Aberration Correction in Electron Lenses via Beam Separator and Mirrors

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Solution Overview

Problem

Conventional Low Energy Electron Microscopes (LEEM) and Photoemission Electron Microscopes (PEEM) suffer from limited lateral resolution due to spherical and chromatic aberrations introduced by the cathode objective lens, which hinder achieving sub-nm resolution.

Innovation Solution

An apparatus and method utilizing a single energy-dispersive magnetic beam separator and two electron mirrors to correct aberrations, where the beam is deflected 90 degrees and focused at an achromatic plane, allowing symmetry to remove energy dispersion and correct chromatic and spherical aberrations, enhancing spatial resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a cathode objective lens is used to form an image in LEEM/PEEM, then the specimen can be imaged with low landing energy electrons, but spherical and chromatic aberrations are introduced that deteriorate spatial resolution

Engineering Contradiction:

Improvespatial resolutionVSAvoidspherical and chromatic aberrations

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent divides the optical path into multiple segments using a beam separator that separates the illumination and projection optics. This segmentation allows independent optimization of each optical path segment, enabling aberration correction in the projection optics without affecting the illumination optics configuration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary electron mirror system between the objective lens and the detector. This intermediary component serves as an aberration corrector that compensates for spherical and chromatic aberrations introduced by the cathode objective lens, thereby improving spatial resolution without changing the fundamental imaging mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If conventional electron mirrors are used in LEEM, then the optical path can be configured, but the system becomes complex and compact arrangement is difficult

Engineering Contradiction:

Improveoptical path configurationVSAvoidsystem compactness

Core Design Contradiction:

Device complexityVSVolume of moving object

Solution Approach 1:

The patent combines multiple functions into a single integrated electron mirror component that simultaneously serves as both an aberration corrector and an optical path redirector. This merging reduces the number of separate components needed, simplifying the overall system configuration and reducing the volume required for the optical path.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The electron mirror is designed with multi-functionality, serving as both an aberration correction element and a beam steering component. This universal design eliminates the need for separate aberration correctors and beam deflectors, reducing system complexity and compacting the optical arrangement.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 improves the spatial resolution of LEEM and PEEM, enabling sub-nm imaging by effectively correcting aberrations and allowing for energy-filtered, aberration-corrected imaging.

Implementation Method 1

a magnetic beam separator deflects the electron beam emitted from the specimen and magnified by a cathode objective lens towards a first electron mirror

Methodology Applied

Scientific EffectLorentz force: Lorentz Force

Implementation Method 2

An electron lens is configured to focus the dispersed electron beam at the reflection plane of a first electron mirror

Methodology Applied

Scientific EffectElectron lens focusing: Lens

Implementation Method 3

the reflected electron beam passes through the magnetic beam separator a second time and exits without energy dispersion

Methodology Applied

Scientific EffectElectron mirror reflection: Reflection

Implementation Method 4

a second electron mirror that is configured to correct for one or more aberrations of the cathode objective lens and reflect the electron beam back into the magnetic beam separator

Methodology Applied

Scientific EffectAberration correction:

Data Source

PatentUS11276549B1Compact arrangement for aberration correction of electron lenses

Publication Date: 2022.03.15 MANKOS MARIAN

AI summary

One embodiment relates to apparatus for correcting aberrations introduced when an electron lens images a specimen. A specimen is illuminated, and a cathode objective lens accelerates emitted or scattered electrons. The resulting electron beam is deflected by a magnetic beam separator that disperses the incoming electron beam according to its energy. The dispersed beam is focused at the reflection plane of an electron mirror. After this focusing, and a second deflection by the beam separator, the beam dispersion is removed. The dispersion-free beam is reflected in a second electron mirror which corrects aberrations of the cathode objective lens. The beam separator then deflects the beam towards projection optics which form a magnified, aberration-corrected image. When energy filtering is needed, a knife-edge plate is inserted between the beam separator and first electron mirror to remove electrons outside the selected range.Other embodiments are disclosed.