Coaxial Cathodoluminescence Microscope Optics for Large-Field Imaging
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Solution Overview
Problem
Existing scanning electron microscopes face challenges in integrating high numerical aperture reflective objectives within electromagnetic lenses, leading to degraded spatial resolution, limited field of view, and reduced collection efficiency of cathodoluminescence signals, especially in low light intensity conditions.
Innovation Solution
Position light optical elements coaxially within the electromagnetic objective lens, using a Schwarzschild reflective objective with concave and convex mirrors, and electron beam deflectors within the electromagnetic lens to minimize obstruction and aberrations, allowing for high numerical aperture and large field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large reflector is used to maintain good optical and mechanical performance, then the working distance increases, but the electron beam probe size increases
Solution Approach 1:
The reflective objective is nested within the electromagnetic objective lens structure. The light optical elements are positioned coaxially within the space occupied by electromagnetic optical elements, allowing the reflective objective to be integrated into the existing electron microscope column without increasing the overall working distance.
Solution Approach 2:
The patent transitions from a conventional side-mounted reflector configuration to a coaxial integration within the electromagnetic lens. This dimensional repositioning allows the light collection path to share the same axial space as the electron beam path, eliminating the need for a large working distance while maintaining optical performance.
2Reliability
If a reflector is inserted between the electromagnetic lens and sample, then cathodoluminescence collection is improved, but the electrical field for secondary electron extraction is blocked
Solution Approach 1:
The objective lens is segmented into distinct electromagnetic and optical functional zones. The electromagnetic elements focus the electron beam while the light optical elements collect cathodoluminescence, allowing both functions to operate independently without mutual interference.
Solution Approach 2:
The patent introduces an intermediary optical system that mediates between the sample and the detector. The light optical elements collect cathodoluminescence photons without interfering with the electron beam or secondary electron extraction, as they operate in a different physical domain (photons vs. electrons).
3Area of stationary object
If a parabolic or elliptical reflector is used, then the field of view is limited to a few micrometres, but positioning precision requirements increase
Solution Approach 1:
The coaxial reflective objective serves multiple functions simultaneously: it acts as both the electron beam path guide and the light collection objective. This multi-functionality eliminates the need for separate alignment systems and reduces positioning precision requirements while maintaining a large field of view.
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
Achieves high spatial resolution and efficient collection of cathodoluminescence signals over large areas without degrading electron microscope performance, even in low light conditions.
Implementation Method 1
an electromagnetic objective lens (5) arranged to generate a magnetic field for focusing the electron beam to a focal plane
Implementation Method 2
a reflective objective arranged around the path of the electron beam (9) within the electromagnetic objective lens (5) for collecting light from the sample (7)
Implementation Method 3
The light emitted by a specimen upon electron bombardment is called cathodoluminescence
Data Source
AI summary
A scanning electron microscope having an electron column positioned to direct an electron beam onto a sample the electron column having a vacuum enclosure; an electron source; and an electromagnetic objective lens positioned within the vacuum enclosure, the electromagnetic objective lens including a housing having an entry aperture at top surface thereof and an exit aperture at bottom thereof; an electromagnetic coil radially positioned within the housing; a light objective positioned within the housing and comprising a concave minor having a first axial aperture and a convex minor having a second axial aperture; an electron beam deflector positioned within the housing and comprising a first set of deflectors and a second set of deflectors positioned below the first set of deflectors, wherein the second set of deflectors is positioned below the first axial aperture and the first set of deflectors is positioned above the second set of deflectors.