Multilayers in synchrotron optics Ch. Morawe, J-Ch. Peffen, K. - - PowerPoint PPT Presentation
Multilayers in synchrotron optics Ch. Morawe, J-Ch. Peffen, K. Friedrich, M. Osterhoff Outline Mirrors and multilayers Design and fabrication Performance and applications Summary and perspectives Ch. Morawe - ESRF Friday
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Basic geometry
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n2 < n1
Interaction of X rays with matter
Optical index Snell’s law Critical angle of total reflection In vacuum: Total reflection x-ray mirrors (TRM) But: @ E = 10 keV: Very long mirrors at high energies!
1 1 n i
1 2 2 1
cos cos n n
2 1
cos
C
n n 2
e C
E
5 0.3
C
mrad
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Total reflection mirror
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Single surface reflection Multiple reflections Multilayer
Recursive calculation of Fresnel coefficients and propagation
formalism (widely used in x-ray optics) Principle
fn-1,n : Fresnel coefficients En : Electric field at centre of layer n tn : Thickness of layer n
2 1 ,
r R
n R n n n n
E E a r
2 1 ,
2 2 2
cos n n t i n
n n
e a
1
, 1 1 , , 1 1 , 4 1 , 1 n n n n n n n n n n n
f r f r a r
Substrate
L.G. Parratt, Phys. Rev. 95, 359 (1954)
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Numerical simulation
Main features
Corrected Bragg equation
For θ >> θC
B A
sin 2 m
2 2 1 2 2
cos 2 n n m
ML reflectivity spectra
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X-ray reflectivity measurements and simulations
10-6 10
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10-3 10
10-1 100 0° 1° 2° 3° 4° 5° 6° Reflectivity
[Ir/Al2O3]10
Simulation of x-ray reflectivity
Vertical density profile
4 8 12 16 20 24 5 10 15 20 25 Mass density [g/cm
3]
Sample depth [nm]
[Ir/Al2O3]10 (Al
2
(Si) (Ir)
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Transmission electron microscopy (TEM)
Complementary to x-ray measurements !
[W/B4 C]50
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decreasing d-spacing increasing Bragg angle
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Reflecting multilayer
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Materials choice – Basic rules
1. Select low-Z spacer material with lowest absorption (βspacer ) 2. Select high-Z absorber material with highest reflectivity with spacer (δabs – δspacer ) 3. In case of multiple choices select high-Z material with lowest absorption (βabs ) 4. Make sure that both materials can form stable and sharp interfaces (lower d-spacing limit)
Computational search algorithms
(1988)
(1995)
Areas of application
(E = 280…550 eV)
X rays (E = 1…100 keV)
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Filling factor (Gamma ratio)
= tabs /Λ
tabs tspace
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Energy resolution of multilayers – Experimental results
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Reflective x-ray optics - Integrated reflectivity versus energy resolution
Integrated reflectivity
R(peak) = 100% Single Crystals Traditional ML's High-resolution ML's Depth-graded ML's
Be
110
Si
111
Ge
111
(Mirrors/Filters) forbidden area E = 8 keV 10-6 10-5 10-4 10-3 10-2 10-1 100 10-6 10-5 10-4 10-3 10-2 10-1 100
ESRF MLs
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Reflecting multilayer strong lateral thickness gradient
weak normal thickness gradient
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Lateral d-spacing gradient depending on surface curvature and beam divergence Shape Angle d-spacing including refraction correction (modified Bragg equation) Parabola Ellipse
sin p 2 f sin b pq sin s f
Flat Geometry
q p b
f s f p/2
2 2
cos 2 n m
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L m s m s m L
dx t x R f x x v x
Flux Speed Thickness
Substrate Mask Source
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Uniform coating area up to 1000mm x 150mm Loading bay Load lock Deposition zone Escape area Escape area
ESRF ML deposition facility Major upgrade in 2008
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Experimental results Specular reflectivity Thickness profile
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Fabrication history
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Multilayer high flux monochromators
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Total-reflection X-Ray Fluorescence (TXRF) for trace analysis (MEDEA)
C]40 and [Ir/Al2 O3 ]100
Atoms/cm2 (Ni)
2nd crystal (uncooled) Picomotor Copper plate Alignement system 1st crystal (cooled)
Beam in
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Old deposition system
[W/B4 C]40 : Λ = 4.0 nm Strong thickness decay (4% PV)
New deposition system
[W/B4 C]120 : Λ = 2.0 nm Residual d-spacing error <1% PV
Double [W/B4 C] ML monochromator for ID17 (Bio-Medical imaging)
100mm long and 150mm wide (each)
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Double ML monochromator for ID09B (Pump and probe)
after heat load chopper
C]40 and [Ir/Al2 O3 ]100 Pink beam Asymmetric spectrum @ 18 keV
0.3 s exposure
ML beam Symmetric spectrum with dE/E = 1.6% @ 25 keV)
3 s exposure Courtesy M. Wulff
Si powder
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White beam exposure (K. Friedrich)
beam
Surface figure
X-rays ML LN tank window Interferometer
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Kirkpatrick-Baez (KB) focusing devices
Albert V. Baez was the father of Joan Baez !
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Static KB mirrors
with MLs
Spring-8/Osaka University (Japan): Deterministic polishing
APS-ANL (USA): Profile coatings
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Dynamically bent KB mirrors at ESRF
Different configurations:
* O.Hignette et al., AIP Conf Proc. 879, 792 (2007) ID23 5 x 7 µm ID27 2 x 4 µm ID13 0.3 x 0.4 µm ID22NI 76 x 84 nm ID19 45 nm line focus*
Spot size:
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ID22NI:
High β @ 60 m, slit source, E = 17 keV 76x84 nm2: 109ph/s @ 200mA 150x100 nm2: 1012ph/s @ 200mA
ID19:
Low β @ 150 m, E = 15…24 keV 86x83 nm2: 2·1011ph/s @ 80mA
3·105 ph/s/mA/nm2
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[W/B4 C] MLs (KB system Nano-Imaging BL ID22NI)
= 8 mrad = 0.46° Focusing geometry ML structure [nm] / L [mm] q [mm] Spot [nm] Vertical [W/B4 C]25 4.9 38% 112 180 60 Horizontal [W/B4 C]25 4.9 56% 76 83 50
Courtesy
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Wave optical simulation of total reflection mirrors (M. Osterhoff)
in progress…
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Limits of x-ray focusing
Diffraction Source size Increased aperture with graded MLs Approximation Present record at Spring-8/Osaka University
0.44
FWHM
D NA S p q D
2 1
0.88 5 1 1
FWHM
D nm
KB focusing history
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