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 Seminar 21.05.10 1

Acknowledgements • Beamline Control Unit (software development) • Mechanical Engineering and Modelling (bender development) • Data Analysis Unit (theory and simulation) • Experiments Division (various beamlines) • X-ray Optics Group (metrology) • Collaborations with APS, NSLSII, Spring-8, Osaka University … Ch. Morawe - ESRF Friday Seminar 21.05.10 2

Mirrors and multilayers Basic geometry q p F S Ch. Morawe - ESRF Friday Seminar 21.05.10 3

Mirrors and multilayers Interaction of X rays with matter n 2 < n 1       1 1 Optical index n i  cos n  1 2 Snell’s law  cos n 2 1 n   cos 2 Critical angle of total reflection C n 1       2 In vacuum: e C E  Total reflection x-ray mirrors (TRM)     5 0.3 But: @ E = 10 keV: mrad C  Very long mirrors at high energies! Ch. Morawe - ESRF Friday Seminar 21.05.10 4

Mirrors and multilayers Total reflection mirror Ch. Morawe - ESRF Friday Seminar 21.05.10 5

Mirrors and multilayers Single surface reflection  Multiple reflections  Multilayer Recursive calculation of Fresnel coefficients and propagation • Parratt formalism (widely used in x-ray optics) Principle • Start at semi-infinite substrate surface (no reflection from back side) • Recursive construction of amplitudes and phases from layer to layer   f n-1,n : Fresnel coefficients  r f 4     , 1 1 , n n n n   r a E n : Electric field at centre of layer n   1 , 1  n n n 1   r f     , 1 1 , n n n n t n : Thickness of layer n Substrate R E 2  n r a  , 1 n n n E n  2 2 2     cos i t n n  0 n n  a e n 2 R  r 0 , 1 L.G. Parratt, Phys. Rev. 95, 359 (1954) Ch. Morawe - ESRF Friday Seminar 21.05.10 6

Mirrors and multilayers ML reflectivity spectra Numerical simulation Main features • Bragg peaks and fringes due to interference • Positions depend on E and Λ • Intensities depend on ∆ρ , N, σ … Corrected Bragg equation 2 2        2  2 cos m n n 2 1        >> θ C  2 sin For θ m � � A � B �� sin � Ch. Morawe - ESRF Friday Seminar 21.05.10 7

Mirrors and multilayers X-ray reflectivity measurements and simulations Simulation of x-ray reflectivity Vertical density profile 10 0 24  (Ir) 10 -1 [Ir/Al 2 O 3 ] 10 [Ir/Al 2 O 3 ] 10 20 -2 10 3 ] 16 Mass density [g/cm Reflectivity 10 -3  12 -4 10 8 -5 10 4  (Al 2    10 -6  (Si) 0 0 5 10 15 20 25 0° 1° 2° 3° 4° 5° 6°  Sample depth [nm] Ch. Morawe - ESRF Friday Seminar 21.05.10 8

Mirrors and multilayers Transmission electron microscopy (TEM) [W/B 4 C] 50 • Fabrication errors • Roughness evolution • Crystallinity • Interface diffusion Complementary to x-ray measurements ! R. Scholz, MPI Halle, Germany Ch. Morawe - ESRF Friday Seminar 21.05.10 9

Mirrors and multilayers decreasing d-spacing  increasing Bragg angle Ch. Morawe - ESRF Friday Seminar 21.05.10 10

Mirrors and multilayers Reflecting multilayer Ch. Morawe - ESRF Friday Seminar 21.05.10 11

Design and fabrication Materials choice – Basic rules 1. Select low-Z spacer material with lowest absorption ( β spacer ) 2. Select high-Z absorber material with highest reflectivity with spacer ( δ abs – δ spacer ) 3. In case of multiple choices select high-Z material with lowest absorption ( β abs ) 4. Make sure that both materials can form stable and sharp interfaces (lower d-spacing limit) Computational search algorithms • Soft X-rays: A.E. Rosenbluth (1988) • Hard X-rays: K. Vestli (1995) Areas of application • EUV lithography (E = 94 eV) • “Water window” (E = 280…550 eV) • “Hard” X rays (E = 1…100 keV) K. Vestli, E. Ziegler, Rev.Sci.Instr. 67, 3356 (1996) Ch. Morawe - ESRF Friday Seminar 21.05.10 12

Design and fabrication Filling factor (Gamma ratio) • Γ = t abs / Λ • Harmonics suppression 1 st • 2 nd Reflectivity enhancement 3 rd t space  t abs Ch. Morawe - ESRF Friday Seminar 21.05.10 13

Design and fabrication Energy resolution of multilayers – Experimental results Ch. Morawe - ESRF Friday Seminar 21.05.10 14

Design and fabrication Reflective x-ray optics - Integrated reflectivity versus energy resolution 10 0 E = 8 keV 10 -1 ESRF MLs forbidden area 10 -2 Integrated reflectivity (Mirrors/Filters) R(peak) = 100% Depth-graded ML's 10 -3 Traditional ML's High-resolution ML's Ge 10 -4 111 Si 111 10 -5 Single Crystals Be 110 10 -6 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0  Ch. Morawe - ESRF Friday Seminar 21.05.10 15

Design and fabrication Reflecting multilayer strong lateral thickness gradient  x  z weak normal thickness gradient Ch. Morawe - ESRF Friday Seminar 21.05.10 16

Design and fabrication Lateral d-spacing gradient depending on surface curvature and beam divergence Shape Parabola Ellipse Flat b sin   s p Angle  sin   sin   2 f pq f p/2 q p f f s Geometry  b     d-spacing including refraction correction m   (modified Bragg equation) 2  2  2 cos n Ch. Morawe - ESRF Friday Seminar 21.05.10 17

Design and fabrication Differential deposition  L dx         m t x R f x x  s m s v x  m L Substrate Mask Source Flux Thickness Speed  Ch. Morawe - ESRF Friday Seminar 21.05.10 18

Design and fabrication ESRF ML deposition facility Major upgrade in 2008 Loading bay Escape area Escape area Load lock Deposition zone Uniform coating area up to 1000mm x 150mm Ch. Morawe - ESRF Friday Seminar 21.05.10 19

Design and fabrication Ch. Morawe - ESRF Friday Seminar 21.05.10 20

Design and fabrication Experimental results Specular reflectivity Thickness profile Ch. Morawe - ESRF Friday Seminar 21.05.10 21

Design and fabrication Fabrication history • More than 100 devices delivered since 1998 Ch. Morawe - ESRF Friday Seminar 21.05.10 22

Performance and applications Multilayer high flux monochromators • Two bounce optics • 100x larger bandwidth compared with Si(111) • Harmonics suppression due to refraction and filling factor • Radiation and heat load issues ! Ch. Morawe - ESRF Friday Seminar 21.05.10 23

Performance and applications Total-reflection X-Ray Fluorescence (TXRF) for trace analysis (MEDEA) • Undulator source: P > 100 W @ E = 1…20 keV • Vertical double bounce ML monochromator • Two ML stripes: [Ru/B 4 C] 40 and [Ir/Al 2 O 3 ] 100 • Flux gain 100…1000 compared with Si(111) • Metal contamination on Si wafers • Detection limit < 10 10 Atoms/cm 2 (Ni) 2nd crystal Picomotor (uncooled) 1st crystal (cooled) Beam in Alignement system G. Apostolo F. Comin Copper plate Ch. Morawe - ESRF Friday Seminar 21.05.10 24

Performance and applications Double [W/B 4 C] ML monochromator for ID17 (Bio-Medical imaging) • Double bounce ML monochromator 100mm long and 150mm wide (each) • 2 uniform and identical ML coatings, both in 1 run • D-spacing mapping via x-ray reflectivity Old deposition system New deposition system [W/B 4 C] 40 : Λ = 4.0 nm [W/B 4 C] 120 : Λ = 2.0 nm Strong thickness decay (4% PV) Residual d-spacing error <1% PV Ch. Morawe - ESRF Friday Seminar 21.05.10 25

Performance and applications Double ML monochromator for ID09B (Pump and probe) • Double bounce ML monochromator after heat load chopper • Two ML stripes [Ru/B 4 C] 40 and [Ir/Al 2 O 3 ] 100 Pink beam ML beam Symmetric spectrum with dE/E = 1.6% @ 25 keV) Asymmetric spectrum @ 18 keV 0.3 s exposure 3 s exposure Si powder Courtesy M. Wulff Ch. Morawe - ESRF Friday Seminar 21.05.10 26

Performance and applications White beam exposure (K. Friedrich) • Cryogenic test bench and undulator beam • Heat load versus photon irradiation • X-ray reflectivity  ML structure, diffusion •  Surface figure Interferometry • Thermal expansion and stress Interferometer • Simulation by finite element analysis LN tank window • Improved coatings • X-rays Engineering solutions ML Ch. Morawe - ESRF Friday Seminar 21.05.10 27

Performance and applications Kirkpatrick-Baez (KB) focusing devices Albert V. Baez was the father of Joan Baez ! • Separate vertical and horizontal focusing (non-circular source) • Technologically easier than single reflection ellipsoid • Metal or graded ML coatings P. Kirkpatrick, A.V. Baez, J. Opt. Soc. Am. 38, 766 (1948) Ch. Morawe - ESRF Friday Seminar 21.05.10 28