Field Emission Electron Source With Faceted (100) Tip for Stable Beam
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Solution Overview
Problem
Field emission electron sources using hexaboride or transition metal carbide single crystals face issues with low radiation angle current density and current stability due to electron emission from planes other than the (100) plane, leading to electron beam stimulation desorption gas and reduced monochromaticity.
Innovation Solution
A first (100) plane top facet is formed at the tip of the crystal, surrounded by {n11} and {n10} side facets, with a microcrystal (100) plane top facet on the first (100) plane, optimizing the electron emission surface to enhance stability and reduce unwanted emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a hexaboride or transition metal carbide single crystal is used as the field emission electron source, then the work function is lower than W and electrons can be transmitted by a lower electric field, but the radiation angle current density is low and current stability deteriorates due to electron emission from planes other than the (100) plane
Solution Approach 1:
The patent applies local quality by creating a specific facet structure where only the (100) plane is exposed at the tip surface. The crystal is oriented along the <100> direction and processed to form a dominant (100) facet, ensuring that electron emission occurs exclusively from this plane with the desired low work function, while side facets are configured to suppress emission from other planes.
Solution Approach 2:
The patent employs asymmetry by designing an unequal facet structure where the (100) top facet has a significantly larger area than the side facets. This asymmetric configuration ensures that the majority of electron emission comes from the (100) plane, while the smaller side facets contribute minimally, thus maintaining current stability.
2Illumination intensity
If the distal end of the crystal is sharpened to increase electron emission density, then luminance increases, but emission from multiple crystal planes occurs causing reduced monochromaticity
Solution Approach 1:
The patent ensures that only the (100) plane with optimal electron emission properties is exposed at the tip surface. By controlling the crystal orientation and facet geometry, the emission surface is localized to this specific crystal plane, maintaining both high luminance and monochromaticity.
Solution Approach 2:
The patent converts the potential harm of multi-plane emission into a benefit by using the side facets with higher work functions as emission-suppressing structures. These side facets, which could potentially emit electrons, are instead designed to redirect the electric field and suppress emission, thereby protecting the monochromaticity of the electron beam.
3Stability of the object's composition
If side facets with large area are used to stabilize the crystal structure, then structural stability improves, but electron emission from these facets increases reducing radiation angle current density ratio
Solution Approach 1:
The patent assigns different functional qualities to different facets: the (100) top facet is designed for electron emission with optimal work function, while the side facets are configured with geometries and orientations that suppress electron emission. This local differentiation allows the side facets to provide structural stability without compromising emission performance.
Solution Approach 2:
The patent creates an asymmetric facet configuration where the (100) top facet area is significantly larger than the side facet areas. This asymmetry ensures that even though side facets provide structural support, their contribution to electron emission is minimized, maintaining a high radiation angle current density ratio.
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 increases the radiation angle current density ratio and improves current stability, providing a stable electron beam for high-resolution applications.
Implementation Method 1
By concentrating an external electric field F at the distal end of the W tip, a high electric field is applied, and electrons e at the W tip are quantum mechanically transmitted through an energy barrier that is effectively thinned and are emitted into vacuum.
Implementation Method 2
By concentrating an external electric field F at the distal end of the W tip, a high electric field is applied
Data Source
AI summary
A field emission electron source using a plane of a hexaboride single crystal or a transition metal carbide single crystal as an electron emission surface, to improve a ratio of a radiation angle current density to a total current and improve current stability. A first plane top facet is formed at a distal end of a tip of a hexaboride single crystal or a transition metal carbide single crystal with a <100> axis, the first plane top facet is surrounded by side facets that include at least four {n11} planes and at least four {n10} planes, and of which a total area of {n11} plane side facets is larger than a total area of {n10} plane side facets, and a microcrystal having a second plane top facet is formed on a plane of the first plane top facet, and electrons are mainly from the second plane top facet.