TEM Phase Plate Centering via Electron Beam Deflection
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Solution Overview
Problem
Existing methods for aligning optical elements in Transmission Electron Microscopes (TEMs) face challenges such as damage and contamination due to irradiation with unscattered electrons, which affects the Contrast Transfer Function (CTF) and image quality, especially for phase plates and other structures that extend close to the central beam.
Innovation Solution
The method involves deflecting the beam of unscattered electrons away from the optical elements during alignment to prevent irradiation, allowing for precise centering without damaging or charging the structures, and using holders with features to facilitate accurate positioning, such as circular apertures and deflectors to align the beam back onto the axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the phase plate is mechanically aligned to the required accuracy, then the alignment precision can be achieved, but the phase plate may be damaged due to thermal heating and contamination from high current density
Solution Approach 1:
The patent applies preliminary action by performing the alignment of the phase plate using deflected electron beams before the actual imaging process. The beam is deflected away from the phase plate during alignment, allowing precise positioning to be achieved before the beam is returned to its normal path, thus preventing thermal damage and contamination that would occur if alignment were performed with the full current beam.
Solution Approach 2:
The patent uses an intermediary approach by introducing a deflection mechanism that temporarily redirects the electron beam away from the phase plate during alignment. This intermediary action allows the alignment process to occur without the harmful effects of direct beam irradiation, while still enabling precise positioning through the use of alignment markers and deflection control.
2Reliability
If the phase plate is positioned close to the central beam to enhance CTF, then the contrast enhancement is improved, but the phase plate is more susceptible to damage and charging
Solution Approach 1:
The patent applies preliminary action by performing all alignment and positioning operations before the phase plate is exposed to the full current beam. The phase plate is positioned close to the central beam path for optimal contrast enhancement, but the beam is deflected away during the alignment process, allowing the plate to be placed in the optimal position without suffering damage or charging from high current density.
Solution Approach 2:
The patent implements periodic action by alternating between beam deflection states - deflecting the beam away from the phase plate during alignment and positioning operations, then returning the beam to its normal path during imaging. This periodic switching allows the system to achieve both high contrast enhancement (when beam is on axis) and protection from damage (when beam is deflected).
3Ease of operation
If mechanical alignment methods are used for optical elements, then the alignment process is simple, but the required accuracy of better than +/−0.25 μm is difficult to achieve
Solution Approach 1:
The patent replaces mechanical alignment methods with an electromagnetic deflection-based alignment system. Instead of relying solely on mechanical precision of mounting fixtures and manual positioning, the system uses electromagnetic deflectors to precisely control the electron beam position relative to alignment markers on the phase plate. This substitution of mechanical positioning with electromagnetic control enables achievement of the required sub-micrometer alignment accuracy.
Solution Approach 2:
The patent applies parameter changes by utilizing the deflection sensitivity of the electron beam to achieve fine positional adjustments. By changing the deflection parameters (beam angle, position, and focus) during alignment, the system can achieve precise positioning of the phase plate relative to the beam path, overcoming the limitations of mechanical alignment precision.
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 effectively prevents damage and contamination, enabling precise alignment of optical elements while enhancing the Contrast Transfer Function, leading to improved image quality and reduced charging effects.
Implementation Method 1
deflecting the beam of unscattered electrons away from the structure
Implementation Method 2
the phase plate inducing a phase difference between the central, undiffracted beam and the diffracted electrons
Implementation Method 3
an objective lens for guiding a beam of electrons to a sample
Implementation Method 4
In the diffraction plane (coincident with the back-focal plane of the objective lens when a parallel beam irradiates the sample) the electrons that passed the sample unhindered are all focused in one point
Data Source
AI summary
A method for adjusting or aligning one or more optical elements in a Transmission Electron Microscope (TEM) is disclosed. The TEM is equipped with an objective lens for guiding a beam of electrons to a sample, a diffraction plane in which at least a beam of unscattered electrons is focused and a structure to enhance the Contrast Transfer Function (CTF) which is situated in the diffraction plane or an image thereof.