Electron Diffraction Holography With Bifocal Beams for Phase Retrieval
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Solution Overview
Problem
Current transmission electron microscopy (TEM) systems operating in electron diffraction mode struggle to obtain full exit wave information, including both amplitude and phase, due to limitations in recording phase information, which restricts the types of objects that can be effectively imaged, and existing electron holography setups are unable to generate results from electrons detected in the diffraction plane.
Innovation Solution
The method involves forming a first and second electron beam with different focal planes using a bifocal beamformer, where the first beam is focused near the sample and the second beam is focused in the diffraction plane, allowing for the generation of a diffraction hologram that provides both phase and amplitude information by detecting their interference pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TEM systems operate in electron diffraction mode to study crystalline materials, then crystallographic information can be obtained, but phase information is lost and only intensity values are recorded
Solution Approach 1:
The patent introduces an electron biprism as an intermediary element that superimposes the electron diffraction pattern with a reference electron wave. This reference wave carries phase information that interferes with the diffracted electrons, creating an interference pattern that encodes both amplitude and phase data. The biprism acts as a mediator that transfers phase information from the invisible electron wave to a detectable interference pattern.
Solution Approach 2:
The patent applies different focal properties to different regions of the electron beam system. Specifically, it creates two distinct focal planes: one for the object beam that passes through the specimen and another for the reference beam. This local differentiation of focal properties enables the reference beam to remain coherent while the object beam carries specimen information, allowing phase retrieval without compromising crystallographic measurement precision.
2Loss of information
If off-axis holography is used to obtain full exit waves, then both intensity and phase information can be obtained, but it can only be applied where the specimen is imaged onto the camera, not in diffraction mode
Solution Approach 1:
The patent creates a universal electron holography method that functions in both imaging mode and diffraction mode. By using the electron biprism to superimpose reference and object waves in the diffraction plane, the system achieves full exit wave retrieval (intensity and phase) regardless of whether the specimen is imaged or diffracted. This multi-functional approach eliminates the restriction that prevented off-axis holography from being applied in diffraction mode.
3Measurement precision
If diffraction patterns are collected while continuous tilting of the crystal is performed, then 3D potential distribution can be reconstructed, but data collection time increases
Solution Approach 1:
The electron biprism serves as a mediator that captures complete phase and amplitude information in a single diffraction pattern. This eliminates the need for extensive tilting series traditionally required for 3D reconstruction, as the full exit wave information can be retrieved directly from the interference pattern, significantly reducing data collection time while maintaining measurement 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 approach enables the determination of phase and amplitude of diffraction patterns, allowing for the retrieval of the full exit wave and 3D information of specimens, even for unknown structures, enhancing the imaging capabilities of TEM systems.
Implementation Method 1
An interference pattern of the first electron beam and the diffracted second electron beam is then detected in the diffraction plane
Data Source
AI summary
Methods for using electron diffraction holography to investigate a sample, according to the present disclosure include the initial steps of emitting a plurality of electrons toward the sample, forming the plurality of electrons into a first electron beam and a second electron beam, and modifying the focal properties of at least one of the two beams such that the two beams have different focal planes. Once the two beams have different focal planes, the methods include focusing the first electron beam such that it has a focal plane at or near the sample, and focusing the second electron beam so that it is incident on the sample, and has a focal plane in the diffraction plane. An interference pattern of the first electron beam and the diffracted second electron beam is then detected in the diffraction plane, and then used to generate a diffraction holograph.