# Presentation: 521820

## 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:
-  It can be done; there is no physical reason we cannot get to 1nm
-  However, it will take resources and a targeted effort.

**Notes:**
Soft x-rays are bottoming out. Hard xrays would bottom out here. 

## Basic Issues

- Metrics
- Numerical Aperture and resolution
- Depth of field
- Aperture
- Efficiency
- Chromaticity
- Modulation Transfer Function

- If resolution is 1nm
- => then DOF =27nm

## 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 |

##  Paths to 1nm 

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

## 1.Single Bounce Solid Metal Mirrors 

| 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

- Single Bounce Solid Metal Mirrors: Best case is for the most dense material Pt.

- * Multiple bounce mirrors can improve the situation.

## 2.Binary Zone Plates

- Equation for fresnel boundaries

- 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

## 3.Refractive

- 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!

- Courtesy of Schroer

##  Paths to 1nm 

| Optic Type | Comment |
| --- | --- |
| 1. Single bounce Solid Metal Mirrors | X |
| 2. Binary Zone Plates | X |
| 3. Solid Refractive lenses | X |
| 4. Multilayer Mirrors | Pursued by ESRF,Spring8 |
| 5. Multilayer Lens | Proposed NSLS-II R&D |
| 6. Kinoform | Proposed NSLS-II R&D |

## 4. Multilayer Mirror (MLM)

**O. Hignette   Optics group- ESRF **

- Approach being followed by ESRF and Spring8

- 45nm ESRF

## 5. Novel Approach : Multilayer Laue Lenses 

- substrate

- Varied line-spacing grating

- Depth-graded multilayers on flat Si substrate

- Multilayer Linear Zone Plate

-  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)

**Crossed Linear Zone Plate : 1-D focusing optics**

- Deposition + Sectioning + Assembling

- From CNM,APS group

## Fabrication of MLL

- Growth

- Si substrate

- Dicing ~ 1mm

- Polishing ~ 5-25 m

- Assembling by face to face lens configuration

- Central stop

- Tilting

**WSi****2****/Si, 12.4 ********m**

******r~58 nm**

******r~10 nm**

## Measured Focal Spot @ 19.5 keV X-rays

*Incident beam size : 12.4 ****m (H) X 50 ****m (V)*

*Focal spot size : ****~ 30**** nm (H)*

***Focal spot***

***Incident beam***

**FWHM****  ****:**** **
**72.7 nm (sample A)**
**57.4 nm (sample B)**
**30.6 nm (sample C)**

- Sample C,* ****r**out* =10 nm

- Latest unpublished ~ 19nm

## MLL issues

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

## Why we need “wedges”

## 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.

**Notes:**
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.

## Single Crystal MLL Issues

| 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)

- Use of single crystal lattice would raise some issues. We have carried out some initial simulations to gain some insight into these:

## 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

## 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

## 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.

## Summary of the Kinoform Case 

- 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.

- Summary of the Kinoform Case

## Multiple kinoform lenses can go beyond critical  angle limit

**Multiple kinoform lenses can go beyond critical  angle limit**

- 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.

- 2C

## 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)

## 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 |

## Other Components of Proposed R&D plan

- MLL 
- Kinoform 
- Measurements and metrology
- Simulations/theory/Computational

- Benefits all optics

## Testing and Metrics

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

## 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.

## Can crossed optics get down to 1nm?

- showing the replacement of the spherical wave by a pair of orthogonal parabolic terms.

- For 100 micron aperture, focal length 1cm, we can use crossed lenses down to at least 10nm, but how far can we go?

- Using the Fresnel Kirchhoff Integral

- Limit of the approximation:

## 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

## 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