STEM Precession Alignment Automation
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Solution Overview
Problem
Current methods for aligning a scanning transmission electron microscope (STEM) for precession electron diffraction (PED) mapping are hindered by sensitivity to misalignment, optical aberrations, and lengthy alignment procedures, which degrade the resolution and accuracy of PED data maps, especially when accessing larger precession tilt angles and faster scan rates.
Innovation Solution
An automated method for aligning a STEM involves generating an incident electron beam aligned with the optic axis, scanning it across discrete sample locations to acquire non-inclined and inclined signal distributions, and applying a cyclic azimuthal scanning protocol to determine azimuthal spatial alignment corrections, thereby minimizing beam displacement during precession and maintaining alignment for high spatial resolution PED mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual or automated alignment procedures are used to align STEM for PED mapping, then alignment can be achieved, but the procedures are lengthy and reduce productivity
Solution Approach 1:
The system performs self-alignment by automatically detecting the pivot point position and calculating correction signals without requiring manual intervention. The computer control system autonomously processes detector signals to determine alignment corrections, enabling the instrument to align itself rapidly and reproducibly.
Solution Approach 2:
The patent replaces manual mechanical alignment procedures with an automated computer-controlled system that uses electronic signal processing and feedback. Instead of manual adjustment of mechanical components, the system uses electronic correction signals applied to beam deflectors to achieve precise alignment automatically.
2Ease of operation
If precession alignment is performed using TEM imaging mode beam observation, then alignment can be achieved, but optical aberrations cause the image not to represent the actual beam, degrading measurement precision
Solution Approach 1:
The patent introduces an intermediary computational step that accounts for optical aberrations. Instead of directly using the distorted TEM image to determine alignment, the system calculates correction signals that compensate for the known optical aberrations, using the distorted image as an intermediate reference that is mathematically corrected to represent the actual beam position.
Solution Approach 2:
The system uses feedback from detector signals to continuously monitor and adjust beam position. The computer control system processes signals from detectors positioned to sense beam location and automatically applies correction signals to maintain accurate alignment, creating a closed-loop feedback system that compensates for optical distortions.
3Manufacturing precision
If smaller incident beam diameters and larger precession tilt angles are used to improve resolution, then spatial resolution increases, but sensitivity to misalignment increases, degrading reliability
Solution Approach 1:
The system performs preliminary alignment to precisely establish the pivot point position before acquiring PED mapping data. By completing the alignment procedure in advance with automated detection and correction, the system ensures that subsequent high-resolution measurements are performed with optimal alignment stability, preventing misalignment during data acquisition.
Solution Approach 2:
The patent implements continuous feedback monitoring during PED mapping acquisition to detect and correct any drift in beam position. The system uses detectors to monitor beam location in real-time and applies automatic correction signals to maintain alignment stability, ensuring reliable data collection even when using small beam diameters and large precession angles that are highly sensitive to misalignment.
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 rapid and reproducible acquisition of PED mapping data with increased speed and reduced user intervention, preserving alignment during data acquisition and improving the accuracy and resolution of PED maps by effectively counteracting beam displacement.
Implementation Method 1
The acquired signals can be used to generate a highly magnified image of the scanned sample area showing morphological, compositional and structural information. A suitably configured two-dimensional electron detector can acquire the angular distribution of electrons scattered from the sample. Such electron diffraction (ED) data can be analyzed to determine the local structure-crystalline phase, crystal orientation, strain, degree of crystallinity, etc.
Implementation Method 2
A suitably configured two-dimensional electron detector can acquire the angular distribution of electrons scattered from the sample
Implementation Method 3
The influence of dynamical diffraction can be suppressed using precession electron diffraction (PED), in which the incident beam is tilted off-axis, typically by of the order of 0.3 to 3 degrees, and rotated around the axial direction, defining a cone ideally having its apex (or 'pivot point') fixed on a discrete sample location. The inclination of the incident beam, averaged by azimuthal rotation, suppresses dynamical diffraction effects
Data Source
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AI summary
Methods are disclosed for automatically aligning a scanning transmission electron microscope (STEM) for acquisition of precession electron diffraction (PED) mapping data at high spatial resolution.