differentiated phase-shifting mechanism. The magnified intermediate image plane allows the phase plate to selectively affect only the magnified zero beam region while leaving the diffracted higher orders unaffected. This localizes the phase-shifting action to specific spatial coordinates, resolving the contradiction by ensuring that material absorption only impacts the intended zero beam while preserving the integrity of higher diffraction orders.
4Area of stationary object
If the diffraction plane is enlarged and imaged in a diffraction intermediate image plane, then the phase-shifting element can be geometrically enlarged, but the overall length of the system increases
Solution Approach 1:
The patent employs dynamic focusing capabilities through the diffractive lenses, allowing the system to adaptively adjust the magnification and positioning of the intermediate image plane. This dynamic control enables optimization of the balance between phase plate size and system length, resolving the contradiction by providing flexible adjustment rather than fixed geometric constraints.
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 reduces the dimensional demands on phase-shifting elements, minimizes information loss, and maintains high resolution by ensuring the phase-shifting element can be larger, thus enhancing contrast and image quality without deteriorating resolution.
Implementation Method 1
a first diffractive lens which images the back focal plane of the objective magnified into a diffraction intermediate image plane
Implementation Method 2
the phase-shifting element is placed in or near the diffraction intermediate image plane
Data Source
AI summary
The present invention relates to a phase-contrast electron microscope comprising an objective (8) with a rear focal plane (10), a first diffraction lens (11) that magnifies the rear focal plane (10) of the objective (8) and projects it into an intermediate diffraction image plane, a second diffraction lens (215) whose principal plane is located near the intermediate diffraction image plane, and a phase-shifting element (16) located in or near the intermediate diffraction image plane. The invention further relates to a phase-contrast electron microscope comprising an objective (8) with a rear focal plane (10), a first diffraction lens (11) that magnifies the rear focal plane of the objective and projects it into an intermediate diffraction image plane, a first phase-shifting element located in the rear focal plane (10) of the objective (8), and a second phase-shifting element located in or near the intermediate diffraction image plane.The enlarged imaging of the diffraction plane using diffraction lenses reduces the dimensional requirements for the phase plate with the phase-shifting element.