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1nm R&D plan

1nm R&D plan. K. Evans-Lutterodt Contributions from: C. Jacobsen, N. Bozovic, I. Bozovic, J.Maser, A.Snigirev, C. Schroer, O.Hignette, and many others. Current Trends in X-ray optics. Points courtesy of C. Jacobsen. Bottom Line:

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1nm R&D plan

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  1. 1nm R&D plan K. Evans-Lutterodt Contributions from: C. Jacobsen, N. Bozovic, I. Bozovic, J.Maser, A.Snigirev, C. Schroer, O.Hignette, and many others

  2. Current Trends in X-ray optics Points courtesy of C. Jacobsen • Bottom Line: • It can be done; there is no physical reason we cannot get to 1nm • However, it will take resources and a targeted effort.

  3. Basic Issues • Metrics • Numerical Aperture and resolution • Depth of field • Aperture • Efficiency • Chromaticity • Modulation Transfer Function If resolution is 1nm => then DOF =27nm

  4. Implications of Goals/Source Demagnification Spot Size Diffraction limit Focal Length • NSLS2 has a 6μm x 39μm source size in low  straight. • If resolution is 1nm, and =0.1nm, => NA = 0.1

  5. Paths to 1nm

  6. 1.Single Bounce Solid Metal Mirrors Single Bounce Solid Metal Mirrors: Best case is for the most dense material Pt. Table courtesy of O.Hignette * Multiple bounce mirrors can improve the situation.

  7. 2.Binary Zone Plates • The spot size is of order the smallest zone • Work at harmonics, reduces efficiency • As photon energy increases, the zone plate thickness T increases • To get smallest spot sizes at hard x-ray energies requires • Large aspect ratios that are difficult to manufacture • E-beam lithography tools have tolerances of order 2nm Equation for fresnel boundaries

  8. 3.Refractive Lens Transmission Solid Refractive Lens Effective Lens Aperture Optic Axis Courtesy of Schroer • 1. Absorption Incident Beam t=y2/(2F) Transmission ~ exp( -4t/) Resolution ~ 1/f To get 1nm , we can have f = 1μm, aperture 100nm ! Aperture too small!

  9. Paths to 1nm

  10. 4. Multilayer Mirror (MLM) •  d-spacing • Wavelength f focal length L mirror length NA numerical aperture diffraction limited full width half maximum O. Hignette Optics group- ESRF 45nm ESRF Approach being followed by ESRF and Spring8

  11. 5. Novel Approach : Multilayer Laue Lenses Crossed Linear Zone Plate : 1-D focusing optics From CNM,APS group Deposition + Sectioning + Assembling Multilayer Linear Zone Plate Varied line-spacing grating • Deposit varied line-spacing grating on flat substrate (thinnest structures first!) • Section to 5-20 m thickness (high aspect ratio structure) • Assemble into a multilayer linear zone plate (MLZP) • Assemble two MLZP’s into a single device (MLL) substrate Depth-graded multilayers on flat Si substrate

  12. Fabrication of MLL Dicing ~ 1mm Polishing ~ 5-25 mm Growth Si substrate Dr~58 nm Assembling by face to face lens configuration WSi2/Si, 12.4 mm Central stop Dr~10 nm Tilting

  13. Measured Focal Spot @ 19.5 keV X-rays Sample C,Drout =10 nm Focal spot Incident beam FWHM: 72.7 nm (sample A) 57.4 nm (sample B) 30.6 nm (sample C) Focal spot size : ~ 30 nm (H) Incident beam size : 12.4 mm (H) X 50 mm (V) Latest unpublished ~ 19nm

  14. MLL issues Need to fabricate wedged MLL to get below 5nm Wedged deposition is novel technology. Works better at higher energies > 20keV Metrology?

  15. Why we need “wedges”

  16. Our Proposed MLL approach • 1. Use single crystal lattice matched oxides that can be grown atomically smooth.   • 2. High density (BaBiO3) and low density films (MgO) with z lattice spacings 0.42 and 0.43 respectively. • 3. Bozovic will be a resource for the growth effort.

  17. Single Crystal MLL Issues Use of single crystal lattice would raise some issues. We have carried out some initial simulations to gain some insight into these: (N.Bozovic NSLS-II)

  18. Timelines for MLL • FY07 • Explore materials for single crystal MLL approach. • Explore techniques to deposit multi-layers in wedged MLL geometry. • Carry out coupled wave (vector) calculations of MLL to determine sensitivity to errors. • Develop positioning techniques to mount and manipulate up to 4 MLL sections • FY08 • Develop techniques to deposit multi-layers for wedge MLL geometry • Develop metrology capable of determining zone width and placement to ~2nm resolution. • Develop techniques to slice an MLL section from graded multilayer • FY09 • Design a prototype MLL device (optics and mechanics) with 2nm limit • FY10 • Construct 2nm prototype device

  19. Proposed Strategies for MLL • Initially grow flat MLL, but in parallel will design chambers for wedged growth (I. Bozovic). (Possibly adapt the KB mirror fabrication techniques from APS.) • Develop Metrology for layers

  20. 7.Kinoform Instead of solid refractive optic: Use a kinoform: • One can view the kinoform equivalently as • A blazed zone plate • An array of coherently interfering micro-lenses.

  21. Summary of the Kinoform Case a) F 2F b) Intensity c) N.A.= Mc M lenses Normalized focal length • Kinoform transmission function is almost uniform as a function of lens aperture, and so • => NA of the lens is not limited by absorption. • 2. Kinoform does not have to be fabricated with structures as small as the resolution of the lens. • 3. A compound lens gets around the small , which limits the focusing power of a single lens, and would otherwise limit the spatial resolution to 0.61/c.

  22. Multiple kinoform lenses can go beyond critical angle limit 2C D • Single refractive lens has deflection angle D= C, => resolution limit is /C • We have fabricated a 4 lens compound lens with f =25mm, total aperture =0.3mm, D= 2C • Imperfect lens: Actual result for lens array is 1.1 C . Need to improve fabrication.

  23. Kinoform issues • While Kinoform is further behind at present (600nm at NSLS), no new technology is needed. Investments here have been small to date. • We need to improve etch quality • Etch depth is 100μm; need to improve. • Reduce roughness of etched sidewall • Test lens designs for n>4. (n=24 needed for Si)

  24. Timelines for Kinoform

  25. Other Components of Proposed R&D plan • MLL  • Kinoform  • Measurements and metrology • Simulations/theory/Computational Benefits all optics

  26. Testing and Metrics • Need to develop testing facilities. • Diagnostics at NSLS • Diagnostics at APS • Numerical support, and investigation of new methods (Souvorov)

  27. Computational Research • Going beyond Fresnel Kirchhoff thin lens approximation • Develop a simulation code that one can drop in density matrices representing real optics. • Help in diagnostics simulations.

  28. Can crossed optics get down to 1nm? Using the Fresnel Kirchhoff Integral showing the replacement of the spherical wave by a pair of orthogonal parabolic terms. Limit of the approximation: For 100 micron aperture, focal length 1cm, we can use crossed lenses down to at least 10nm, but how far can we go?

  29. Can crossed optics get down to 1nm? Answer: Yes, but with increased background Small NA, crossed lens indistinguishable from two independent lenses Large NA ~0.1, crossed lens ok but: Central spot still sharp but weaker, More intensity outside the spot => Lower signal to noise ratio

  30. Summary • 1nm optics are possible, but will require a targeted R&D effort • NSLS-II is proposing to pursue 2 of the possible paths. • MLL: Develop wedged structures • Kinoforms: Improve etch quality and increase lens count

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