Electrostatic Lens Design for Wide-Angle Atom Probe Aberration Control
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Solution Overview
Problem
Wide Angle Laser Tomographic Probes face challenges in achieving high mass resolution while maintaining a large analysis angle and long time of flight, due to spherical aberrations caused by strong focusing, which results in indeterminate ion trajectories and reduced detection efficiency.
Innovation Solution
A tomographic atom probe design featuring an electrostatic lens with three electrodes, where the distance between the sample and detector is greater than 2.75 times the detector diameter, and specific potential configurations to minimize spherical aberrations, allowing for increased analysis length and mass resolution without reducing the acceptance angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance L between the sample and detector is increased to increase time of flight and mass resolution, then mass resolution is improved, but a large part of the divergent ion beam escapes the detector
Solution Approach 1:
An electrostatic lens system is introduced as an intermediary device between the sample and detector. This lens comprises multiple electrodes (extractor, intermediate, and focusing electrodes) that generate electric fields to focus the divergent ion beam onto the detector surface, enabling efficient detection even at increased distances L > 2.75D
Solution Approach 2:
The potentials of the extractor electrode (V1), intermediate electrode (V2), and focusing electrode (V3) are optimized to create specific electric field configurations. By adjusting these voltage parameters, the system achieves strong focusing capability that counteracts beam divergence, allowing increased distance L while maintaining detection efficiency
2Quantity of substance
If strong focusing is applied using an Einzel lens to focus the ion beam on the detector, then detection efficiency is improved, but spherical aberration appears which produces parasitic effects on external trajectories
Solution Approach 1:
The electrostatic lens is divided into multiple independent electrodes (extractor, intermediate, and focusing electrodes) that can be independently controlled. This segmentation allows optimization of each electrode's function: the extractor accelerates ions, the intermediate electrode shapes the field, and the focusing electrode provides strong focusing while minimizing aberrations
Solution Approach 2:
Different regions of the ion beam are treated differently by the segmented electrode system. The electric field configuration is optimized to provide appropriate focusing strength for different trajectory angles, reducing spherical aberration effects on external trajectories while maintaining strong focusing for central trajectories
3Quantity of substance
If the analysis angle is increased to improve detection efficiency, then ion detection efficiency is improved, but mass resolution decreases due to reduced time of flight
Solution Approach 1:
The system decouples the relationship between acceptance angle and time of flight by introducing the spatial dimension through the electrostatic lens. The lens focuses ions from different angles onto the detector while maintaining a long flight path L > 2.75D, allowing large acceptance angles without sacrificing time of flight duration
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 significantly increases the analysis length and mass resolution by at least a factor of two, while maintaining the acceptance angle, effectively addressing the issue of spherical aberrations and improving the detection efficiency of ion trajectories.
Implementation Method 1
the respective potentials of the sample, of the first electrode of the lens and of the detector are such that the ions coming from the sample mounted on the sample holder are attracted to the first electrode and to the detector
Implementation Method 2
An electrostatic lens composed of three electrodes, a first electrode or extractor, arranged near the sample, a second electrode, intermediate, and a third electrode, arranged between the intermediate electrode and the detector
Implementation Method 3
Almost all of the path of the ions is thus carried out in a so-called 'field-free' space
Implementation Method 4
an essential parameter for obtaining a fine and precise measurement of the characteristics of the ions detected by an atomic probe, is the measurement of the time of flight of the ions detected
Data Source
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AI summary
The invention pertains to improvements in the mass resolution of wide-angle tomographic atomic probes. The invention comprises an atomic probe including, in addition to a sample-holding device and to detectors remote from each other by a distance L and enclosed in a housing, an electrostatic lens of the Einzel type made of three electrodes arranged inside the housing between the sample and the detector and to which electric potentials are applied in order to generate an electric field that strongly focalises the ion beam emitted by the sample under test during the probe operation. According to the invention, the geometry of the electrodes is defined accurately in order to substantially limit the spherical aberration effects undergone by the Einzel lens on the ion beam, of which the spherical aberration is particularly important when the lens is strongly polarised. The invention can particularly be used for atomic probes referred to as “3D atom probes.”