Wien Filter Beam Optics for Reduced Boersch Effect
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Solution Overview
Problem
The Boersch effect, which causes an increase in energy spread due to Coulomb interactions between charged particles in a beam, limits the energy resolution of charged particle beam sources, particularly in transmission electron microscopy and microanalysis, necessitating improved components and methods to reduce this effect.
Innovation Solution
A charged particle optical device incorporating a Wien filter with a specific excitation parameter (φ > 3π/4) and an optical element to focus the beam, along with a selector at a crossover plane, is used to disperse and narrow the energy distribution of the charged particle beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a charged particle beam is used for TEM imaging and microanalysis, then detailed information at the atomic scale can be obtained, but the Boersch effect causes an increase in energy spread which limits energy resolution
Solution Approach 1:
The patent changes the excitation parameter φ of the Wien filter to a specific range (greater than 3π/4, preferably between π and 3π/2, most preferably about 4.3) to optimize the dispersion of charged particles by energy. This parameter change reduces the Boersch effect and improves energy resolution of the beam
Solution Approach 2:
The patent introduces a Wien filter as an intermediary device between the charged particle source and the sample. The Wien filter disperses particles by energy in a dispersion plane parallel with the beam axis, and when operated at the optimized excitation parameter, it reduces the harmful Boersch effect while maintaining beam quality
2Quantity of substance
If the beam current is increased to improve signal strength, then more particles are available for analysis, but the Boersch effect increases due to stronger Coulomb interactions between particles
Solution Approach 1:
By optimizing the excitation parameter φ of the Wien filter, the patent reduces the Boersch effect even at higher beam currents. The specific parameter range (φ > 3π/4) minimizes Coulomb interaction effects, allowing higher beam currents to be used without proportionally increasing the Boersch effect
Solution Approach 2:
The Wien filter is positioned upstream in the beam path to preemptively reduce the Boersch effect before the beam reaches the sample. By dispersing particles by energy and optimizing the excitation parameter, the filter counteracts the harmful Coulomb interactions before they can significantly broaden the energy distribution
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 configuration significantly reduces the Boersch effect, improving energy resolution and allowing for precise measurement of energy-dependent material properties, enhancing imaging and microanalysis capabilities, especially in Electron Energy Loss Spectroscopy (EELS).
Implementation Method 1
The Wien filter can be configured to disperse particles of a beam of charged particles by energy in a dispersion plane. The dispersion plane can be parallel with the beam axis.
Implementation Method 2
The optical element can be configured to focus the beam of charged particles toward the beam axis.
Implementation Method 3
The selector can be disposed on the beam axis at a position substantially corresponding to a third crossover plane downstream of the optical element.
Data Source
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AI summary
The present disclosure describes systems, methods, algorithms, and non-transitory media storing computer-readable instructions for reducing the Boersch effect using dispersive optics, in various embodiments. A charged particle optical device can include a Wien filter disposed on a beam axis. The Wien filter can be configured to disperse particles of a beam of charged particles by energy in a dispersion plane. The dispersion plane can be parallel with the beam axis. The device an include an optical element disposed on the beam axis downstream of the Wien filter. The optical element can be configured to focus the beam of charged particles toward the beam axis. The device can also include a selector. The selector can be disposed on the beam axis at a position substantially corresponding to a third crossover plane downstream of the optical element.