Schottky Electron Source Tip Geometry for Resolution and Brightness
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Solution Overview
Problem
Existing electron sources face challenges in maintaining high brightness and resolution at low acceleration voltage due to issues with radius of curvature and cone angle, leading to instability and limited duration of operation at low temperatures.
Innovation Solution
An electron source with a radius of curvature between 0.5 μm and 1 μm and a cone angle between 5° and (8/r)°, using a barium diffusion supply composed of a porous sintered metal and barium oxide, is designed to provide a stable and monochromatic electron beam for high-resolution imaging and elemental analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the radius of curvature of the electron source tip is increased to reduce chromatic aberration and improve resolution, then the brightness and current extraction efficiency decrease
Solution Approach 1:
The patent optimizes the radius of curvature parameter to a specific range (0.5-1 μm) that balances chromatic aberration reduction with brightness maintenance. This parameter optimization resolves the contradiction by finding the optimal value that satisfies both resolution and brightness requirements simultaneously.
2Illumination intensity
If the cone angle of the electron source is increased to improve brightness and current extraction, then the energy width increases and monochromaticity deteriorates
Solution Approach 1:
The patent optimizes the cone angle parameter within a specific range (5° to (8/r)°) to balance brightness enhancement with energy width control. This parameter optimization resolves the contradiction by finding the optimal cone angle that maintains both high brightness and good monochromaticity.
3Temperature
If barium is used as a diffusion source to achieve low work function and low operating temperature, then diffusion stability deteriorates and operational duration is limited
Solution Approach 1:
The patent uses a composite structure combining porous sintered metal (tungsten or nickel) with barium oxide as the diffusion source. The porous sintered metal matrix provides structural stability and controlled diffusion characteristics, while barium oxide supplies barium atoms. This composite material approach resolves the contradiction by maintaining low operating temperature through barium's low work function while achieving long-term diffusion stability through the robust sintered metal structure.
4Illumination intensity
If the radius of curvature is made small to increase brightness, then chromatic aberration due to Boersch effect increases and resolution decreases
Solution Approach 1:
The patent determines the optimal radius of curvature range (0.5-1 μm) that prevents excessive chromatic aberration from Boersch effect while maintaining sufficient brightness. This parameter optimization resolves the contradiction by avoiding both extremes (too small or too large radius) and finding the sweet spot that satisfies both brightness and resolution requirements.
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 configuration maintains high brightness and resolution at low acceleration voltage, enabling high-speed elemental analysis with improved stability and extended operational duration.
Implementation Method 1
using a barium diffusion supply composed of a porous sintered metal and barium oxide
Implementation Method 2
Schottky emission electron source... gives monochromatic, highly bright electron beams
Data Source
AI summary
To obtain a SEM capable of both providing high resolution at low acceleration voltage and allowing high-speed elemental distribution measurement, a SE electron source including Zr—O as a diffusion source is shaped so that the radius r of curvature of the tip is more than 0.5 μm and less than 1 μm, and the cone angle α of a conical portion at a portion in the vicinity of the tip at a distance of 3r to 8r from the tip, is more than 5° and less than (8/r)°. Another SE electron source uses Ba—O and includes a barium diffusion supply means composed of a sintered metal and a barium diffusion source containing barium oxide.