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
Soft x-rays are bottoming out. Hard xrays would bottom out here.
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
Efficiency
Chromaticity
Modulation Transfer Function
If resolution is 1nm
=> then DOF =27nm

4. Implications of Goals/Source
NSLS2 has a 6μm x 39μm source size in low  straight.
If resolution is 1nm, and =0.1nm, => NA = 0.1
F(mm)
Aperture
Image Size 1
100μm
0.72x1.1nm 10
1mm
1.3x8nm
100
10mm
12x80nm
Focal Length
Spot Size
Diffraction limit
Demagnification

5. Paths to 1nm Optic Type Comment X 1. Single bounce Solid Metal Mirrors
2. Solid Refractive lenses
3. Binary Zone Plates
4. Multilayer Mirrors
5. Multilayer Lens
6. Kinoform

6. 1.Single Bounce Solid Metal Mirrors
Single Bounce Solid Metal Mirrors: Best case is for the most dense material Pt.
Technology
Theoretical limits
Spot size (FWHM)
Experimental spot sizes
FWHM (nm)
Facility
Fixed profile mirrors
Metal coating
25 nm 15keV
SP8 (1Km BL)
68X80 nm (white)
APS (BL34)
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 1. Absorption Incident Beam Lens Transmission
Courtesy of Schroer
1. Absorption
Lens Transmission
Effective
Lens
Aperture
Solid Refractive Lens
Optic Axis
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 Optic Type Comment X Pursued by ESRF,Spring8
1. Single bounce Solid Metal Mirrors X
2. Binary Zone Plates
3. Solid Refractive lenses
4. Multilayer Mirrors
Pursued by ESRF,Spring8
5. Multilayer Lens
Proposed NSLS-II R&D
6. Kinoform

10. 4. Multilayer Mirror (MLM)
O. Hignette Optics group- ESRF
diffraction limited
full width half maximum
 d-spacing
Wavelength
f focal length
L mirror length
NA numerical aperture
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 Si substrate Growth Dicing ~ 1mm
Polishing ~ 5-25 mm
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)
Incident beam size : 12.4 mm (H) X 50 mm (V)
Focal spot size : ~ 30 nm (H)
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.
Our proposal is to grow MLL from single xtal oxide thin films that can be grown atomically flat.
I Bozovic is a world expert n such films.

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:
Discrete Lattice
OK; like interface roughness
Density contrast
OK; larger contrast is better
Interfacial roughness
OK; reduced intensity into spot
Growth rate errors
Very important
Apodization
OK.
(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
Normalized focal length
Intensity c) b) a) 2F F
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.
N.A.= Mc
M lenses

22. Multiple kinoform lenses can go beyond critical angle limit
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
T=6m
Develop Deep Vertical Si etching
T=12m
Optimized E-beam Si process to allow many lens writes
Develop Etches for InSb, C, Si.
Test Compound Si lens sub 40nm
T=18m
Develop E-beam for alternate materials
T=24m
Test Alternate materials lens in xray
Test sub 20nm lens in xray
T=36m
Test sub 10nm lens

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