EELS/EFTEM Quadrupole Layout for Low-Aberration Wide-Range Spectra
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Solution Overview
Problem
Conventional Transmission Charged Particle Microscopes face significant aberrations, particularly in Large-Energy-Range Electron Energy-Loss Spectroscopy (LER-EELS) modes, which limit their ability to record wide energy-range spectra without substantial radiative damage to specimens and sub-optimal results due to chromatic aberrations.
Innovation Solution
The method involves exciting specific quadrupoles in the first and second series to deflect off-axis non-dispersive rays onto a paraxial path, focusing the energy-dispersed beam with a minimal number of quadrupoles, thereby minimizing aberrations and achieving higher ΔE/E ratios beyond conventional limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional quadrupole configurations are used in EELS/EFTEM modules, then the system can focus the beam and disperse energy, but chromatic aberrations and other quadrupole-associated aberrations significantly degrade measurement precision for large energy-range spectra
Solution Approach 1:
The patent divides the quadrupole system into two independent series: a first series for beam focusing and a second series for energy dispersion. This segmentation allows each series to be optimized for its specific function, reducing the cumulative aberrations that would occur in a conventional single quadrupole system. The first series handles focusing with minimal chromatic aberration, while the second series handles energy dispersion, thereby improving measurement precision for large energy-range spectra without being degraded by quadrupole-associated aberrations.
2Measurement precision
If more quadrupoles are added to improve focusing and dispersion, then beam control improves, but the number of aberration sources increases, degrading measurement precision
Solution Approach 1:
The patent segments the quadrupole functions into two independent series, where the first series is dedicated to focusing and the second series to energy dispersion. This functional segmentation allows for optimized beam control accuracy while limiting the total number of quadrupoles to exactly two, thereby avoiding the increase in aberration sources that would result from adding more quadrupoles in a conventional configuration.
3Adaptability or versatility
If conventional EELS/EFTEM modules are used, then the system can operate in standard modes, but the maximum energy range is limited by chromatic aberrations, restricting the spectral energy spread coverage
Solution Approach 1:
The patent employs two independent quadrupole series that can be operated in various combinations to achieve different operational modes. This segmentation enables the system to cover a maximum energy range of ±10% of the incident beam energy while maintaining spectral resolution, thereby improving adaptability and versatility for large energy-range spectra without being constrained by the chromatic aberration limits of conventional single-quadrupole modules.
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 significantly reduces quadrupole-associated aberrations, enabling satisfactory results for LER-EELS with improved spectral energy spread coverage and reduced radiative damage, as demonstrated by achieving ΔE/E ratios well above previous limits.
Implementation Method 1
a dispersing device, between said entrance plane and slit plane, for dispersing an incoming beam into an energy-dispersed beam with an associated dispersion direction
Implementation Method 2
A first series of quadrupoles between said dispersing device and slit plane; A second series of quadrupoles between said slit plane and image plane
Implementation Method 3
The term 'quadrupole' as referred to here refers to a lens element that produces a quadrupole (magnetic or electric) field when excited
Data Source
Figure 1
Figure 2~3A
Figure 3B~3C
AI summary
A method of using a Transmission Charged Particle Microscope comprising: - A specimen holder, for holding a specimen; - A source, for producing a beam of charged particles; - An illuminator, for directing said beam so as to irradiate the specimen; - An imaging system, for receiving a flux of charged particles transmitted through the specimen and directing it onto a sensing device; - A controller, for controlling at least some operational aspects of the microscope, in which method the sensing device is chosen to be an EELS/EFTEM module comprising: - An entrance plane; - An image plane, where in EELS mode an EELS spectrum is formed and in EFTEM mode an EFTEM image is formed; - A slit plane between said entrance plane and image plane, where in EFTEM mode an energy dispersed focus is formed; - A dispersing device, between said entrance plane and slit plane, for dispersing an incoming beam into an energy-dispersed beam with an associated dispersion direction; - A first series of quadrupoles between said dispersing device and slit plane; - A second series of quadrupoles between said slit plane and image plane, which dispersing device and quadrupoles are arranged along an optical axis, whereby, for a Cartesian coordinate system (X,Y,Z) in which said optical axis is disposed along Z, said dispersion direction is defined as being parallel to X, comprising the following steps: - In said first quadrupole series, exciting one or more quadrupoles so as to deflect an off-axis non-dispersive YZ ray leaving said dispersing device onto a path paraxial to said optical axis from said slit plane to said image plane; - In said second quadrupole series, exciting either: (a) A single quadrupole; or (b) A pair of adjacent quadrupoles, so as to focus said energy-dispersed beam onto said image plane.