TKD Pattern Correction via Magnetic Field Mapping
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Solution Overview
Problem
Transmission Kikuchi Diffraction (TKD) patterns are distorted by electron optics, particularly magnetic fields in electron microscopes, leading to non-linear diffraction bands that hinder accurate crystal orientation and phase determination.
Innovation Solution
A method that unmasks TKD patterns by using generalized trigonometric expressions to rotate and contract image points, effectively removing the influence of magnetic fields without requiring detailed knowledge of the magnetic field, allowing for high-precision indexing of Kikuchi patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic lenses are used to improve scanning resolution, then scanning resolution is improved, but TKD patterns become distorted with non-linear diffraction bands
Solution Approach 1:
The patent extracts and removes the distortion caused by magnetic lenses from the TKD pattern through a mathematical mapping process. The method separates the useful diffraction information from the harmful magnetic field distortion, allowing the pattern to be corrected while preserving the underlying crystal structure data.
Solution Approach 2:
The patent applies parameter changes by using a mapping function with parameters γ and φ that transform the distorted pattern coordinates. By adjusting these parameters, the method corrects the non-linear diffraction bands caused by magnetic lenses, converting them back to linear bands suitable for accurate crystal orientation determination.
2Reliability
If magnetic fields are present in the electron microscope, then electron beam focusing is improved, but diffraction bands become curved and indexing accuracy deteriorates
Solution Approach 1:
The patent introduces a mathematical mapping function as an intermediary between the distorted TKD pattern and the desired linear pattern. This intermediary transformation, defined by equations involving parameters γ and φ, mediates the conversion from curved diffraction bands to straight bands, enabling accurate indexing despite the presence of magnetic fields.
Solution Approach 2:
The patent replaces the mechanical/optical approach of eliminating magnetic fields with a mathematical computation approach. Instead of physically removing or shielding from magnetic fields, the method uses computational mapping to correct their effects, substituting a mathematical system for a physical modification.
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 improves the quality of TKD patterns by correcting distortions caused by magnetic fields, enabling accurate determination of crystal orientation and phase with high precision, even in the presence of magnetic lenses.
Implementation Method 1
Kikuchi diffraction can also reveal information on the strain in a material. In Kikuchi diffraction backscattered or transmitted electrons are diffracted by the periodic atomic lattice within the sample according to the Bragg condition before they exit the sample.
Implementation Method 2
Magnetic lenses are deliberately created in certain scanning electron microscopes with the aim to improve the scanning resolution of the electron beam. However, due to such magnetic lens, a residual magnetic field may exist in the SEM chamber that distorts the movements of the electrons.
Data Source
AI summary
The present invention refers to a method for improving a Transmission Kikuchi Diffraction, TKD pattern, wherein the method comprises the steps of: Detecting a TKD pattern (20b) of a sample (12) in an electron microscope (60) comprising at least one active electron lens (61) focusing an electron beam (80) in z-direction on a sample (12) positioned in distance D below the electron lens (61), the detected TKD (20b) pattern comprising a plurality of image points xD, yD and mapping each of the detected image points xD, yD to an image point of an improved TKD pattern (20a) with the coordinates x0, y0 by using and inverting generalized terms of the form xD=γ*A+(1−γ)*B and yD=γ*C+(1−γ)*D whereinγ=ZDwith Z being an extension in the z-direction of a cylindrically symmetric magnetic field BZ of the electron lens (61), and wherein A, B, C, D are trigonometric expressions depending on the coordinates x0, y0, with B and D defining a rotation around a symmetry axis of the magnetic field BZ, and with A and C defining a combined rotation and contraction operation with respect to the symmetry axis of the magnetic field BZ. The invention further relates to a measurement system, computer program and computer-readable medium for carrying out the method of the invention.