Environmental Cell Transparent Foil for SEM Secondary Radiation Detection
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Solution Overview
Problem
Current environmental cells in Scanning Electron Microscopes (SEMs) face challenges such as sample charging, reduced signal-to-noise ratio due to 'skirting effect', complex design, and interference from electrical connections, which hinder efficient detection of secondary radiation and result in longer scan times and image deterioration.
Innovation Solution
A simpler environmental cell design that allows for larger detection angles of secondary radiation by making part of the cell transparent to electrons, using a thin foil supported by a carrier, and admitting gases to adjust pressure and reduce charging, while maintaining a standard BSE detector outside the cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small aperture is used in the diaphragm to limit gas escaping, then the pressure in the environmental cell can be maintained, but the detection of secondary radiation is limited to only radiation passing through the aperture
Solution Approach 1:
The environmental cell is divided into two separate volumes: the sample volume where secondary radiation is generated, and the detector volume where detection occurs. The diaphragm with aperture serves as the boundary between these volumes. This segmentation allows the aperture to be optimized for pressure control while the detector can be positioned to receive radiation from a broader angular range, resolving the contradiction between pressure maintenance and detection capability.
2Object-affected harmful factors
If the diaphragm is electrically isolated to enable electric field formation for gas-cascade current, then charging is reduced, but the gas-cascade current is small requiring slow scan rates
Solution Approach 1:
The detection function is extracted from the environmental cell and placed in a separate detector positioned outside the cell. This eliminates the need for electrical isolation of the diaphragm and the associated gas-cascade current measurement system. The detector can operate at high scan rates without the limitations of small current measurement, while the environmental cell maintains pressure control through the aperture.
Solution Approach 2:
The aperture in the diaphragm serves as an intermediary element that allows controlled gas flow between the environmental cell and the vacuum system while also serving as the interface for secondary radiation detection. This intermediary approach eliminates the need for complex electrical isolation and gas-cascade current measurement, enabling both charging reduction and high-speed imaging.
3Device complexity
If a thin foil is used to make the cell transparent to electrons, then detection angles are increased, but the foil may be fragile and difficult to support
Solution Approach 1:
A thin foil is used as the diaphragm material to make the environmental cell transparent to secondary radiation, enabling detection over a wide angular range. The foil is supported by a rigid frame or mounting structure that provides mechanical strength while maintaining the thinness required for radiation transparency. This approach resolves the contradiction between achieving wide detection angles and maintaining structural integrity.
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 enhances image quality by reducing charging, improving signal-to-noise ratio, and simplifying the cell design, allowing for faster imaging and reduced interference, while maintaining high resolution and flexibility in gas pressure adjustments.
Implementation Method 1
A part 8 of the material of the vacuum enclosure is transparent to e.g. back-scattered electrons, so that said back-scattered electrons emerging from the sample 6 reach the detector 5 to be detected
Implementation Method 2
some of the atoms or molecules in the gas will become ionized by interaction with primary of secondary radiation, and these ionized atoms or molecules will drift to the charged parts of the sample and neutralize said charge
Implementation Method 3
The aperture is sufficiently small to limit the amount of gas escaping from the small volume to an amount that is acceptable to the SEM's vacuum system
Implementation Method 4
a much lower pressure between the aperture and the SEM column
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The invention relates to an environmental cell for use in e.g. an electron microscope. The environmental cell shows an aperture (15) for passing the beam produced by the electron microscope to a sample (6) placed inside the environmental cell. The environmental cell according to the invention is characterized in that a part of the environmental cell (14) is transparent to secondary radiation such as back-scattered electrons or X-rays. This enables the detection of this radiation by a detector placed outside the environmental cell and thus a much simpler construction of the cell.