Photocathode Electron Beam Apparatus Virtual Source
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Solution Overview
Problem
Current electron microscopes face limitations in achieving high resolution due to large electron beam spot sizes, which are not adequately addressed by existing technologies, leading to insufficient inspection capabilities.
Innovation Solution
The method involves engineering the shape of a point photocathode to minimize the virtual source size by configuring the emitted electrons to intersect at a region within the cathode, allowing for a smaller image of the virtual source to be focused onto a specimen, thereby reducing the electron beam spot size and improving resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermionic emission cathodes or point cathode emitters are used, then electron beam generation is achieved, but the electron beam spot size remains large (>10 μm for thermionic, limited by virtual source size for point cathodes), degrading inspection resolution
Solution Approach 1:
The patent changes the fundamental emission mechanism parameter from thermionic emission or field emission to photoelectric emission. By using a photocathode illuminated by photons, electrons are emitted with much lower energy spread and from a smaller effective source region, directly reducing the electron beam spot size and improving resolution without requiring complex demagnification optics
Solution Approach 2:
The patent replaces the conventional electron gun design with multiple demagnification stages and crossovers with a simplified photoelectric emission system. The photocathode directly produces a small virtual source that can be focused to a small spot without requiring extensive mechanical demagnification optics, reducing system complexity while achieving smaller spot sizes
2Length of moving object
If multiple demagnification stages and crossovers are used to reduce beam spot size, then electron beam spot size is reduced, but device complexity increases significantly
Solution Approach 1:
The patent substitutes the complex mechanical demagnification system with a photoelectric emission approach. The photocathode inherently produces electrons with small virtual source size due to the photoelectric effect's nature, eliminating the need for multiple demagnification stages and crossovers, thus reducing device complexity while maintaining small spot size
Solution Approach 2:
By changing the emission mechanism to photoelectric emission, the patent achieves small virtual source size without requiring complex optical demagnification. The photoelectric effect naturally produces electrons with well-defined trajectories and small effective source region, simplifying the overall electron optical system
3Quantity of substance
If high current density is extracted from point cathode emitters, then electron beam current is increased, but the high electric field causes metal atom diffusion and electromigration, leading to emitter failure and thermal runaway
Solution Approach 1:
The patent replaces the field emission mechanism (which relies on high electric fields causing atomic diffusion) with photoelectric emission. Photons illuminate the photocathode surface, providing energy to electrons without requiring high electric fields at the emitter apex, thereby eliminating electromigration and thermal runaway while maintaining high current density capability
Solution Approach 2:
By changing the emission mechanism from field emission to photoelectric emission, the patent eliminates the need for high electric fields at the cathode surface. The photoelectric effect allows high current density extraction without the damaging high fields that cause metal atom diffusion and electromigration, significantly improving emitter reliability and lifetime
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 enables the production of an electron beam apparatus with a micrometer to sub-nanometer spot size, simple design, lower production costs, and the ability to maintain high electron density or ultrafast pulses without degrading the spot size, resulting in enhanced inspection capabilities.
Implementation Method 1
irradiating a photocathode so that the photocathode emits electrons
Data Source
AI summary
A method suitable for preparing a specimen for inspection, the method comprising the steps of: irradiating a photocathode so that the photocathode emits electrons from a surface of the photocathode, wherein the emitted electrons each follow a trajectory, and the trajectories of the electrons are such that they can be extrapolated to intersect at a region within the photocathode, the region defining a virtual source, and wherein the photocathode comprises a rounded tip which has a radius of curvature; configuring the emitted electrons so that they form an electron beam; focusing the electron beam onto a specimen to form an image of the virtual source on the specimen. There is further provided a corresponding electron beam apparatus.