Truncated Cone Cathode Manufacturing for Uniform Electron Emission
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Solution Overview
Problem
Existing methods for manufacturing electron sources with truncated cone-shaped cathodes face challenges in achieving a balance between efficiently forming an electron emission surface with a reduced scar layer in a short time, improving current emission distribution uniformity, and increasing emission current density, due to limitations in processing speed and surface curvature issues.
Innovation Solution
A method involving forming the cathode tip into a truncated cone by machining, followed by focused ion beam processing to remove the surface layer, and using vapor phase etching or electrolytic polishing to remove processing scars, allowing for a flattened surface with reduced sagging and improved uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical polishing is used to form a truncated cone shape, then the electron emission area is enlarged and operation at high angular current density becomes possible, but the emission current density becomes uneven due to processing surface scars
Solution Approach 1:
The patent replaces mechanical polishing with ion beam processing to form the truncated cone shape and remove surface scars. The ion beam processing eliminates the mechanical contact that causes surface scars, thereby achieving uniform emission current density while maintaining the ability to operate at high angular current densities.
Solution Approach 2:
The patent introduces ion beam processing as an intermediary step between mechanical shaping and final electron emission. This intermediary process removes the harmful surface scars created by mechanical polishing without altering the overall truncated cone geometry, thus resolving the contradiction between productivity and manufacturing precision.
2Manufacturing precision
If focused ion beam processing is used to remove processing scar layer, then emission current density uniformity is improved, but processing time increases significantly
Solution Approach 1:
The patent divides the surface treatment process into two distinct stages: first, mechanical polishing to rapidly remove the bulk of the surface layer and form the basic shape; second, ion beam processing to selectively remove the remaining scar layer and achieve uniform emission. This segmentation allows each process to optimize for its specific function, reducing total processing time.
Solution Approach 2:
The patent applies mechanical polishing to remove more material than strictly necessary, creating an oversized truncated cone that is then refined by ion beam processing. This excessive initial removal by mechanical means compensates for the slow rate of ion beam processing, thereby reducing overall processing time while maintaining precision.
3Manufacturing precision
If electrolytic polishing is used to remove processing scars, then emission uniformity is improved, but the outer periphery of the emission surface sags and becomes curved
Solution Approach 1:
The patent replaces electrolytic polishing with ion beam processing to remove surface scars. The ion beam process removes material through physical sputtering rather than electrochemical dissolution, eliminating the sagging effect that occurs at the periphery during electrolytic polishing and maintaining surface flatness.
Solution Approach 2:
The patent changes the fundamental mechanism of surface treatment from electrochemical (electrolytic polishing) to physical (ion beam sputtering). This parameter change in the removal mechanism eliminates the differential removal rates that cause peripheral sagging, thereby maintaining both uniformity and flatness.
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 formation of an electron source with a uniform emission current density at high angular current densities, maintaining surface flatness and reducing scar layers, thus achieving a good balance among conflicting technical demands.
Implementation Method 1
a step of removing a surface layer of the flattened top surface by focused ion beam processing
Implementation Method 2
a step of removing a processing scar layer on the surface of the tip portion by means of vapor phase etching
Implementation Method 3
a step of removing a processing scar layer on the surface of the tip portion by means of vapor phase etching or electrolytic polishing
Implementation Method 4
This ZrO coating layer reduces the work function of the (100) plane of the tungsten monocrystals from 4.5 eV to about 2.8 eV, so that only the small crystalline facet corresponding to the (100) plane formed at the tip of this cathode forms an electron emission region
Data Source
Figure 1~2
Figure 3~4(b)
Figure 5~6
AI summary
An electron gun with a truncated-cone-shaped cathode with uniform emission current density is efficiently manufactured. A manufacturing method of a cathode electron gun equipped with a supply source for diffusing oxide of a metal element on a single crystal needle of tungsten or molybdenum includes steps of forming a truncated-cone-shape having a flat plane at a single crystal edge serving as the cathode by machining beforehand, thereafter thinning and removing a front layer of the flat plane by a focused gallium ion beam, and re-flattening it.