Interferometric Electron Microscope With Grating-Biprism Wave Control
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Solution Overview
Problem
Interferometric electron microscopes face limitations in measurement sensitivity due to coherence length constraints, contamination and damage from electron beams on crystals, non-uniform diffracted wave intensity, difficulty in achieving ideal one-dimensional diffraction, and lack of observational freedom in crystal-based systems.
Innovation Solution
An interferometric electron microscope design using an artificial grating with a two-dimensional structure, an electron beam biprism for controlling wave positions, and adjustable electric current densities, allowing for increased coherence length and flexible control over the distance between object and reference waves, thereby enhancing measurement sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the coherence length of the electron wave is increased by using a light source of high luminance or lowering an irradiating electric current density, then the measurement sensitivity is improved, but the luminance of light sources is subject to physical limitations because electrons tend to diverge due to repulsive forces therebetween
Solution Approach 1:
The invention divides the electron beam into multiple partial beams using a diffraction grating, where each partial beam can be independently controlled and focused. This segmentation allows the system to achieve high measurement sensitivity through interference of multiple coherent beams without requiring a single high-luminance source, thereby overcoming the electron divergence limitation.
Solution Approach 2:
The patent implements a nested structure where the diffraction grating is positioned within the electron optical system, and multiple partial beams are nested within the overall beam path. Each partial beam undergoes independent optical processing while contributing to the final interference pattern, enabling high sensitivity measurements without exceeding source luminance limits.
2Measurement precision
If an artificial grating is used to produce diffracted waves, then the coherence length is increased and various electron sources can be used, but the irradiated area of the crystal tends to be contaminated and damaged by the electron beam
Solution Approach 1:
The invention uses an artificial grating structure that can be precisely replicated and positioned without being directly in the path of the high-intensity electron beam. The grating pattern is copied onto a support structure that redirects the beam, allowing the crystal or specimen to be measured without direct beam exposure that would cause contamination or damage.
Solution Approach 2:
The artificial grating acts as an intermediary element that modulates the electron beam without requiring the specimen or crystal to be directly irradiated. The grating structure diffracts the beam into partial waves that then interact with the specimen, separating the function of beam modulation from beam delivery and reducing harmful direct irradiation.
3Measurement precision
If a crystal is used to produce diffracted waves, then interference can be achieved, but the intensity of the diffracted wave is not uniform, failing to make highly accurate measurements
Solution Approach 1:
The patent employs an artificial grating with locally optimized structures where each region of the grating is designed to produce uniform diffraction efficiency. The grating lines are precisely engineered with controlled depth, width, and spacing to ensure uniform intensity distribution across all diffracted orders, unlike natural crystals which have inherent variations.
Solution Approach 2:
The invention changes the physical parameters of the diffraction structure from natural crystal lattice parameters to engineered artificial grating parameters. By controlling the grating period, depth, and profile during fabrication, the system achieves uniform diffraction intensity that can be precisely tuned, overcoming the non-uniformity inherent in crystal-based diffraction.
4Measurement precision
If a crystal is irradiated by an electron beam having a diameter of several nm, then diffraction can be achieved, but the irradiated area of the crystal tends to be contaminated and damaged by the electron beam
Solution Approach 1:
The invention extracts the diffraction function from the crystal or specimen by using a separate artificial grating element. This allows the high-precision diffraction to occur in the grating while the specimen remains undamaged and can be measured repeatedly over time without contamination or degradation from direct beam exposure.
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 increases measurement sensitivity per unit time, improves time resolution, and enables highly accurate phase analysis with high-magnification, high-contrast holograms, while avoiding beam-induced contamination and irregularities, and providing greater observational flexibility.
Implementation Method 1
an artificial grating 13 is irradiated by an electron wave 2
Implementation Method 2
electron waves 7 and 8 are superimposed on each other on an observation plane 11 where they interfere with each other, producing interference fringes
Implementation Method 3
The electron wave 2 has its electric current density adjusted by a first irradiating electron lens 3 and a second irradiating electron lens 4
Data Source
Figure 1
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Figure 3
AI summary
An interferometric electron microscope is capable of increasing an irradiating electric current density, is free of problems caused by using a crystal, and is able to freely control the distance between an object wave and a reference wave on a specimen plane. The interferometric electron microscope causing electron waves to interfere with each other includes: an electron source (1); an irradiating lens system (3, 4) irradiating a specimen with an electron beam emitted from the electron source (1); a focusing lens system (5, 9) focusing an image of the specimen; an observational plane (11) used for observing the image of the specimen focused by the focusing lens system (5, 9); an artificial grating (13) disposed between the electron source (1) and the irradiating lens system (3, 4) and diffracting the electron beam emitted from the electron source (1) to produce a first electron wave and a second electron wave; an electron beam biprism (14) in an irradiating system disposed in the irradiating lens system (3, 4) and deflecting the first electron wave and the second electron wave to pass the first electron wave through the specimen for use as an object wave and to use the second electron wave as a reference wave; and an electron beam biprism (10) in a focusing system disposed in the focusing lens system (5, 9) and deflecting the objective wave and the reference wave to superimpose the objective wave and the reference wave on the observational plane (11) so as to produce an image.