Electron Microscope Aberration Measurement via Coma Introduction
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Solution Overview
Problem
Accurate measurement of aberrations in scanning transmission electron microscopes is hindered by axial disagreements between the objective lens and detector axes, leading to apparent aberrations that complicate the calculation of original low-order aberrations.
Innovation Solution
Introducing a coma aberration to the objective lens and measuring the aberration before and after its introduction allows for the determination of the optical axis position on the detector plane, thereby aligning the axes and isolating the original aberration from apparent aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If aberration measurement is performed using geometrical aberration in a scanning transmission electron microscope, then the aberration of the objective lens can be measured, but apparent aberrations occur due to axial disagreement between the optical axis of the objective lens and the axis of the detector, leading to inaccurate measurement results
Solution Approach 1:
The patent introduces a coma aberration as an intermediary element to measure the axial disagreement between the objective lens optical axis and detector axis. By deliberately adding this known aberration and observing its effect on the measured aberration coefficients, the system can calculate the axial offset and correct the measurement results, thereby eliminating the apparent aberrations caused by misalignment
Solution Approach 2:
The patent changes the aberration parameters of the objective lens by deliberately introducing a coma aberration with a specific coefficient. This parameter change allows the system to observe how the aberration coefficients vary with the added coma, enabling the calculation of the axial disagreement and subsequent correction of the measurement accuracy
Data Source
AI summary
An aberration measurement method for an objective lens in an electron microscope including an objective lens which focuses an electron beam that illuminates a specimen, and a detector which detects an electron beam having passed through the specimen, includes: introducing a coma aberration to the objective lens; measuring an aberration of the objective lens before introducing the coma aberration to the objective lens; measuring an aberration of the objective lens after introducing the coma aberration to the objective lens; and obtaining a position of an optical axis of the objective lens on a detector plane of the detector based on measurement results of the aberration of the objective lens before and after introducing the coma aberration.