Second-Order Focusing Toroidal Spectrometer for Electron Energy Resolution

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Solution Overview

Problem

Toroidal electron energy spectrometers have inferior energy resolution due to first-order focusing, which limits their ability to capture detailed energy spectra of scattered electrons and ions in Scanning Electron Microscopes, hindering nano-scale inspection and material analysis.

Innovation Solution

A 2π radian collection second-order focusing toroidal spectrometer design with an intermediate focus, allowing cancellation of spherical aberrations, and the use of a pre-focusing lens to improve energy resolution, enabling parallel energy acquisition and retarding/accelerating field operations without auxiliary lenses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If first-order focusing is used in toroidal spectrometers, then the structure is simpler and easier to manufacture, but the energy resolution deteriorates and becomes inferior to CMA

Engineering Contradiction:

Improvespectrometer structure simplicityVSAvoidenergy resolution

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the focusing order parameter from first-order to second-order focusing. This parameter change fundamentally improves the energy resolution by reducing spherical aberration effects, achieving resolution comparable to CMA while maintaining the toroidal structure's inherent advantages of 2π collection and rotational symmetry.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs an intermediate focus configuration in the r-z plane that utilizes the curved toroidal geometry to achieve second-order focusing. The spherical aberration contributions before and after the intermediate focus cancel each other due to the opposite signs of electrons with emission angles to either side of the central ray, thereby improving energy resolution without requiring auxiliary lenses.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Measurement precision

If CMA is used to achieve high energy resolution, then the energy resolution improves to 0.155%, but the transmission decreases to around 14% due to grid constraints

Engineering Contradiction:

Improveenergy resolutionVSAvoidelectron transmission

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent segments the toroidal spectrometer into two distinct regions separated by an intermediate focus: a first region before the intermediate focus and a second region after it. This segmentation allows spherical aberration contributions from each region to cancel each other, achieving high energy resolution without the transmission losses associated with CMA grids.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent converts the typically harmful spherical aberration into a beneficial effect by designing the system so that spherical aberration contributions from the two regions have opposite signs and cancel each other. This transforms what is normally a limiting factor into a mechanism that enables second-order focusing and high resolution without transmission penalties.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If second-order focusing is implemented to improve energy resolution, then the energy resolution improves to 0.146%, but the device complexity increases due to intermediate focus requirements

Engineering Contradiction:

Improveenergy resolutionVSAvoidspectrometer configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent designs the toroidal spectrometer to serve multiple functions simultaneously: the same electrostatic fields that define the toroidal geometry also create the intermediate focus and enable second-order focusing. The spectrometer can simultaneously record different emission energies with a parallel energy window of up to 15%, achieving multi-functionality without requiring separate auxiliary lenses or complex additional components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The toroidal spectrometer achieves second-order focusing through its own inherent geometry and electrostatic field configuration, without requiring external auxiliary lenses or additional focusing components. The intermediate focus is created naturally by the toroidal electrode structure itself, making the system self-sufficient and avoiding the complexity that would arise from adding separate focusing elements.

Inventive Principle:

Principle #25Self-service

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

The design achieves an energy resolution comparable to the Cylindrical Mirror Analyzer, with improved transmittance and ability to capture a broader energy band, enhancing the analytical capabilities of Scanning Electron Microscopes for nano-scale inspection.

Implementation Method 1

a first voltage source (34) electrically coupled to first deflection plate (30) biases the same to a first voltage (V1), and a second voltage source (36) electrically coupled to second deflection plate (32) biases the same to a second voltage (V2)

Methodology Applied

Scientific EffectElectrostatic field: Electric Field

Implementation Method 2

This allows for second-order spherical aberration contributions accumulated before and after the intermediate focus to cancel, since electrons with emission angles to either side of the central ray gain spherical aberration are of opposite sign

Methodology Applied

Scientific EffectSpherical aberration cancellation: Focusing