# Presentation: 427505

## Focusing X-rays to 1 nm –	Requirements and Approaches

- Jörg Maser
- Center for Nanoscale Materials
- X-ray Science Division
- NSLS II Workshop on Stability
- Apr. 19, 2007

## Outline

- Overall Considerations and Parameters
- Critical Specifications for Nanofocusing
- Technical Approach to Instrument design
- Short notes on Optics:

## I) Overall considerations

- Goal: reach a spatial resolution of 1 nm
- Considerations:
- What optics (not discussed here)?
- How to measure?
- Requirements for positioning/stability
*Source*
*Beamline*
*Instrument*
- Assumptions:
- Optics exists (distinguish monolithic and non-monolithic optics)
- Diffraction-limited focusing required	 spatially coherent wavefront
- No full-field optics feasible  scanning  for DAQ required

## Typical nanofocusing parameters for NSLSII

- Overall parameters of an NSLSII Nanofocusing Beamline (5 m straight)
- Source distance: 				50 m
- Source size dv(FWHM)			3.8 um
- Lateral coherence length at position of focusing optics (sv=/):
- 							520 um, E = 10 keV
- Focal length:				4.2 mm, E = 10 keV
- Depth of focus:				DOF = 20 nm

- Source

- Focusing Optics, Specimen

## II) Source stability, size/position

- Size of *measured *focal spot:  =  ( [DL2 +  (Mv)2 + M source2 ]+ BL2+ instrument2)
- M: Source magnification; : stability of subsystems
- Example:
- Multilayer Laue Lens as focusing optics:
- drN = 0.9 nm
- Mv = 0.28 nm, M = 710-5, M  spatial coherence criterion (1/2, 1/)
- source = 0.1 = 0.16 m, Msource = 0.01 nm
*Total size of focal spot: 0.94 nm (before beamline/instrument stability)*

******a**

*********dl******  ~  ************/sin ************a ******~ dr******N***

- spatially coherent wavefront

## Source stability, angle

- Coherent angle @ 10 keV:
-  = 310-5 rad
- 	SR angle = 2/(N) = 1.410-5 rad
- 	source divergence, v: ******y****’**
- No overfilling in vertical direction; angular fluctuations will directly lead to intensity variations
- ’source = 0.1y’: 		I/I = 0.5%.
- Required stability _experiment-dependent_
*Spectroscopy, dichroism experiments very sensitive*
*Sufficient for fluorescence imaging*
***I could be addressed by XBPM in beamline*

## II) Critical Specifications for Nanofocusing – 				Overall considerations

- How to measure?
- Assume we have a suitable specimen
*	**<< 1 nm features, thickness ~20 nm (t < DOF)*
- Assume we have an optimized detector/electronics
***sr *detection, 50% efficiency, high count rate capability: > 106 Hz
- 	      *** * 1 msec data acquisition time (based on CNM NPI simulations)
- Assume 100 pixels for scans
- Positioning requirement:
- Require mechanical positioning of specimen/object of < 0.5 nm
- Drift requirement:
- Assume: B = 11021 Ph/s/mr2/mm2/0.1%BW
- Line scan: require 1 pixel shift per scan line 	*** * drifts < 4 nm/s
- 2D scan: Require 10 pixel shift per line	 *** * drifts < 4 Å/s

## X-ray Fluorescence Imaging (Stefan Vogt, unpublished)

- Fig. 2.5: Simulation of fluorescence imaging of 5 nm thick test objects of Ti, Cu and W nanoparticles. The diameter of the test objects is 5 nm and 20 nm, respectively. An excitation energy of 12.2 keV is used.
- Fig. 2.5A and 2.5 B are for an exposure time of 15 msec. A solid angle acceptance of  sr and a detector efficiency of 50% is assumed. The same simulation is shown  in linear scale and log scale.
- Fig. 2.5 C shows the same object for an exposure time of 1.5 seconds (log scale). The position of individual nanoparticles of 5 nm diameters is indicated by blue arrows.

- B)

- C)

- A)

- From CNM Nanoprobe Instrument PDR, June, 2005

- Assumed:
- B = 51019 Ph/s/mr2/mm2/.1%BW
- Coherent Flux:
- Fcoh= 5109 Photons/s @ 12.2 keV

## Consideration for beamline design

- Nonsymmetric source size
- Astigmatic beamline design required
- Spatial filter  remove source/BL optics motion effects
- High position accuracy requirements for beam defining aperture

- BDA

- Optical Design
- CNM Nanoprobe Beamline

- Monochromator

## Critical Components and relevant positioning specifications

- Lateral stability requirement: 	<< 1 nm
- Longitudinal requirement: 	<< 20 nm
- Monochromator angular stability (1st vs 2nd crystal):
- 				 << 0.1 ****rad, DCM at 25 m
- Stability source vs instrument: 	<<  3.8 um

- Instrument

-  << 1 nm

-  << 20 nm

-  << 10-7 rad

-  < 1.9 um

- Source

- Monochromator

## Other considerations

- Required Thermal stability
- Typical overall dimensions of optics/specimen assembly: 100 mm
- Invar: 		 = 1.610-6 m/m/K
*** **expansion of 160 nm/K **	**** **	****T < 2.5****10**-3** K*
- However: significant are only *differential *drifts
*Design using proper geometry can significantly reduce need for temperature stabilization*
- Tradeoff between temperature stability and air flow/acoustically excited vibrations

## III) Technical approach to instrument design:

- Overall considerations:
- Amplitude of floor vibration: 20 – 30 nm
- Provide nanometer positioning accuracy
- Stiff design: Aim at in-phase “vibration” of sample and optics
- Use of similar components/geometries for “stacks” of positioners
- Position encoding and feedback
- Conceptual Challenge:
- Position sensors cannot be placed close to specimen/zone plate. Typical distance: 10 – 20 mm
- 	 careful engineering of optics/specimen support

- Sample

- EDS

## CNM Hard X-ray Nanoprobe Beamline at the Advanced Photon Source, 26-ID 

- Hard X-ray Nanoprobe Beamline

- Nanoprobe Instrument

## Hard X-ray Nanoprobe Instrument

***Hard X-ray Nanoprobe Instrument***

- Zone plate

- Sample

- CNM/APS design; XRADIA TXM + engineering

- Flexure-based fine scanning stage

- Zone plate and specimen Module

**X-rays**

## Some considerations on focusing optics

- Desired: Monolithic Optics
- _Realistic_ 1 nm optics: non-monolithic approach might be necessary
- e.g. 2-components optics: 12 degrees of freedom

**Ideal Volume Optics**

**Currently fabricated at ANL**

- 2D MLL

## Summary

- Source stability requirements – specifications sufficient for nonofocusing using fluorescence detection
- Position stability:			0.1y
- Source size stability			0.1y
- Beamline stability
- Monochromator:   << 0.1 ****rad
- Beamline apertures (e.g. h:  << 20 um). Heatload issues to be considererd
- Instrument/source motion: < 
- Instrument design/stability
- Instrument to source: 	
- Optics/specimen stability: 	 << 1 nm (lateral),  < 20 nm (longitudinal)