Pulsed CFE Electron Source with Fast Blanker for Ultrafast TEM
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Solution Overview
Problem
High beam currents in transmission electron microscopy (TEM) generate unsafe levels of X-ray radiation, making it challenging to achieve fast TEM applications with pulsed electron beams, as existing shielding methods are impractical at currents above 150 nA.
Innovation Solution
A charged particle beam system that modulates electron beams to produce both pulsed and continuous components, using a CPB source, lens, and beam blanker to control X-ray generation, allowing for selective attenuation and focusing to manage beam currents within safe X-ray limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high beam currents are used for fast TEM applications, then time resolution and beam brightness are improved, but unsafe levels of X-ray radiation are generated
Solution Approach 1:
The patent applies periodic action by using pulsed electron beams instead of continuous beams. The electron beam is delivered in short pulses (e.g., picosecond to nanosecond duration) at controlled repetition rates, which maintains high peak currents for excellent time resolution while reducing the average beam current to safe levels, thereby preventing excessive X-ray radiation generation.
Solution Approach 2:
The patent employs dynamic control of the electron beam parameters through a beam blanker that can rapidly switch the beam on and off. This dynamic modulation allows the system to achieve high peak currents when needed for imaging while maintaining low average currents for safety, effectively resolving the contradiction between speed performance and radiation safety.
2Stability of the object's composition
If continuous electron beam is used, then stable imaging is achieved, but X-ray radiation safety limits are exceeded
Solution Approach 1:
The system uses periodic pulsed beams with controlled duty cycles to maintain imaging stability. By optimizing the pulse width and repetition rate, the patent achieves sufficient temporal averaging for stable images while keeping the average beam current below safety thresholds, thus preventing excessive X-ray generation.
Solution Approach 2:
The patent changes the temporal parameters of the electron beam from continuous to pulsed mode. By adjusting pulse duration, repetition frequency, and peak current, the system maintains adequate signal stability for imaging while reducing the time-averaged beam current to safe levels, thereby resolving the contradiction between stability and safety.
3Speed
If pulsed electron beams with high peak currents are generated, then fast TEM performance is improved, but the complexity of beam control increases
Solution Approach 1:
The patent introduces a beam blanker as an intermediary device between the electron source and the specimen. This blanker simplifies the control architecture by providing a single point of rapid beam modulation, enabling precise pulsed beam delivery without requiring complex modifications to the entire electron optics system.
Solution Approach 2:
The patent replaces mechanical beam control methods with electromagnetic field-based control using the beam blanker. This substitution enables much faster switching speeds (electronic rather than mechanical), achieving the required picosecond to nanosecond pulse durations while maintaining system simplicity through electronic control circuits.
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
Enables improved time resolution and background suppression in Ultrafast TEM applications while maintaining average beam currents below X-ray radiation safety limits, even at high brightness and current levels.
Implementation Method 1
the CPB source comprises a field emitter such as a LaB6 nanorod
Implementation Method 2
A CPB lens is situated to receive the CPB from the CPB source and is coupled to a controller to produce the continuous CPB component by energizing the CPB lens
Implementation Method 3
the beam blanker comprises an electrostatic deflector or an RF resonant cavity
Implementation Method 4
the CPB source includes an extraction electrode situated to establish a beam current of at least one of the pulsed CPB component and the continuous CPB component
Data Source
AI summary
Charged particle beams (CPBs) are modulated using a beam blanker/deflector and an electrically pulsed extraction electrode in conjunction with a field emitter and a gun lens. With such modulation, CPBs can provide both pulsed and continuous mode operation as required for a particular application, while average CPB current is maintained within predetermined levels, such as levels that promote X-ray safe operation. Either the extraction electrode or the beam blanker/deflector can define CPB pulse width, CPB on/off ratio, or both.