Nitrogen-Doped Ultrananocrystalline Diamond Field Emitters
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Solution Overview
Problem
Conventional electron emitters, including field emitters and photocathodes, face challenges such as complexity in scaling, mechanical and electrical strength requirements, low turn-on electric fields, and instability in varying vacuum conditions, limiting their applicability in industrial applications like electron-linear accelerators and synchrotron sources.
Innovation Solution
The development of nitrogen-doped ultrananocrystalline diamond (N-UNCD) based field emitters and hydrogen-terminated N-UNCD (N-UNCD:H) based photocathodes, which are operable at moderate vacuum pressures up to 10^-5 Torr, offering enhanced stability and efficiency by eliminating the need for complex lithography and transfer steps, and allowing mass production on metal substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional field emitters use micro- or nano-lithography and additional transfer steps for fabrication, then emitting tip precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces conventional micro- or nano-lithography mechanical fabrication processes with a chemical vapor deposition (CVD) process that directly grows diamond nanotips on the substrate. This substitution eliminates complex lithography steps, pattern transfer, and alignment procedures, significantly reducing device complexity while maintaining manufacturing precision through controlled chemical deposition
Solution Approach 2:
The patent changes the fabrication approach from top-down lithographic patterning to bottom-up CVD growth. By controlling parameters such as methane flow rate, hydrogen plasma power, substrate temperature, and deposition time, the process directly forms nanotips with precise dimensions and controlled nitrogen doping concentrations, achieving both precision and simplicity
2Use of energy by moving object
If alkali based photocathodes are used to achieve high efficiency, then quantum efficiency is improved, but stability against vacuum and air exposure deteriorates
Solution Approach 1:
The patent creates a composite structure by incorporating nitrogen-doped diamond material with specific electronic properties into the photocathode system. The nitrogen doping introduces electronic states that enable high quantum efficiency comparable to alkali photocathodes, while the diamond matrix provides inherent chemical stability and resistance to vacuum and air exposure, eliminating the need for ultrahigh vacuum operation
Solution Approach 2:
The patent changes the material composition parameter by introducing nitrogen dopants at controlled concentrations (0.05-0.5 atom %) into the ultrananocrystalline diamond structure. This parameter change modifies the electronic band structure to enable efficient photoemission while maintaining the material's intrinsic stability, allowing operation at moderate vacuum pressures up to 10^-5 Torr
3Power
If field emitters are scaled to tens or hundreds of millimeters, then beam power capability is improved, but fabrication complexity increases
Solution Approach 1:
The CVD fabrication process is universally applicable to substrates of various sizes, shapes, and curvatures. The same deposition conditions that produce precise nanotips on small substrates can be scaled to produce uniformly distributed emitters across large-area substrates, enabling fabrication of millimeter-scale field emitter arrays with high beam power capability without increasing fabrication complexity
Solution Approach 2:
The patent uses a segmented approach where the large-area substrate is covered with a uniform layer of nanodiamond seeds, which then serve as nucleation sites for CVD growth. This segmentation allows parallel growth of numerous nanotips across the entire substrate area, enabling scaling to large dimensions while maintaining simple, uniform fabrication processes
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
These N-UNCD and N-UNCD:H emitters provide robust, efficient, and scalable electron sources with higher emitting sites and quantum efficiency, maintaining stability in air and moderate vacuum conditions, suitable for diverse applications including electron accelerators and synchrotron sources.
Implementation Method 1
Field emitters are devices that produce electrons under the influence of an electric field
Implementation Method 2
photocathodes are electron emitters that emit electrons when exposed to photons due to photoelectric effect
Implementation Method 3
The first layer is exposed to a microwave plasma to form a N-UNCD film on the first layer
Data Source
AI summary
A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 1012 to about 1014 emitting sites per cm2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.