TEM Strain Measurement via Precession Electron Diffraction
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Solution Overview
Problem
Current methods for measuring strain in materials using electron microscopy suffer from systematic errors due to dynamical diffraction effects, which limit precision and accuracy, especially in samples with thickness variations and bending, making it difficult to achieve high spatial resolution and precise strain measurements.
Innovation Solution
The implementation of precession electron diffraction (PED) in a transmission electron microscope (TEM) with a Precession Device that applies time-dependent changes to the electron beam angle and image deflection coils to minimize dynamical diffraction effects, combined with numerical image warping algorithms to fit entire diffraction patterns and calculate strain distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional nanobeam diffraction (NBD) is used to measure strain, then spatial resolution can be achieved, but measurement precision deteriorates due to systematic errors from dynamical diffraction effects
Solution Approach 1:
The patent applies precession electron diffraction (PED) which changes the illumination conditions by precessing the electron beam through a small angle (typically 0.5-5 degrees). This parameter change in the diffraction geometry transforms the dynamical diffraction patterns into quasi-kinematical patterns, reducing the systematic errors that plague conventional NBD measurements and enabling precise strain measurements of better than 0.1%
Solution Approach 2:
The patent introduces an intermediary reference diffraction pattern (from an unstrained region) and uses image registration algorithms to compare and align it with strained region patterns. This intermediary approach allows the extraction of strain information by measuring relative shifts in diffraction spot positions, thereby achieving high precision strain measurements while accounting for experimental variations
2Measurement precision
If entire diffraction patterns are fitted to improve precision, then measurement accuracy improves, but device complexity increases due to image registration requirements
Solution Approach 1:
The patent replaces manual or simple automated spot position measurement with sophisticated image registration and pattern fitting algorithms. These computational methods automatically align reference and strained diffraction patterns, measure spot position shifts, and calculate strain tensors, thereby achieving high precision measurements while the computational complexity is managed through automated processing pipelines
3Measurement precision
If high spatial resolution is achieved with small field of view, then local strain can be measured, but productivity decreases due to limited area coverage
Solution Approach 1:
The patent measures strain at multiple discrete points (typically 3-5 spots) within the diffraction pattern, treating each spot as an independent measurement unit. This segmentation allows the extraction of multiple strain components (εxx, εyy, εxy) from a single diffraction pattern, thereby increasing the information yield and effective productivity without sacrificing spatial resolution or requiring larger field of view
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 enhances the precision and accuracy of strain measurements by reducing errors from dynamical diffraction, allowing for high spatial resolution and correlation of strain values with other sample details, and provides spatially registered compositional information.
Implementation Method 1
In PED, the incident electron beam is precessed at a relatively high frequency (10-1000 Hz) through a small (0.2-5 degrees) angle. This precession reduces the visible effects of dynamical diffraction
Implementation Method 2
The main systematic errors in measuring spot positions from conventional NBD patterns, and therefore in calculating strain within a material, arise from the fact that the diffraction spot intensities and centers of mass are strongly affected by dynamical electron diffraction
Implementation Method 3
Electron diffraction patterns offer the ability to measure the lattice parameters of crystalline materials
Data Source
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Figure 3
AI summary
A process for measuring strain is provided that includes placing a sample of a material into a TEM as a sample. The TEM is energized to create a small electron beam with an incident angle to the sample. Electrical signals are generated that control multiple beam deflection coils and image deflection coils of the TEM. The beam deflection control signals cause the angle of the incident beam to change in a cyclic time-dependent manner. A first diffraction pattern from the sample material that shows dynamical diffraction effects is observed and then one or more of the beam deflection coil control signals are adjusted to reduce the dynamical diffraction effects. One or more of the image deflection coil control signals are then adjusted to remove any motion of the diffraction pattern. A diffraction pattern is then collected from a strained area of the material after the adjusting step, and the strain is then determined from a numerical analysis of the strained diffraction pattern compared to a reference diffraction pattern from an unstrained area of the material.