Aberration-Corrected Low Energy Electron Microscope with Dual Beam Illumination
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Solution Overview
Problem
Conventional Low Energy Electron Microscopes (LEEM) and Photoemission Electron Microscopes (PEEM) face limitations in spatial resolution, energy-filtered imaging, and charging effects when imaging insulating samples, due to spherical and chromatic aberrations, lack of energy-filtered capabilities, and difficulties in dual beam illumination.
Innovation Solution
An apparatus and method utilizing energy-dispersive beam separators and electron mirrors for aberration correction, monochromatic illumination, and dual beam illumination, which includes a monochromator and knife-edge plate for energy filtering, allowing for aberration-corrected, energy-filtered imaging of specimens with overlapping electron beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electron lenses are used for imaging, then the microscope can achieve high magnification, but spherical and chromatic aberrations deteriorate spatial resolution
Solution Approach 1:
The imaging system is divided into multiple independent electron mirrors (first electron mirror for energy filtering, second electron mirror for aberration correction) that can be individually optimized and adjusted. This segmentation allows each mirror to address specific optical defects without compromising the overall system performance.
Solution Approach 2:
The patent employs adjustable magnetic field strengths in the electron mirrors to dynamically correct for spherical and chromatic aberrations. By changing the magnetic field parameters, the system can optimize image quality for different imaging conditions and specimen types.
2Adaptability or versatility
If a broad energy range electron beam is used for illumination, then the microscope can image various specimen types, but energy-filtered imaging capability is lost
Solution Approach 1:
The first electron mirror acts as an intermediary energy-filtering element between the electron source and the specimen. It selects electrons within a specific energy range before they reach the specimen, enabling energy-filtered imaging while maintaining the ability to image various specimen types by adjusting the energy selection parameters.
3Device complexity
If single beam illumination is used, then the microscope structure is simple, but charging effects occur when imaging insulating samples
Solution Approach 1:
The patent combines multiple electron beams with different energy characteristics into a single illumination system. The first electron mirror enables dual beam illumination where one beam provides primary imaging and another compensates for charging effects on insulating samples, merging their functions to achieve both simple operation and effective charge neutralization.
4Ease of operation
If conventional beam separators are used, then the microscope can separate illumination and projection optics, but additional combination aberrations are introduced
Solution Approach 1:
The energy-dispersive beam separator uses adjustable magnetic field parameters to separate illumination and projection optics while compensating for introduced aberrations. By dynamically changing the magnetic field strength and configuration, the system can optimize beam separation without degrading image quality.
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 spatial and spectroscopic resolution, enables imaging of insulating specimens by mitigating charging effects, and provides detailed chemical and electronic state information, improving the overall imaging capabilities of LEEM/PEEM instruments.
Implementation Method 1
A first energy-dispersive beam separator deflects the low-energy electron beam towards an electrostatic lens
Implementation Method 2
The electrostatic lens is biased negatively to reflect the low-energy electron beam. The monochromatic high-energy beam passes through the negatively biased electrostatic lens
Implementation Method 3
The second electron mirror is configured to correct for one or more aberrations of the cathode objective lens and reflects the electron beam back into the second energy-dispersive beam separator
Implementation Method 4
A first electron beam source is configured to generate a high-energy electron beam, and passed through a monochromator utilizing an electron mirror and a knife-edge plate that removes the high and low energy tail from the propagating beam
Implementation Method 5
The cathode objective lens is configured to illuminate the specimen, and electrons scattered and emitted by the specimen form an electron beam with a range of energies
Data Source
AI summary
One embodiment relates to an apparatus for correcting aberrations introduced when an electron lens forms an image of a specimen and simultaneously forming an electron image using electrons with a narrow range of electron energies from an electron beam with a wide range of energies. A first electron beam source is configured to generate a lower energy electron beam, and a second electron beam source is configured to generate a higher energy electron beam. The higher energy beam is passed through a monochromator comprising an energy-dispersive beam separator, an electron mirror and a knife-edge plate that removes both the high and low energy tail from the propagating beam. Both the lower and higher energy electron beams are deflected by an energy-dispersive beam separator towards the specimen and form overlapping illuminating electron beams. An objective lens accelerates the electrons emitted or scattered by the sample. The electron beam leaving the specimen is deflected towards a first electron mirror by an energy-dispersive beam separator, which introduces an angular dispersion that disperses the electron beam according to its energy. A knife-edge plate, located between the beam separator and first electron mirror, is inserted that removes all of the beam with energy larger and smaller than a selected energy and filters the beam according to energy. One or more electron lenses focus the electron beam at the reflection surface of the first electron mirror so that after the reflection and another deflection by the same energy-dispersive beam separator the electron beam dispersion is removed. The dispersion-free and energy-filtered electron beam is then reflected in a second electron mirror which corrects one or more aberrations of the objective lens. After the second reflection, electrons are deflected by the magnetic beam separator towards the projection optics which forms a magnified, aberration-corrected, energy-filtered image on a viewing screen.