STEM Aperture Alignment Using Voltage-Shift Image Deviation
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Solution Overview
Problem
Existing methods for aligning the aperture in a scanning transmission electron microscope require forming a Ronchigram in an amorphous region of the specimen each time, which is inefficient and time-consuming.
Innovation Solution
A method and apparatus that aligns the aperture by obtaining first and second STEM images at different acceleration voltage or excitation current values, allowing the aperture to be aligned without moving the image center, thereby eliminating the need to repeatedly form Ronchigrams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the aperture is aligned by forming a Ronchigram in the amorphous region of the specimen each time, then the aperture can be aligned with the Ronchigram center, but the process becomes inefficient and time-consuming
Solution Approach 1:
The patent performs preliminary alignment by obtaining STEM images at different acceleration voltage or excitation current values before final aperture insertion. This preliminary action establishes the correct aperture position based on image position deviation, eliminating the need to repeatedly form Ronchigrams during subsequent alignment operations. The alignment state is prepared in advance using voltage/current variations rather than requiring repeated Ronchigram formation.
2Ease of operation
If the aperture is aligned repeatedly by inserting and checking the Ronchigram, then the alignment can be adjusted, but the operation becomes complex and inefficient
Solution Approach 1:
The patent replaces the mechanical/optical Ronchigram formation and visual checking process with an automated image-based alignment method. Instead of mechanically inserting the aperture and visually checking Ronchigrams, the system uses STEM images captured at different voltage/current values, calculates position deviation automatically, and determines the required aperture movement. This substitution of mechanical/optical procedures with automated image processing significantly improves operational ease and efficiency.
3Reliability
If the center of the aperture is aligned with the center of the Ronchigram using conventional methods, then the aberration of the illumination system is reduced, but the process requires frequent Ronchigram formation
Solution Approach 1:
The patent changes the alignment approach by utilizing variations in acceleration voltage or excitation current as the basis for determining aperture position. Instead of relying on Ronchigram formation, the system captures STEM images at different voltage/current parameters, calculates the position deviation between images, and uses this deviation to determine the required aperture movement. This parameter-based alignment method achieves the same goal of reducing illumination system aberration while eliminating repeated Ronchigram formation.
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
Facilitates easy and efficient alignment of the aperture with the Ronchigram center, reducing the need for frequent Ronchigram formation and enhancing the alignment process.
Implementation Method 1
an acceleration voltage for accelerating the electron beam
Implementation Method 2
an optical system that has a condenser lens, an aperture, and an objective lens and forms an electron probe by condensing the electron beam
Data Source
AI summary
A scanning transmission electron microscope includes an electron source that generates an electron beam, an optical system that has a condenser lens, an aperture, and an objective lens and forms an electron probe by condensing the electron beam generated by the electron source, and a control unit that controls the electron source and the optical system. The control unit performs processing of: inserting the aperture into a path of the electron beam; setting the acceleration voltage to a first voltage value and obtaining a first STEM image, in a state in which the aperture is inserted; setting the acceleration voltage to a second voltage value that is different from the first voltage value and obtaining a second STEM image, in a state in which the aperture is inserted; and moving the aperture based on position deviation between the first STEM image and the second STEM image.