Planar field emitters and high efficiency photocathodes based on ultrananocrystalline diamond
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 10 12 to about 10 14 emitting sites per cm 2 . 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.
1. A method of forming a field emitter, comprising:
disposing a first layer on a substrate;
seeding the first layer with nanodiamond particles;
maintaining the substrate with the seeded first layer disposed thereon at a first temperature and a first pressure in a mixture of gases, the mixture including nitrogen; and
exposing the first layer to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, the nitrogen doped ultrananocrystalline diamond film having a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %,
wherein, the field emitter has about 10 12 to about 10 14 emitting sites per cm 2 .
2. The method of claim 1 , wherein the first layer includes a transition metal.
3. The method of claim 2 , wherein the first layer includes at least one of molybdenum and niobium.
4. The method of claim 1 , wherein the first temperature is in the range of about 650 degrees Celsius to about 950 degrees Celsius.
5. The method of claim 1 , wherein the first pressure is in the range of about 40 Torr to about 70 Torr.
6. The method of claim 1 , wherein the substrate is at least one of planar, microstructured and nanostructured.
7. The method of claim 5 , wherein the substrate includes stainless steel.
8. The method of claim 5 , wherein the substrate is planar and wherein the nitrogen doped ultrananocrystalline diamond film has a current density in the range of about 0.1 mAmp/cm 2 to about at least 25 mAmp/cm 2 between an electric field gradient of about 45 MV/m to about 65 MV/m, respectively.
9. The method of claim 1 , wherein the nitrogen doped ultrananocrystalline diamond film has a beam emittance in the range of about 0.5 mm×mrad/mm-rms to about 3 mm×mrad/mm-rms at 65 MV/m.
10. The method of claim 1 , wherein the nitrogen doped ultrananocrystalline diamond film has a full width half maximum longitudinal energy spread of about 0.5% to about 1%.
11. A method of forming a photocathode, comprising:
disposing a first layer on a substrate;
seeding the first layer with nanodiamond particles;
maintaining the substrate with the seeded first layer disposed thereon at a first temperature and a first pressure in a mixture of gases, the mixture including nitrogen;
exposing the first layer to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, the nitrogen doped ultrananocrystalline diamond film having a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %;
maintaining the nitrogen doped ultrananocrystalline diamond film at a second temperature and second pressure in hydrogen gas; and
exposing the nitrogen doped ultrananocrystalline diamond film to a microwave plasma to hydrogen terminate the nitrogen doped ultrananocrystalline diamond film.
12. The method of claim 11 , wherein the first layer includes a transition metal.
13. The method of claim 11 , wherein the first temperature is in the range of about 650 degrees Celsius to about 950 degrees Celsius.
14. The method of claim 11 , wherein the first pressure is in the range of about 40 Torr to about 70 Torr.
15. The method of claim 11 , wherein the substrate is stainless steel.
16. The method of claim 11 , wherein the hydrogen terminated nitrogen doped ultrananocrystalline diamond film has a quantum efficiency of at least 5×10 −8 electrons/photons between a visible wavelength range of about 405 nm to about 436 nm, respectively.
17. The method of claim 11 , wherein the hydrogen terminated nitrogen doped ultrananocrystalline diamond film has a quantum efficiency of at least 10 −3 electrons/photons at wavelengths in the range of about 240 nm to about 270 nm.
18. The method of claim 11 , further comprising:
operating the photocathode until a performance of the photocathode is depleted; and
exposing the photocathode to an hydrogen plasma to restore the performance of the photocathode.
19. A field emitter, comprising:
a planar substrate;
a first layer disposed on the planar substrate; and
a nitrogen doped ultrananocrystalline diamond film disposed on the first layer, the nitrogen doped ultrananocrystalline diamond film having a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %,
wherein, the field emitter has about 10 12 to about 10 14 emitting sites per cm 2 .
20. The field emitter of claim 19 , wherein the nitrogen doped ultrananocrystalline diamond film has a current density in the range of about 0.3 mAmp/cm 2 to about 25 mAmp/cm 2 at an electric field gradient of about 45 MV/m to about 65 MV/m, respectively.
21. The field emitter of claim 19 , wherein the nitrogen doped ultrananocrystalline diamond film has a beam emittance in the range of about 0.5 mm×mrad/mm-rms to about 3 mm×mrad/mm-rms.
22. The field emitter of claim 19 , wherein the nitrogen doped ultrananocrystalline diamond film has a full width half maximum longitudinal energy spread of about 0.5% to about 1%.
23. The field emitter of claim 19 , wherein the field emitter is operable via a radio frequency energy source.
24. The field emitter of claim 19 , wherein the planar substrate is formed from stainless steel.
25. A photocathode, comprising:
a substrate;
a first layer disposed on the substrate; and
a hydrogen terminated nitrogen doped ultrananocrystalline diamond film disposed on the first layer, the hydrogen terminated nitrogen doped ultrananocrystalline diamond film having a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %,
wherein, the photocathode has about 10 12 to about 10 14 emitting sites per cm 2 .
26. The photocathode of claim 25 , wherein the hydrogen terminated nitrogen doped ultrananocrystalline diamond film has a quantum efficiency in the range of about 5×10 −8 electrons/photons to about 5×10 −9 electrons/photons between a visible wavelength range of about 405 nm to about 436 nm, respectively.
27. The photocathode of claim 26 , wherein the hydrogen terminated nitrogen doped ultrananocrystalline diamond film has a quantum efficiency of about 10 −3 electrons/photons at wavelengths in the range of about 240 nm to about 270 nm.
28. The photocathode of claim 26 , wherein the photocathode is operable at a pressure of up to about 10 −5 Torr.
29. The photocathode of claim 26 , wherein the nitrogen doped ultrananocrystalline diamond film is terminated with deuterium.