TEM Phase Plate Orbital Motion Suppresses Ringing Artifacts
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Solution Overview
Problem
Transmission Electron Microscopes (TEMs) face challenges in achieving high contrast at low spatial frequencies due to the abrupt edge of phase plates causing 'ringing' artifacts and sensitivity to small irregularities, which affects image quality, especially in biological samples with low-Z materials.
Innovation Solution
The contrast enhancing device, such as a phase plate, is moved in an orbital mode relative to the beam of unscattered electrons, creating a gradual transition in the Fourier domain to suppress ringing and reduce the impact of small irregularities, allowing for improved contrast enhancement without the need for a very small central hole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a phase plate with an abrupt edge is used to improve contrast at low spatial frequencies, then contrast enhancement is achieved, but ringing artifacts are introduced
Solution Approach 1:
The phase plate is made movable relative to the electron beam, transitioning from a static to a dynamic configuration. The phase plate moves in an orbital or circular path around the beam center, creating a time-averaged gradual transition instead of an abrupt edge, thereby suppressing ringing artifacts while maintaining contrast enhancement
Solution Approach 2:
The phase plate performs periodic orbital motion around the beam center at a frequency higher than the frame rate of image acquisition. This periodic movement creates a time-averaged effect where the abrupt edge is distributed around the beam, resulting in a gradual transition that reduces ringing while preserving the phase shift function
2Illumination intensity
If a very small central hole is used in the phase plate to improve contrast, then contrast enhancement is achieved, but the phase plate becomes sensitive to small irregularities and harder to manufacture
Solution Approach 1:
The movable phase plate allows the use of a larger central hole diameter since the orbital motion distributes the phase shift effect across a wider area over time. This dynamic approach reduces sensitivity to small irregularities and simplifies manufacturing while maintaining effective contrast enhancement at low spatial frequencies
Solution Approach 2:
The phase plate is pre-positioned to orbit around the beam center rather than requiring precise static centering. This preliminary orbital configuration allows for easier alignment and manufacturing since the time-averaged effect compensates for small deviations in hole diameter and position, reducing sensitivity to manufacturing tolerances
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 significantly reduces 'ringing' artifacts and enhances contrast at low spatial frequencies, improving image quality and ease of manufacturing while maintaining high electron transparency and phase shift effectiveness.
Implementation Method 1
In this plane it is possible to introduce, for example, a phase shift of −π/2 to all electrons except the unscattered beam
Implementation Method 2
the diffracted and unscattered electrons interfere with each other to form an image
Implementation Method 3
The back-focal plane of the objective lens is a Fourier representation of the image
Data Source
AI summary
The invention relates to a method of forming an image of a sample in a transmission electron microscope equipped with a phase plate. Prior art use of such a phase plate can introduce artifacts in the form of ringing and a halo. These artifacts are caused by the abrupt changes in the Fourier domain due to the sharp edges of the phase plate in the diffraction plane. By moving the phase plate with respect to the non-diffraction beam (the diffraction pattern) while recording an image the sudden transition in the Fourier domain is changed to a more gradual transition, resulting in less artifacts.