Hexaboride Schottky Emitter for Stable High-Current Electron Beam
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Solution Overview
Problem
Current electron sources, such as cold field emitter and Schottky emitter electron sources, face issues with chromatic aberration, low spatial resolution, and instability due to gas adsorption, making them unsuitable for applications requiring high current density and long-term stability in electron beam devices like scanning electron microscopes.
Innovation Solution
A Schottky emitter electron source is developed using a columnar chip of hexaboride single crystal with a cone-shaped tip end having a (310) crystal face, processed by electropolishing and electric field evaporation, and integrated with a metal pipe and filament, allowing for stable high-current emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a cold field emitter electron source is used, then monochromaticity is improved, but stability deteriorates due to gas adsorption
Solution Approach 1:
The invention changes the operational parameter from room temperature (cold field emitter) to elevated temperature (900-1250°C), transforming the electron emission mechanism from pure field emission to Schottky emission. This parameter change simultaneously achieves good monochromaticity (energy full width at half maximum of 0.2-0.4 eV) and long-term stability by preventing gas adsorption through thermal effects
2Productivity
If a Schottky emitter electron source is used, then current density is improved, but spatial resolution deteriorates due to chromatic aberration
Solution Approach 1:
The invention optimizes the temperature parameter to a specific range (900-1250°C) and uses a hexaboride single crystal with a (310) crystal face to achieve a balance between current density and energy spread. This results in a smaller energy full width at half maximum (0.2-0.4 eV) compared to conventional Schottky emitters, reducing chromatic aberration and improving spatial resolution while maintaining high current density capability
3Reliability
If a thermal emitter electron source is used, then stability is improved, but luminance deteriorates due to large energy full width
Solution Approach 1:
The invention changes the emission mechanism from thermal emission to Schottky emission by applying an electric field to a heated hexaboride single crystal. This produces a smaller energy full width at half maximum (0.2-0.4 eV) compared to thermal emitters, thereby increasing luminance (radiation angle current density) while maintaining the stability benefits of heated operation
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
The solution provides a novel electron source with improved monochromaticity, long-term stability, and high current density, enabling high-resolution and long-term stable operation in electron beam devices, particularly suitable for scanning electron microscopes.
Implementation Method 1
The thermal emitter electron source heats a filament of tungsten (W) processed into a hairpin shape to approximately 2500° C., and causes electrons thermally excited in a W solid to cross an energy barrier having a work function φ
Implementation Method 2
processed by electropolishing and electric field evaporation
Implementation Method 3
processed by electropolishing and electric field evaporation
Data Source
AI summary
The invention provides an electron source including a columnar chip of a hexaboride single crystal, a metal pipe that holds the columnar chip of the hexaboride single crystal, and a filament connected to the metal pipe at a central portion. The columnar chip of the hexaboride single crystal is formed into a cone shape at a portion closer to a tip than a portion held in the metal pipe, and a tip end portion having the cone shape has a (310) crystal face. Schottky electrons are emitted from the (310) crystal face. According to the invention, it is possible to provide a novel electron source having monochromaticity, long-term stability of an emitter current, and high current density.