STEM Beam Deflection for Image-Diffraction Angle Alignment
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Solution Overview
Problem
In scanning transmission electron microscopes, accurately determining the relative rotational angle between the image plane and the diffraction plane is challenging due to the complexities of image rotation caused by both the image-forming system lens and scan rotation, which hinders the association of real-space and reciprocal-space information.
Innovation Solution
A method involving a deflector to shift and tilt the electron beam, acquiring specific STEM images before and after these operations, and calculating the relative rotational angle based on these images to correct for the rotational discrepancies, allowing precise alignment of the image and diffraction planes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If scan rotation is performed to change the observation field direction, then the imaging flexibility is improved, but the determination of relative rotational angle between image plane and diffraction plane becomes difficult
Solution Approach 1:
The patent applies preliminary action by performing the beam shifting and tilting operations before acquiring the STEM images. This allows the system to establish a known reference state and then measure the rotational angle based on the known transformations applied, making the measurement feasible even after scan rotation has been performed.
Solution Approach 2:
The patent uses the deflector as an intermediary device to introduce known shifts and tilts in the electron beam. By using this intermediary component, the system can indirectly measure the relative rotational angle through the known transformations it imposes on the beam, rather than attempting to measure the angle directly.
2Measurement precision
If both image-forming system lens rotation and scan rotation are considered, then the accuracy of real-space and reciprocal-space association can be improved, but the complexity of the measurement system increases
Solution Approach 1:
The patent segments the measurement process into distinct steps: first shifting the beam, then tilting it, and acquiring images at each stage. This segmentation allows each transformation to be independently controlled and measured, simplifying the overall complex measurement task into manageable sequential operations.
Solution Approach 2:
The patent changes physical parameters of the electron beam (position and angle) in controlled steps using the deflector. By systematically varying these parameters and observing the resulting image changes, the system can determine the relative rotational angle without requiring complex additional hardware.
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
Enables easy and accurate measurement of the relative rotational angle, facilitating the association of real-space and reciprocal-space information, thereby improving analysis results in scanning transmission electron microscopy.
Implementation Method 1
a deflector that deflects an electron beam with which a specimen is illuminated
Implementation Method 2
a detector that is capable of detecting a scattering azimuth angle of electrons scattered by an electromagnetic field of the specimen
Data Source
AI summary
A method of measuring a relative rotational angle includes: shifting an electron beam on a specimen plane by using a deflector; tilting the electron beam with respect to the specimen plane by using the deflector; acquiring a first STEM image including information of a scattering azimuth angle and a second STEM image not including the information of the scattering azimuth angle, before the shifting and the tilting; acquiring a third STEM image including the information of the scattering azimuth angle and a fourth STEM image not including the information of the scattering azimuth angle, after the shifting and the tilting; and obtaining the relative rotational angle based on the first STEM image, the second STEM image, the third STEM image and the fourth STEM image.