Beam Scanning Protocol for EELS and EDS Compositional Mapping
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Solution Overview
Problem
Analytical electron microscopy techniques like EELS and EDS face challenges in accurately determining the local chemical composition of crystalline materials due to channeling effects and signal variations caused by changes in the incident beam orientation, leading to difficulties in generating reliable compositional maps.
Innovation Solution
A beam scanning protocol is applied to maintain the electron beam's inclination and azimuthal angle constant over time, allowing for improved signal strength and reduced spurious variations, enabling enhanced compositional mapping in STEM, TEM, and SEM by optimizing the beam deflection control signals and using precession angles to suppress dynamical scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the incident beam is aligned close to a high symmetry crystallographic direction (zone axis) to obtain atomic resolution images or crystallographic information, then crystallographic information and atomic resolution are improved, but channeling effects cause significant changes in peak intensities (up to 20% variation with 1 degree orientation change) and reduce the overall intensity of EELS and EDS peaks relative to background
Solution Approach 1:
The patent applies periodic oscillation of the incident electron beam around the zone axis at a frequency of 50-200 Hz. This periodic action averages out the channeling effects that cause intensity variations, stabilizing the spectral peaks while maintaining the beneficial crystallographic alignment for atomic resolution imaging and crystallographic information acquisition.
2Measurement precision
If the incident beam orientation is changed by even one degree, then the relative composition measurement changes by as much as 20%, but maintaining precise beam orientation control is difficult due to electron optical instabilities and sample drift during extended data collection periods
Solution Approach 1:
By implementing continuous periodic oscillation of the beam orientation, the system transforms the difficult problem of maintaining precise static beam orientation into a more robust dynamic solution. The oscillation frequency (50-200 Hz) is high enough to average out slow drifts and instabilities, making the measurement less sensitive to electron optical variations and sample drift during extended data collection.
3Reliability
If the beam scanning protocol is applied to maintain constant beam inclination and azimuthal angle, then signal strength is improved and spurious variations are reduced, but additional beam control mechanisms and protocols are required
Solution Approach 1:
The periodic oscillation protocol provides a systematic method to maintain constant average beam inclination and azimuthal angle during data acquisition. By oscillating at 50-200 Hz, the system achieves signal stabilization and reduction of spurious variations while using standard beam control mechanisms, avoiding the need for 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
This approach enhances the accuracy and reliability of compositional mapping by stabilizing signal strength and reducing noise, allowing for precise quantitative analysis of crystalline and polycrystalline materials, even when the beam orientation is close to a high symmetry crystallographic direction.
Implementation Method 1
Though these two techniques originate in inelastic scattering phenomena, the processes by which the incident high energy electron beam excites bound state electrons within the sample
Implementation Method 2
energy dispersive x-ray spectroscopy ('EDS') relies on measurements of the energy distribution of x-rays emitted from regions of the sample exposed to the incident electron beam
Implementation Method 3
the coherent scattering by the periodic potential of the crystal (so-called elastic scattering) can strongly affect the peak intensities measured in EELS or EDS
Implementation Method 4
In some circumstances, these 'channeling' effects can be exploited to provide information about the location, on an atomic scale, of chemical species within a crystal structure
Data Source
AI summary
A method and system are disclosed for improving characteristic peak signals in electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDS) measurements of crystalline materials. A beam scanning protocol is applied which varies the inclination, azimuthal angle, or a combination thereof of the incident beam while spectroscopic data is acquired. The method and system may be applied to compositional mapping.