X-ray Microscopy 2002

Transcription

1 X-ray Microscopy 2002 July 29 August 2, 2002, Grenoble,, France Main Organizer: Jean Susini (ESRF) Oral & poster presentations 239 registrants 49 PhDs Visit to ESRF Dinner at Chateau d Herbelon Highlights of XRM'02 Novel optics Phase contrast More hard x-rays x Lots of applications

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4 Background on X-ray X Microscopy ESRF ID21: TXM 3-6 kev ESRF ID21: SXM 2-10 kev & < 2keV Two types: full field & scanning transmission fluorescence XPEEM All types of materials are studied, from biological to magnetic Increasing number of SR imaging microscopes worldwide due to availability of => high-resolution lens-like optics: zone plates, KB mirrors, CRLs => high-brilliance synchrotron sources

5 Nanofabricated Diffractive Optics Linear zone plates: C. David (PSI) Multilevel zone plates: Fabrizio (Elettra) & David (PSI) Complex zone plates: Di Fabrizio (Elettra) Wilhein (Remagen, Germany) Photon sieves: P. Charalambous (King s College) 1D & 2D wave guides: T. Salditt (U. Saarbrucken) Diamond refractive lenses: A. Freund (ESRF) 68.7nm x 33.0nm (derived)

6 Linear zone plates: C. David (PSI) Matching anisotropic source shape & size Tilted to increase ZP s efficiency

7 Multilevel Zone Plates: C. David (PSI) Di Fabrizio, Nature (1999)

8 Photon Sieves: P. Charalambous (King s College) L. Kipp et al., Nature (2001)

9 Complex zone plates: Di Fabrizio (Elettra) Wilhein (Remagen, Germany) 2 spots 4 spots Multiple focal spots in single or multiple focal plane for differential interference contrast microscopy Complete beam shaping for maskless lithography & x-ray x induced CVD 2 spots longitudinal

10 Differential Interference Phase Contrast with ZP Doublet Wilhein et al. APL 78, 2082 (2001). ESRF, ID21, 4 kev PMMA 2µm-thick: 98.7% transmission Giant moss spores of Dawsonia superba

11 X-ray Shearing Interferometer: C. David (PSI) Calculation Si phase grating beam splitter Experiment polystyrene spheres of 0.1mm and 0.2mm

12 Some Examples on Applications Nano-tomography on AMD K6: Magnetic imaging with XMCD: 3D XRD mapping of grains: C.G. Schroer (Aachen) A. Snigirev (ESRF) P. Fischer (MPI, Stuttgart) G. Denbeaux (ALS) H. Poulsen (Riso) B. Larson IUCr Element mapping in biological samples: C.G. Schroer (Aachen) A. Snigirev (ESRF) Spectromicroscopy of polymers: Cryo tomography soft x-rays: A.P. Hitchcock (McMaster) C.A. Larabell (Anatomy, UCSF) Many many more Yeast: single celled eukaryotic organism, ~5µm in diameter

13 Nano-tomography on AMD K6: C.G. Schroer (Aachen) A. Snigirev (ESRF) ID22 ESRF: parabolic Al refractive lens imaging onto 2D detector x-ray energy 25 kev magnification 20.9x 3D resolution 410nm

14 Fluorescence Microtomography with Micro-beam beam: C.G. Schroer (Aachen) A. Snigirev (ESRF) ID22 ESRF: parabolic Al refractive lens focal spot: 3 µm x 0.9 µm scan step: 1 µm 132 projections in 360 o Specimen: mycorrhyzal root of tomato plant, grown on heavy metal polluted soil

15 Full Field Fluorescence Microscope Ohigashi, Watanabe, Yokosuka & Aoki, JSR 9, 128 (2002). Fe Co Ni Cu 1Kx1K CCD: 12µm x 12µm pixels, photon counting => 10:1 magnification Pt-coated Pyrex

16 Full field magnetic imaging with XMCD: P. Fischer, G. Schutz (MPI, Stuttgart) G. Denbeaux, D. Attwood (ALS)

17 No polarity switching necessary Contrast reversal between L3 & L2 Compared to EM: no effects from applied H Fe L 3 & L 2 Fe 4A / Gd 4A x75

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19 Magnetic Nanostructures Eimuller et al. Appl. Phys. A (2001) Landau patterns

20 Eimuller et al. Appl. Phys. A (2001) Fe/Gd 190nm dots In-plane domains

21 Imaging Magnetic Bits in Magneto-optical optical Film Fischer et al. JSR (2001) Thermomagnetic recording by laser-pumped magnetic field modulation

22 Undulation Instability in Magnetic Nanowires Eimuller et al. JAP (2002) Multilayer: (4A Fe/4A Gd)x75 on 300nm Si 3 N 4 8nm Al cap layer E-beam lithography: 2µm to 100nm lines H

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24 Spin dynamics on nanostructured magnets with pump-probe probe Deneaux et al. XRM (2002) micro-coil with pulser (rise time ~100ps) x-ray pulse from ALS (Fwhm<70ps, 3MHz) pump-probe delay (0 < t < 328ns)

25 Highlights on Phase Contrast Zernike phase contrast: Phase contrast in STXM: Differential phase contrast: Y. Kagoshima (Spring-8) U. Neuhausler (ESRF) M. Feser (SUNY-SB) G. Morrison (Kings College) T. Wilhein (U. Koblenz, Germany) Phase contrast tomography: P. Cloetens, J. Baruchel (ESRF) Shearing interferometry: Diffraction microscopy: C. David (PSI) J. Miao (SSRL) M. Howells (LBNL) J. Kirz & D. Sayre (SUNY-SB) Nanocrystal diffraction imaging: I. Robinson IUCr

26 Absorption Contrast vs. Phase Contrast Refraction index: n = 1 δ iβ absorption contrast: µz = 4πβz/λ λ 3 phase contrast: φ(z) = 2πδz/λ λ z Phase contrast (with Ta phase plate) Phase contrast is x10 4 higher than absorption contrast for protein in 8keV Dose reduced to level comparable to using water-window in soft x-ray region Kirz (1995): 0.05µm protein in 10µm thick ice C 94 H 139 N 24 O 31 S Absorption contrast Dose (Gray) absorption contrast Kagoshima et al. (2001): protein C 94 H 139 N 24 O 31 S ρ=1.35g/cm 3, t=0.1µm in 10µm water phase contrast X-ray Energy (ev)

27 Principle of Zernike Phase Contrast (Born & Wolf) For pure phase object: F(x) = e iφ(x) ~ 1 + iφ(x) => No absorption contrast: F 2 ~ 1 Zernike method in visible optics: phase plate: φ=±π/2 in zeroth-order => F'(x) ~ ±i + iφ(x) => Phase contrast: F' 2 ~ 1 ± 2φ(x)

28 Zernike Phase Contrast for x-raysx Soft X-rays: Schmahl et al. (1995). BESSY, 0.5 kev. Hard X-rays: Kagoshima et al. (2001). SPring8, 10keV. 3-5 minutes exposures at SPring-8 undulator BL24XU Conidium of Curvularia species

29 Zernike Phase Contrast More recent: Kagoshima et al. JSR 9, 132 (2002). SPring-8 BL24XU Cu mesh Polystyrene spheres D=7µm

30 Phase Contrast in STXM M. Feser, C. Jacobsen, XRM (2002). pin-diode Multi-segment detector M. Feser: recipient of Meyer-Ilse Award on XRM (2002).

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33 Phase Contrast in STXM with CCD G. Morrison (King s College) Software-configurable CCD:! absorption! phase contrast! dark field TXM multi-element 80x80 CCD 3 3keV uncooled => simultaneous detection of both δ and β on the same sample area Phase contrast modes:! 1 st moment! 1 st moment x = x I y = y I! measures phase gradient i i ( i i x, y ) ( i i x, y ) STXM TXM and STXM:! related by optical reciprocity! detector in STXM " extended source in TXM

34 M. Feser, Ph.D Thesis (2002). phase-contrast below C K-edge for biological specimens?

35 Phase Retrieval in Phase-Contrast Imaging Phase Retrieval: I(u, v) # ρ(x, y) =? Propagation based method: Teague, J. Opt. Soc. Am. 4, 118 (1987) Gureyev et al., J. Opt. Soc. Am. 12, 1942 (1995) Nugent et al., PRL 77, 2961 (1996) Paganin & Nugent, PRL 80, 2586 (1998)

36 $ Phase is defined by: (i) index of refraction n(r) k 0 z n = 1 δ + i β k = n k 0 e ikz ~ k 0 n(x,y,z) dz (ii) energy flow S(r) E = E(r) e ik r = E(r) e iφ(r) φ = (k r) = k = propagation direction $ Transport of intensity equation Poynting vector: S(r) ~ E 2 k ~ I φ Energy conservation: S = 0 => (I φ) = 0 # Solution of φ from intensity I(r)

37 Phase Imaging & Tomography λ Cloetens et al. (1999): ESRF, ID19, 18 kev Polystyrene foam 0.7x0.5x1mm 3 1.4T wiggler, B~7x10 14 ph/s/mr 2 /mm 2 4x700 images at 25 sec/image A form of Gabor in-line holography Coherence over 1st Fresnel zone (λr) 1/2 Image reconstruction (phase retrieval) Spatial resolution limited by pixel size

38 Phase Contrast Microscopy by Defocusing Allman et al. JOSA (2000). APS, 2-ID-B, 1.8 kev spider silk fiber: φ1.7µm holographic geometry retrieved phase: 2.5 rad imaging geometry

39 Diffraction Microscopy Diffraction microscopy is analogous to crystallography, but for noncrystalline materials Coherent diffraction from noncrystalline specimen: => continuous Fourier transform Spatial resolution: essentially no limit. (only limited by λ/λ and weak signals at large angles) Coherence requirement: coherent illumination of sample Coherent X-rays Key development: oversampling phasing method coherent flux!! Miao et al. (1999) >>> soft x-rays, reconstruction to 75 nm

40 Diffraction Microscopy most recent results Miao et al. (2002) λ = 2 Å reconstructed image: to d~7nm resolution Gold: 2.5µm x 2µm x 0.1µm SPring-8 undulator BL29XU: standard 140 periods λ u =3.2 cm B=2x10 19 ph/s/mr 2 /mm 2 For Au, exposure time 50 min, d~7nm But: for C, (Z c /Z Au ) 2 ~1/173 => 6 days!!

41 3D Structures with Coherent Diffraction λ=2å Coherent diffraction microscopy: Miao et al. (2002). Two nickel plates: 2.8x2.6x1.2µm 3 SPring-8, BL29XU Reconstructed to 55nm resolution in 3D, based on 30 frames in 5 o steps, 20 min/frame, ~10hrs. Single molecule imaging??

42 More Phase Contrast Fourier Transform Holography Leitenberger & Snigirev (2001) Coherent nanocrystals diffraction Robinson et al. (2001): 1µm Au nanocrystal Au (111) Imaging of shape and strain in nanocrystals particle-size broadened Bragg peaks help solving phase problem due to oversampling

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44 Vartanyants & Robinson J. Phys.: Cond. Matter 13, (2001). Partial coherence => small areas of high intensitied in reconstructed images

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46 Model Free Strain Profile? Shen & Kycia (1997) PRB 55,

47 ERL Spatial Coherence ESRF emittance (4nm x 0.01nm) Diffraction 8keV ERL emittance (0.015nm) Diffraction limited source: 2πσ'σ = λ/2 or ε = λ/4π Almost diffraction limited: 2πσ'σ ~ λ or ε ~ λ/2π Cornell ERL: : diffraction-limited source E < 6.6 kev almost diffraction-limited to 13 kev

48 Spatial Coherence a few definitions 2σ 2σ' 2σ ~ λ 2σ' 2σ σ' l = σ' 2σ = λ/2 => X-ray beam is spatially coherent if phase-space area 2πσ σ < λ/2 Diffraction limited source: 2πσ'σ = λ/2 or ε = λ/4π Almost diffraction limited: 2πσ'σ ~ λ or ε ~ λ/2π

49 Source Emittance and Brilliance Phase-space space Emittance: EM wave: E(r, t) = E 0 e i(k r ωt) x x Integrated total flux F n x ε x = σ x σ x σ x y ε y = σ y σ y σ y σ E E ε τ = σ τ σ E / E σ x x σ y y σ τ t Brilliance: : photon flux density in phase-space space Average B = F n (2π) 2 ε x ε y Peak B ^ = F n (2π) 3 ε x ε y ε τ

50 Benefits of ERL to XRM Brings high coherence to hard x-ray regime Better optical performance for STXM & µ-probe Phase imaging & microscopy Far-field diffraction microscopy Holographic techniques Time-resolved and flash microscopy Larger depth of focus for tomography & 3D structures Coherent Crystallography, etc.

51 Micro-focusing Bilderback (2000) ERL Workshop D 1 D 2 Sigma x Sigma x Sigma y Sigma y (µm) (µr) (µm) (µr) ESRF Microfocus BL Advanced Photon Source Energy Recovery Linac nm, 100 ma, 25 m ID Energy Recovery Linac nm, 10 ma, 2 m ID Require slope error δθ << σ x / D 1 = 3.9 µm / 40 m = 0.1 µrad

52 High Resolution X-ray X Microscopy? TEM like microscropy for hard X-raysX rays? Thin crystal object plane back focal plane image plane Would it be possible to image atomic planes (atoms) in a crystal thin enough for x-rays? TEM without sample preparation!!!

53 Summary X-ray microscopy is an exciting field due to advances in focusing optics, 2D detectors, better sources, precise mechanics, & phasing algorithms Lots of old ideas for TEM and optical microscope are now being tested and applied for hard x-raysx Lots of application possibilities CHESS can make substantial contributions due to our existing interests in optics, detectors, ERL, x-ray physics, phasing methods, & nanofabrication

54 X-ray Microscopy 2002 Incident beam sample Detected beam Microscope condensed stationary transmitted Imaging plane or spherical wave stationary transmitted, refracted Scanning Probe focused scanned transmitted, fluorescence, or refracted Diffraction coherent stationary scattered Interferometer split stationary interference