High aspect-ratio X-ray diffractive structure stabilization methods and systems
A method to stabilize planar nanostructures, for example grating and zone plate lenses that are typically used for directing or focusing x-ray radiation, includes the deposition of a top, stabilizing layer. The structures are typically made on a flat substrate, and therefore are only fixed at the bottom. At high aspect ratio, the stability can be poor since small forces such as electrostatic forces and van de Waals forces that are often present can alter the structure. The top coating of a metallic material such as titanium constrains the nanostructures at the top and at the same time eliminates electrostatic forces and reduces any thermal gradient that may be present across the device.
1. A diffractive x-ray optic, comprising:
a substrate;
a diffractive layer of zone structures spaced apart at varying distances from one another and disposed and connected only along a bottom surface to the substrate, said zone structures having aspect ratios of 3-100 and varying zone widths including 15-100 nm; and
a first top layer, to prevent tilting of the zone structures, disposed along and adjacent to opposite top surfaces of the diffractive layer of zone structures from the substrate, the first top layer spaced away from the substrate and bridging over gaps between at least some of zone structures along a height of the diffractive layer zone structures.
2. An optic as claimed in claim 1 , wherein the structures form a periodic grating diffractive optic.
3. An optic as claimed in claim 1 , wherein the structures form a zone plate lens diffractive optic.
4. An optic as claimed in claim 1 , wherein the diffractive layer comprises gold.
5. An optic as claimed in claim 1 , wherein the diffractive layer comprises tungsten.
6. An optic as claimed in claim 1 , wherein the diffractive layer comprises silicon.
7. An optic as claimed in claim 1 , wherein the first top layer comprises titanium.
8. An optic as claimed in claim 1 , wherein the first top layer comprises molybdenum.
9. An optic as claimed in claim 1 , wherein the first top layer comprises aluminum.
10. An optic as claimed in claim 1 , wherein the first top layer has a thickness of 50-500 nm.
11. An optic as claimed in claim 1 , wherein the first top layer creates voids defined in a lateral direction between the structures and defined in a vertical direction between the top layer and the substrate.
12. An optic as claimed in claim 1 , further comprising a second top layer disposed onto the first top layer to seal a zone plate of the diffractive zone structures, wherein tops of the diffractive zone structures are secured and bridged over the gaps by said first and second top layers, and bottoms of the diffractive zone structures are secured to said substrate.
13. A method for fabricating a diffractive x-ray optic, the method comprising:
on a substrate, forming a diffractive layer of zone structures spaced apart at varying distances from one another and disposed and connected only along a bottom surface to the substrate, said zone structures having aspect ratios of 3-100 and varying zone widths including 15-100 nm; and
depositing a first top layer, to prevent tilting of the zone structures, disposed along and adjacent to opposite top surfaces of the diffractive layer of zone structures from the substrate, the first top layer spaced away from the substrate and bridging over gaps between at least some of zone structures along a height of the diffractive layer zone structures.
14. A method as claimed in claim 13 , wherein the step of forming the diffractive layer comprises forming the structures into a periodic grating.
15. A method as claimed in claim 13 , wherein the step of forming the diffractive layer comprises forming the structures into a zone plate lens.
16. A method as claimed in claim 13 , wherein the diffractive layer comprises gold.
17. A method as claimed in claim 13 , wherein the diffractive layer comprises tungsten.
18. A method as claimed in claim 13 , wherein the diffractive layer comprises silicon.
19. A method as claimed in claim 13 , wherein the first top layer comprises titanium.
20. A method as claimed in claim 13 , wherein the first top layer comprises molybdenum.
21. A method as claimed in claim 13 , wherein the first top layer comprises aluminum.
22. A method as claimed in claim 13 , wherein the first top layer has a thickness of 50-500 nm.
23. A method as claimed in claim 13 , wherein step of depositing the first top layer comprises depositing at least part of the top layer at an angle of 30-75 degrees to a plane of the substrate.
24. A method as claimed in claim 23 , wherein step of depositing the top layer further comprises depositing part of the first top layer at an angle about normal to the plane of the substrate.
25. A method as claimed in claim 13 , wherein step of depositing the first top layer comprises depositing at least part of the top layer at an angle about normal to the plane of the substrate.
26. A method as claimed in claim 13 , wherein the first top layer creates voids defined in a lateral direction between the structures and defined in a vertical direction between the top layer and the substrate.
27. An method as claimed in claim 13 , further comprising depositing a second top layer disposed onto the first top layer to seal a zone plate of the diffractive zone structures, wherein tops of the diffractive zone structures are secured and bridged over the gaps by said first and second top layers, and bottoms of the diffractive zone structures are secured to said substrate.