X-Rays and Materials A Vision of the Future Joachim Stöhr Stanford Synchrotron Radiation Laboratory.
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X-Rays and Materials A Vision of the Future Joachim Stöhr Stanford Synchrotron Radiation Laboratory The big $$$ Picture: US Gross Domestic Product: $10 Trillion In $$$$$'s Information technology: 800 Billion Chemical Industry: 400 Billion Semiconductors: Magnetic materials: 80 Billion 25 Billion Pharmaceutical industry: 220 Billion Biotech Industry: 30 Billion Modern materials are complex – studies require sophisticated techniques Present: Size > 0.1 mm, Speed > 1 nsec Future: Size < 0.1 mm, Speed < 1 nsec Ultrafast Nanoscale Dynamics Growth of X-Ray Brightness and Magnetic Storage Density Why X-Rays? - Chemical Sensitivity Core level shifts and Molecular orbital shifts Stöhr et.al Polarization Dependence C C E F F C C F F F F Normalized Intensity (a.u.) Normal Incidence Grazing Incidence C F C O F F C E C C F F C F F8 22°C 290 295 Photon Energy (eV) 300 305 C F F Magnetic Spectroscopy and Microscopy Real Space Imaging X-Rays have come a long way…… 1895 1993 Photoemission Electron Microscopy – PEEM at ALS The Future: PEEM3 Resolution PEEM2 nm PEEM3 nm 50 nm < 5 nm (1% transmission) Transmission 1% @ 50 nm Resolution 50% Relative photon flux 1 20 Relative Flux density 1 >1000 bend EPU (arbitrary) Source / Polarization PEEM2 on BL 7.3.1.1 4.0.3 PEEM3 Microscope - total electron yield imaging - no LEEM mode (as in SMART) Resolution vs Transmission Spectromicroscopy of Ferromagnets and Antiferromagnets AFM domain structure at surface of NiO substrate s [010] s 2mm NiO XMLD 0.10 8 TEY (a.u.) TEY (a.u.) 0.15 0.05 Co XMCD 4 0 0.00 868 870 872 874 Photon Energy(eV) 777 778 779 Photon Energy (eV) H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), 2878 (2001). FM domain structure in thin Co film on NiO substrate Non Resonant X-Ray Scattering Relative Intensity: 1 Relative Intensity: (hn / mc2)2 hn ~ 10 keV, mc2 = 500 keV Fe metal – L edge Kortright and Kim, Phys. Rev. B 62, 12216 (2000) Resonant Magnetic Soft X-ray Scattering e’ Fe e M I n exp( i q rn ) fn charge 2 magnetic -XMCD fn = e' e Fn(0) - i (e' e) Mn Fn(1) where Fn(i) are complex = f1 + i f2 Note: at resonance f1 = 0 Kortright and Kim, Phys. Rev. B 62, 12216 (2000) Incoherent vs. Coherent X-Ray Scattering Small Angle Scattering -40 40 -20 0 20 scattering vector q (mm-1) Coherence length larger than domains, but smaller than illuminated area information about domain statistics 20 0 -20 -40 40 log (intensity) -40 -20 0 20 40 scattering vector q (mm-1) Coherence length larger than illuminated area -40 40 -20 0 20 scattering vector q (mm-1) Speckle true information about domain structure 20 0 -20 -40 40 log (intensity) -40 -20 0 20 scattering vector q (mm-1) 40 Present Pump/Probe Experiments Laser pulse • Pump: Laser 50 ps • Probe: delayed photon pulse • Vary the delay between laser and xray pulses 330 ns X-Ray pulse Can also produce current pulses Development of High Energy Physics and X-Ray Sources -- From storage rings to linacs -- SR HEP Storage rings Single pass linear colliders Single pass linacs Free electron lasers (FELs) Energy recovery linacs (ERLs) X-Ray Brightness and Pulse Length • X-ray brightness determined by electron beam brightness • X-ray pulse length determined by electron beam pulse length Storage ring Emittance and bunch length are result of an equilibrium typical numbers: 2 nm rad, 50 psec Linac Normalized emittance is determined by gun Bunch length is determined by compression typical numbers: 0.03 nm rad, 100 fs Linac beam can be much brighter and pulses much shorter – at cost of “jitter” • SASE gives 106 intensity gain over spontaneous emission l • FELs can produce ultrafast pulses (of order 100 fs) LINAC COHERENT LIGHT SOURCE 0 Km 2 Km 3 Km Concepts of the LCLS: Based on single pass free electron laser (FEL) Uses high energy linac (~15 GeV) to provide compressed electron beam to long undulator(s) (~120 m) – 200 fs or less Based on SASE physics to produce 800-8,000eV (up to 24KeV in 3rd harmonic) radiation - 1012 photon/shot Analogous in concept to XFEL of TESLA project at DESY Planned operation starting in 2008 From Molecules to Solids: Ultra-fast Phenomena Note in quantum regime: 1 eV corresponds to fluctuation time of 4 fs Chemistry & Biology: H2OOH + H about 10 fs time depends on mass and size Fundamental atomic and molecular reaction and dissociation processes H Condensed Matter: S typical vibrational period is 100 fs Speed of sound is 100 fs / Å - coherent acoustic phonons 90o spin precession time 10 ps for H = 1 Tesla Fundamental motions of charge and spin on the nanoscale (atomic – 100nm size) X-Ray Photon Correlation Spectroscopy Using Split Pulse In picoseconds - nanoseconds range: Uses high peak brilliance sample splitter transversely coherent X-ray pulse from LCLS variable delay t Contrast 10 ps 3mm Analyze contrast as f(delay time) t sum of speckle patterns from prompt and delayed pulses recorded on CCD I(Q,t) Single shot Imaging by Coherent X-Ray Diffraction Phase problem can be solved by “oversampling” speckle image Transmission X-ray Microscope Reconstruction from Speckle Intensities 5 mm (different areas) S. Eisebitt, M. Lörgen, J. Lüning, J. Stöhr, W. Eberhardt, E. Fullerton (unpublished) Spin Block Fluctuations around Critical Temperature Magnetization Tc Temperature t = (T-Tc) / Tc T < Tc T Tc T > Tc Structural Studies on Single Particles and Biomolecules Conventional method: x-ray diffraction from crystal Proposed method: diffuse x-ray scattering from single protein molecule Neutze, Wouts, van der Spoel, Weckert, Hajdu Nature 406, 752-757 (2000) Lysozyme Calculated scattering pattern from lysozyme molecule Implementation limited by radiation damage: In crystals limit to damage tolerance is about 200 x-ray photons/Å2 For single protein molecules need about 1010 x-ray photons/Å2 (for 2Å resolution) X-Ray Diffraction from a Single Molecules A bright idea: Use ultra-short, intense x-ray pulse to produce scattering pattern before molecule explodes Just before LCLS pulse Just after pulse Long after pulse The million dollar question: Can we produce an x-ray pulse that is short enough? intense enough? Summary X-FELs will deliver: unprecedented brightness and femtosecond pulses Understanding of laser physics and technology well founded FELs promise to be extraordinary scientific tools Applications in many areas: chemistry, biology, plasma physics, atomic physics, condensed matter physics The End