TEM Blocking Member for Low Frequency Contrast
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Solution Overview
Problem
Current Transmission Electron Microscope (TEM) imaging techniques, such as single-sideband imaging, suffer from limited contrast at low spatial frequencies, making it difficult to detect large structures in biological samples, and existing solutions like phase plates require additional electrical voltages or fragile carbon films.
Innovation Solution
A blocking member is positioned in the diffraction plane to selectively block high spatial frequencies, allowing more than 50% of the envelope function contrast, without discarding half of the electrons, thereby enhancing contrast at low frequencies and maintaining high resolution by using a heavy metal blocking member that does not require additional electrical voltages or fragile films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If single-sideband imaging is used to block half of the diffraction plane, then contrast at low spatial frequencies is improved, but more than 50% of electrons are discarded and resolution is limited
Solution Approach 1:
The patent applies local quality by implementing an annular blocking member that selectively blocks only the outer region of the diffraction plane corresponding to high spatial frequencies, while leaving the central region (low spatial frequencies) open. This localized blocking approach improves contrast at low frequencies without discarding all high-frequency information, thereby maintaining better resolution compared to single-sideband imaging that blocks half the entire diffraction plane.
2Illumination intensity
If phase plates are used to improve low frequency contrast, then additional electrical voltages or fragile carbon films are required, but this increases device complexity and reliability issues
Solution Approach 1:
The patent extracts the problematic components (phase plates requiring electrical voltages or fragile carbon films) by replacing them with a simple annular blocking member made of heavy metal. This blocking member physically removes only the unwanted high spatial frequency components from the diffraction plane, achieving contrast enhancement without the complexity and reliability issues of phase plates.
3Illumination intensity
If a blocking member blocks high spatial frequencies, then contrast at low frequencies is enhanced, but resolution may be compromised
Solution Approach 1:
The patent applies partial action by using an annular blocking member that blocks only the outer region of the diffraction plane (high spatial frequencies) while leaving the central region (low spatial frequencies) completely open. This partial blocking strategy enhances contrast at low frequencies without completely eliminating high-frequency information, thereby maintaining better resolution compared to methods that block larger portions of the diffraction plane.
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
The solution achieves improved contrast at low spatial frequencies while maintaining high resolution, outperforming single-sideband imaging by providing more than 50% of the envelope function contrast across a large frequency band, without the limitations of existing phase plate technologies.
Implementation Method 1
Some electrons are elastically scattered by the sample, and leave the sample under another direction than that they entered the sample. These scattered electrons are focused by the objective lens and form in the back-focal plane, of said objective lens, also known as the diffraction plane, a diffraction pattern.
Implementation Method 2
the pattern formed in the diffraction plane represents the (Fourier) transform of the image plane to the Fourier plane
Implementation Method 3
using a heavy metal blocking member that does not require additional electrical voltages or fragile films
Data Source
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AI summary
The invention relates to a blocking member to be placed in the diffraction plane of a TEM. It resembles the knife edge used for single sideband imaging, but blocks only electrons deflected over a small angle. As a result the Contrast Transfer Function of the TEM according to this invention will equal that of a single sideband microscope at low frequencies and that of a normal microscope for high frequencies. Preferable the highest frequency blocked by the blocking member is such that a microscope without the blocking member would show a CTF of 0.5.