Automated Aberration Measurement in Electron Microscopes
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Solution Overview
Problem
Measuring and controlling spherical and chromatic aberrations in electron microscopes, particularly in Low Energy Electron Microscopes (LEEM) and Photo Electron Emission Microscopes (PEEM), is a laborious and time-consuming process, often requiring single crystal samples and tedious calibration procedures, limiting routine calibration and correction of aberrations.
Innovation Solution
A method involving a dispersed energy distribution at the diffraction plane of the electron microscope, where an aperture is placed at a selected location to measure image displacement, determining aberration coefficients, and adjusting optical elements to control aberrations, using a processor to automate the process and eliminate the need for laborious calibration protocols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional methods are used to measure spherical and chromatic aberrations, then measurement accuracy can be achieved, but the process becomes laborious and time-consuming
Solution Approach 1:
The patent replaces manual mechanical measurement procedures with an automated computational method. Instead of physically adjusting components and manually recording measurements, the system uses a processor to automatically calculate aberration coefficients from captured images, substituting mechanical operations with computational processing.
Solution Approach 2:
The system performs self-measurement by capturing images of the electron beam itself and automatically processing these images to determine aberration coefficients. The microscope uses its own operational data (the beam images) to characterize its own aberrations without requiring external measurement tools or manual intervention.
2Reliability
If single crystal samples are used for measuring aberrations, then measurement reliability improves, but sample availability and ease of operation deteriorate
Solution Approach 1:
The patent extracts the measurement function from the sample itself. Instead of using a sample as the measurement medium, the system measures aberrations by analyzing the electron beam's own image characteristics. The sample is removed from the measurement process entirely, and the beam image alone provides sufficient information for aberration characterization.
Solution Approach 2:
The method makes the aberration measurement capability universal by eliminating the requirement for special single crystal samples. Any sample can be used during normal operation, and the same imaging system serves both for sample analysis and for aberration measurement, making the capability available in all operational conditions.
3Measurement precision
If chromatic aberration measurement is performed by varying electron beam energy, then aberration coefficients can be determined, but microscope re-alignment is required for each energy setting
Solution Approach 1:
The system performs preliminary alignment once, then uses this fixed alignment for measurements at multiple energy settings. By establishing the reference alignment beforehand and maintaining it constant throughout the measurement process, the system eliminates the need for repeated re-alignment operations at each energy setting.
Solution Approach 2:
The method establishes a periodic measurement approach where alignment is performed once as a preliminary step, then the same alignment configuration is used repeatedly for measurements at different energy levels. This periodic rather than continuous re-alignment reduces operational complexity while maintaining measurement accuracy.
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 method allows for efficient and automated measurement and control of spherical and chromatic aberrations, enabling routine calibration and correction without the need for single crystal samples or re-alignment of the microscope, thereby improving the operational efficiency of electron microscopes.
Implementation Method 1
Electron microscopes use a beam of accelerated electrons to illuminate a sample being tested to obtain high resolution images of the sample
Implementation Method 2
Due to multiple optical elements used to direct the electron beam and to form an image of the sample
Implementation Method 3
obtaining a dispersed energy distribution for electrons at a diffraction plane of the electron microscope
Implementation Method 4
placing an aperture at a selected location of the dispersed energy distribution in the diffraction plane
Implementation Method 5
measuring displacement of an image of the aperture in an image plane of the electron microscope
Data Source
AI summary
An electron microscope system and a method of measuring an aberration of the electron microscope system are disclosed. A method of controlling an aberration of an electron microscope includes obtaining a dispersed energy distribution for electrons at a diffraction plane of the electron microscope and placing an aperture at a selected location of the dispersed energy distribution in the diffraction plane. The method measures displacement of an image of the aperture in an image plane of the electron microscope for the selected location of the aperture. The method determines an aberration coefficient of the electron microscope from the measured displacement and the selected location of the aperture and alters a parameter of an element of the electron microscope to control the aberration of the electron microscope based at least in part on the determined aberration coefficient.