Matias Bargheer. Ultrafast X-ray Diffraction: Picosecond acoustics and related scientific cases

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1 Matias Bargheer Ultrafast X-ray Diffraction: Picosecond acoustics and related scientific cases Intro: Why femtosecond x-ray diffraction? Some important basics on x-ray diffraction. Available sources use what you need! Scienctific cases state of the art Recent developments UXRD on multilayers

2 Understand Function by Watching Movies Analyze a series of snapshots

3 Intro: Why femtosecond x-ray diffraction? Intro: Why femtosecond x-ray diffraction? Some important basics on x-ray diffraction. Available sources use what you need! Scienctific cases what do we learn from them?

4 Why do we need pump-probe? Watch an aimless crowd of people Watch dancers excited by music Only statistical observables: Mean amplitude Mean velocity (solution: single one out!) Additional observables: Phase lag of music and people Function: What happens when music stops

5 Atomic Movies Recorded by Ultrafast XRD

6 Coherent Motion Connected to Function What is the difference? Thermal motion Thermal + coherent motion

7 Coherent Motion Connected to Function What is the difference? Thermal motion at T = 0K Thermal + coherent motion

8 Structural Dynamics Thermal motion: Matter is in thermal (random) motion Energy E = ½ kt per degree of freedom (equipartition = stationary) Nonequilibrium motion: Pump-Probe techniques An external stimulus can induce particular motion in specific coordinates In condensed matter, energy will dissipate within 1 ps 1 ns The coherent motion (phase of motion reproducibly conected with the external stimulus) can be measured by pump-probe techniques. Structural Dynamics (atomic resolution): optical pump / x-ray probe X-ray absorption (EXAFS) X-ray diffraction (scattering)

9 Ultrafast X-ray Diffractometer X-ray diffraction Direct determination of structures Resolution 100 fm Stroboscope (Pump-Probe) Transition states, non-equilibrium Resolution 100 fs ~ 10 6 photons /s on sample Femtosecond Laser Delay Stage X-ray plasma 150 μm = 1ps X-ray optic Goniometer k 2θ X-ray detector k CCD G Shielded detection unit

10 Some important basics on x-ray diffraction. Intro: Why femtosecond x-ray diffraction? Some important basics on x-ray diffraction. Available sources use what you need! Scienctific cases what do we learn from them?

11 X-ray Imaging: Limited by Source Size Optical Microscope Resolution limited be wavelength: ~ 0.5 μm = m X-ray-wavelength m X-ray Shadow Image Resolution limited by source size: ~ 1 μm = 10-6 m We want atomic resolution ~ 1 pm = m

12 X-ray Diffraction Mainly core-electrons contribute to the scattered wave. Scattering cross-sections for ALL elements are tabulated!

13 X-ray Diffraction

14 } X-ray Diffraction k λ k k = k =2π/λ

15 X-ray Diffraction d{ k k G k = 2π/λ Laue-condition: k k = G Reciprocal lattice vector: G = 2π/d Bragg-law: λ = 2d sin(θ)

16 X-ray Diffraction = Fourier-Transformation The x-ray scattering amplitude is the Fourier-transform of the electron density Mathematically: iqr A( q) = ρ( r) e dr Fourier-Transformation is the Separation in plane waves. k The Laue-condition is fulfilled, when Wave-vectors change q = k k equals a reciprocal lattice vector. k q = G => Peak

17 X-ray Diffraction = Fourier-Transformation Photosynthetic reaction center Barium-Titanate crystal

18 Scattering from Crystal Structures Lattice: Basis: Crystal structure: a 1 a2 Lattice points at: Atoms at: Electron density: Scattering amplitude: iqr A( q) = ρ( r) e dr Peak Intensity Peak position

19 Available Sources use what you need Intro: Why femtosecond x-ray diffraction? Some important basics on x-ray diffraction. Available sources use what you need! Scienctific cases what do we learn from them?

20 Ultrafast X-ray Diffractometer X-ray diffraction Direct determination of structures Resolution 100 fm Stroboscope (Pump-Probe) Transition states, non-equilibrium Resolution 100 fs ps / slicing 100 fs Femtosecond Laser Delay Stage X-ray plasma Storage ring 150 μm = 1ps X-ray optic Goniometer k 2θ X-ray detector k CCD G Shielded detection unit

21 Ultrafast Experiments in Potsdam Bessy II in Berlin X-ray plasma source Ultrafast optical (IR UV)

22 Generation of Ultrashort X-ray Pulses

23 UXRD: Setup and Signal 1 khz, 5 W 45 fs, 800 nm 1 khz, 5 W 45 fs, 800 nm delay stage delay stage x-ray CCD x-ray CCD SL peaks Thick SRO layer debris protection pump pump x-ray probe x-ray mirror Cu-band Cu-band target target SLsample SLsample ΔΘ / Θ 0 (x10-3 ) Reflectivity (0 0 55) (0 0 56) Θ(deg) Delay Time (ps) ΔR/R 0 ~ phonon amplitude Δd / d 0 (x10-3 )

24 Plasma Source vs. FEMTO-Slicing 0.05 Slicing beamline (I pump = 4 mj/cm 2 ) Plasma-Source (I pump = 8 mj/cm 2 ) ΔR / R ~ 30 min time (ps)

25 Scientific Cases Intro: Why femtosecond x-ray diffraction? Some important basics on x-ray diffraction. Available sources use what you need! Scienctific cases what do we learn from them?

26 UXRD: Technology X-ray diffraction Peak position Peak Intensity Fourier-Trafo of atomic positions Lattice constants Structure factor = position of atoms in unit cell Synchrotron: 100 ps time resolution kinetics of complex systems photons/s on sample (ID 9) Laser-Plasma Sources: 100 fs time resolution Dynamics of simple systems 10 6 photons/s on sample low-α mode slicing schemes x-ray optics tabletop synchrotron Free-Electron-Laser Stanford (LCLS), Hamburg (XFEL)?

27 Functions and Reactions Physics: Collective dynamics e - - phonon interaction Excitation Non-equilibrium Dynamics Energy relevant coordinate Soft matter: Photobiology Chemistry: Non-adiabatic molecular dynamics Quantum chemistry

28 UXRD: Experiments Physics: Coherent phonons in Bi UXRD Biology: Photodynamics of CO in Myoglobin Bild: M. Wulff K. Sokolowski-Tinten et al., Nature 422, 287 (2003) Chemistry: nonadiabatic molecular dynamics in solution Schotte et al., Science 300,1944 (2003) A. Plech et al. PRL 92, (2004)

29 Ultrafast X-ray Diffraction: Experiments Physics: Coherent Phonons Raman vs. DECP Soft matter: Small angle scattering from gold-nanoparticles Chemistry: C 2 H 4 I 2 dissociation Plech et al., Nature Physics 2, 44 (2006) Bargheer et al., Science 422, 287 (2004) Ihee, Science, 309, 1223 (2005) + JACS, 130, 5834 (2008)

30 Ultrafast Chemistry in Liquids

31 Signal Changes in Crystals (a) (b) (c) (d) disorder intensity reduction exp(-<u G 2 >G 2 ) hom. acoustic deformation tensile/compressive line shift LA phonon G lattice +/- Q phonon sidebands hom. optical deformation pos. / neg. intensity modulation α u (e) (f) (g) (h) d k G=2 π/d k Bargheer et al., ChemPhysChem 7, 783 (2006)

32 Ultrafast nonthermal melting of InSb Debye-Waller: Lindenberg et al., Science 308, 392 (2005)

33 Expansion in SrRuO 3 Thin Films Thin film substrate 2Θ K α1 K α2 Korff Schmising et al., Appl. Phys. B 88, 1 (2007) Woerner et al. Appl Phys A 96, 83 (2009)

34 Acoustic Phonons in GaAs Sidebands of Bragg Peaks White phonon spectrum is generated. Observe oscillation of LA phonon with wavevector selected by diffraction condition Lindenberg et al., PRL 84, 111 (1999)

35 Bismuth Plasma Source S(hkl) 2 (222) S hkl = i f i e ig hkl r i (111) x equilibrium distance x = 0.5 displaced quasi-equilibrium distance Sokolowski-Tinten et al., Nature 422, 287 (2003)

36 Bismuth - SPPS Fritz et al., Science 315, 633 (2007)

37 Bismuth Grazing Incidence at SLS Johnson et al., PRL 100, (2008)

38 Signal Changes in Crystals (a) (b) (c) (d) disorder intensity reduction exp(-<u G 2 >G 2 ) hom. acoustic deformation tensile/compressive line shift LA phonon G lattice +/- Q phonon sidebands hom. optical deformation pos. / neg. intensity modulation α u (e) (f) (g) (h) d k G=2 π/d k Bargheer et al., ChemPhysChem 7, 783 (2006)

39 ZFLAP in Semiconductor Superlattices z Dispersion: Zone Folded Longitudinal Acoustic Phonons: ZFLAP pump CB VB ω t < 0 t = 0 t = T/2 t = T 0 π d SL Bargheer et al., Science 306, 1771 (2004) k π a 0

40 Ultrafast X-ray Diffraction on Superlattices ΔR / R 0 ΔΘ / Θ 0,01 0,00-0,01-0,02-0,03 1x x10-4 ν (THz) 0,0 0,5 1, THZ time delay (ps) FFT Power Measurement: Oscillation around displaced equilibrium Phase of oscillation: Cosine No lineshift Results: Time resolution t ~ 100 fs Structural resolution Δa B = 80 fm Δa B /a B = Excitation mechanism: DECP Bargheer et al., Science 306, 1771 (2004)

41 Raman vs. Displacive Excitation 1000 DECP Real carriers Dynamics in presence of carriers Cosine ε / J m S Amplitude Force time Strain S = Δa / a 0 Raman Virtual or resonant Dynamics in electronic ground state Sine ε / J m S Strain S = Δa / a 0 Amplitude Force time

42 All-Optical Detection of Superlattice Phonons InGaN / GaN Pump + probe below bandgap Pump + probe above bandgap Time delay (ps) Raman-Excitation Coherent phonons in ground state Free carriers screen piezoelectric field DECP (displacive excitation) T. E. Stevens, J. Kuhl, and R. Merlin, Phys. Rev. B., 2002, 65, Bartels et al., Phys. Rev. Lett. 82, 1044 (1999) Sun et al., Phys. Rev. Lett. 84, 179 (2000)

43 Metal/Dielectric Superlattice SRO/STO Independent of pump wavelength (800, 1280, 2200 nm) ~ c SRO Forced oscillator: x ~ Δc SRO d 2 +ω0 2 x 2 d t 1 x = m F( t) Rise time of force τ rise = 500 fs Pressure by hot phonons Woerner et al., Appl.Phys. A. 96, 83 (2009)

44 Potsdam-Berlin Berlin Potsdam Bessy II in Berlin

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48 Team University of Potsdam Wolfram Leitenberger Roman Shayduk Hengameh Navirian Yevgeni Goldshteyn Mareike Kiel Lena Maerten Steffen Mitzscherling André Bojahr Madlen Klötze Peter Gaal Marc Herzog Daniel Schick Clemens v. Korff Schmising Matias Bargheer Financial support: BMBF, DFG Max-Born-Institute MBI: C. von Korff Schmising Z. Ansari A. Harpoeth F. Zamponi M. Woerner N. Zhavoronkov T. Elsaesser Swiss Light Source Chris J. Milne Renske Van der Veen Steven L. Johnson MPI für Mikrostrukturphysik Dietrich Hesse, Marin Alexe, Ionela Vrejoiu

49 Oxide Nanolayers Perovskite structure Ferromagnetic SRO /STO metals: SL 0,1 ΔR / R Vrejoiu et al., APL 92, (2008). ΔR / R 0,01 1E-3 1E-4 0,1 0,01 1E-3 1E-4 1E-5 1E-6 1E-7 SRO: SrRuO 3 T c 160 K (bulk) LSMO: (La 0.7 Sr 0.3 )MnO 3 T c 370 K (bulk) Insulators: 1E-5 3,16 3,17 3,18 3,19 3,20 3,21 3,22 3,23 3,24 3,25 3,26 STO: SrTiO 3 dielectric q / nm -1 PZT: LSMO Pb(Zr /PZT 0.2 Ti SL 0.8 )O 1 3 ferroelectric below T c 750 K Other perovskite oxides: Superconducting, giant magnetoresistance,.. Rich phase diagrams > Grown 19by Pulsed 20 Laser 21Deposition MPI Halle: D. Hesse, θ / M. degalexe, I. Vrejoiu

50 Phonon Lattice Electrons Spins Orbitals Multiferroics / correlated sytems: Coupling strengths Interaction timescales strain ε polarization P piezoelectric screening electrons Stoner excitation magnetoelectic Electron- magnetostrictive magnetiziation M 50

51 Optical Excitation of Oxide Nano-Layers SRO PZT SRO PZTSRO PZT SRO Expectation: Excitation of electrons in metal (SRO) Expansion of SRO compression of PZT standing Wave Layer-thickness / sound-velocity ~ 2 ps Questions: How does electron-excitation induce nuclear motion? (e ph coupling) Are specific modes coupled? Magnetization? Polarization?

52 All-optical pump-probe setup beam splitter BBO / NOPA probe beam pump beam Ti:Sa fs laser + regenerative amplifier reflection detector delay line white light generation focussing Element sample transmission detector 52

53 All optical data: Transient reflectivity SRO / STO multilayer, pump 800 nm, 40.2 mj/cm 2 probe white light Probe wavelength 3,2 ps time

54 Sound Waves: Phonon Simulations Aplitude of mode / arb. u. 1 0,1 0,01 1E-3 1E-4 1E-5 1E-6 50 nm abs. depth w/ substrate hom. abs. w/ substrate hom. abs. only SL 0 1 ω / ωsl 2

55 Sound Waves: Phonon Simulations 0,12 0,10 0,08 0,06 0,04 Only SL SL with substrat position z / unit cells ,10 0,05 0,00-0,05-0,10 amplitude amplitude 0,02 0,00-0,02-0,04-0,06-0,08-0,10 superlattice substrate position z / unit cells

56 Sound Waves: Phonon Simulations

57 Sound Waves: Phonon Simulations 1. Electronic excitation (intraband) 2. Phonon modes and photoelastic effect (dn/dε) 3. Interference of light reflected off surface and traveling strain pulse time depth Spatio temporal strain distribution

58 Measure Lattice Deformation Directly Additional parameter: expansion of structure Measure shift + intensity to get STO and SRO change Korff Schmising et al., Physics Procedia. 3, 333 (2010)

59 Fluence Dependence Δη / η after 1.5 ps after 200 ps η ~ ΔR/R 0 SRO PZT Excitation Fluence (mj/cm 2 ) Δη / η SRO STO Excitation Fluence (mj/cm 2 ) Strain vs. fluence linear up to η = c/a = 2% 1 GPa pressure switched on in 550 fs Expansion is non-thermal (Temperature different in SRO/STO) Even after 200 ps!! Superlattice phonon dispersion is flat no propagation No wavelength dependence: Hot phonons in SRO Woerner et al., Appl.Phys. A. 96, 83 (2009)

60 Heat Dissipation - Nanoseconds LSMO/STO SL on STO substrate temperature change, C T SL, calculated T sub, calculated T SL, SL T sub, Substrate Temperatures experimentally derived from peak position and bulk expansion coefficient Temperature calculated from bulk heat conductivities Initially fast cooling? Stress from electrons? delay, ns

61 X ray diffraction from Multilayers Convolution Theorem: FT ( f g ) = FT ( f ) FT ( g ) D SL Fourier Transf. d SRO d STO Diffraction Intensity D SL g SL = 2π/D SL Θ (deg) 61 Double- SL- = SLlayer Period Structure

62 X ray diffraction from Multilayers Convolution Theorem: FT ( f g ) = FT ( f ) FT ( g ) D SL Fourier Transf. d SRO d STO Diffraction Intensity D SL g SL = 2π/D SL Θ (deg) 62 Double- SL- = SLlayer Period Structure

63 BESSY and SLS- FEMTO-Slicing ΔR / R 0,1 0,01 1E-3 1E-4 SRO/STO SL 1.6 ps after excitation! 1E-5 3,16 3,17 3,18 3,19 3,20 3,21 3,22 3,23 3,24 3,25 3,26 q / nm -1 Herzog et al., Appl.Phys. Lett. 96, (2010)

64 ΔR / R 0,1 SRO/STO SL 1.6 ps 0,01 1E-3 1E-4 1E-5 3,16 3,17 3,18 3,19 3,20 3,21 3,22 3,23 3,24 3,25 3,26 q / nm -1 tot Expansion of entire superlattice: (oscillations damped out) intensity (a.u.) Expanison and Inhomogeneous Excitation unpumped 7.3 mj/cm mj/cm mj/cm mj/cm ,8 36,9 37,0 37,1 37,2 37,3 37,4 Θ / T 800 nm excitation shift = D v LA 37ps From deposited energy/ heat capacity ΔT = 600 K Observed shift + Debye Waller factor: Lattice temperature ΔT ~ 1800 K Expansion three times larger than bulk? Epitaxial condition?

65 Expanison and Inhomogeneous Excitation time depth Peak-shift Expansion of SL ~ 1.1% Peak-Broadening Variation of layer-thickness Peak-Assymetry Exponentially decaying exc. increased for 400nm pump T shift = D v tot LA 37ps intensity (a.u.) unpumped 7.3 mj/cm mj/cm mj/cm mj/cm nm excitation unpumped 400 nm excitation -0,015-0,010-0,005 0,000 ΔΘ / Θ 0 intensity (a.u.) mj/cm mj/cm mj/cm 2-0,005 0,000 Θ /

66 Strain Wave In Substrate intensity (a.u.) mj/cm mj/cm 2 unpumped 0-0,005 0,000 0, ps 74 ps 800 nm excitation 400 nm excitation 37 ps intensity / a.u unpumped 39 ps, 240mW 39 ps, 330mW 73 ps, 330mW -0,005 0,000 0,005 ΔΘ / Θ 0 ΔΘ / Θ 0

67 R p -R 0 R p -R 0 counts 0,06 0,04 0,02 0,00-0,02-0,04 0,03 0, ,03 No Shift! Splitting! 30 LSMO/STO SL, peak +1 unpumped ~ 20 mj/cm 2 10 ps 20 ps M 25 Y 30 ps V S P O 40 ps 300 ps 15 B C C8 C32 C42 C51 Electrode layer expansion Watch sound wave propagate through superlattice R p = I p /I ,04 5 0,02 0,00 0 3,19 3,20 q / nm substrate 1,45 1,50 1,55 1,60 1,65 1,70 pitch ( )

68 ΔR / R ΔR / R depth 0,0-0,2-0,4-0,6-0,8 Standing Wave: Period 3.2 ps time 0,1 0,01 1E-3 1E-4 1E-5 3,16 3,17 3,18 3,19 3,20 Ultrafast 3,21Bragg-switch! 3,22 3,23 3,24 3,25 3,26 q / nm % increase! 20.6 mj/cm mj/cm mj/cm 2-1, time delay (ps) Amplitude of wave: SRO expanded by 1.8%! Decay time: 10 ps Period 3.2 ps Structure factor depends nonlinearly on amplitude! ΔR / R delay time (ps) 39.2 mj/cm mj/cm 2

69 Switching on the Structure Factor Nonlinear response to strain Spikes rather than oscillations Temporal width of 1 ps!! 1 ps rise factor strain Δc/c 0 Herzog et al., Appl.Phys. Lett. 96, (2010) The phonon Bragg switch: Bucksbaum+Merlin, Sol.Stat.Commun. 111, 535 (1999) Shepphard et al., Sol.Stat.Commun. 136, 181 (2005)

70 New Beamline Layout Schematic experimental setup at EDR beamline (bending magnet) at BESSY II for time resolved XRD and XAS ( kev) Monochromator incl. Laser driven X ray switch (2) No timing jitter Use swiched X rays in hybrid or single bunch mode ~10 8 photons/s More at undulator 70

71 Optical Excitation of the Metal SRO ~ c SRO Independent of pump wavelength (800, 1280, 2200 nm) Forced oscillator: x ~ Δc SRO d 2 +ω0 2 x 2 d t x 1 m F( t) Rise time of force τ rise = 500 fs ~1 GPa in 1 ps. Reversible. Pressure by hot phonons = Woerner et al., Appl.Phys. A. 96, 83 (2009)

72 Optical Excitation of Magnons in SRO SRO is ferromagnetic for T < T C = 160K Reduced phonon amplitude Contraction by magnetostriction partially compensating thermal expansion Amplitude Korff Schmising, Phys Rev. B. 78, (R) (2008)

73 Optical Excitation of Magnons in SRO Amplitude mimics magnetization energy ~ M 2 Wavelength dependence! 1.0 Amplitude Amplitude T C = 160 K 0.4 λ ex = 0.8 μm λ ex = 2.2 μm T (K) Korff Schmising, Phys Rev. B. 78, (R) (2008)

74 Optical Excitation of Magnons in SRO SRO is ferromagnetic for T < T C = 160K Reduced phonon amplitude Contraction by magnetostriction partially componsating thermal expansion Magnetostrictive force faster than ~ 500fs Korff Schmising, Phys Rev. B. 78, (R) (2008)

75 Reviews: Clemens v. Korff Schmising et al, Z. Kristallogr. 223, (2008) M. Bargheer, Atombewegung im Röntgenkino Physik Journal 8, (2007) M. Bargheer et al., ChemPhysChem, 7, (2006) Klaus Sokolowski-Tinten, J. Phys.: Condens. Matter 16, R1517 R1536 (2004) A.Rousse et al., Rev. Mod. Phys. 73, 17 (2001)

76 Summary Basics X-ray diffraction Plasma source vs. FEMTO-sliing Classification of ultrafast changes UXRD amplitude + phase Scientific cases from chemistry and physics Sound in SL Sound = Interference of Eigenmodes Raman vs. displacive excitation Heat expansion: phonon-phonon interact. Oxide superlattices: 1.8% strain! Ultrafast nonlinear X-ray Bragg switch Ultrafast magnetostriction 1000 (a) (b) (c) (d) 500 ε / J m -3 0 disorder intensity reduction exp(-<u 2 G >G 2 ) (e) hom. acoustic deformation tensile/compressive (f) line shift LA phonon G lattice +/- Q phonon sidebands (g) hom. optical deformation pos. / neg. intensity modulation α u (h) S