John Bargar Senior Scientist June 28, 2011

1. SSRL Synchrotron X-Ray Absorption Spectroscopy Summer School (6th annual)June 28 - July 1, 2011 Welcome! John Bargar Senior Scientist June 28, 2011

2. Overview: “The view from 20,000 feet” • What is X-ray Absorption Spectroscopy? • What is Synchrotron Radiation? • Beam lines at SSRL • A little history • The rest of the story (workshop outline)

3. What is x-ray absorption spectroscopy?

4. Electromagnetic Radiation - How It Relates to the World We Know Synchrotron radiation is used for experiments typically over this region

5. Electromagnetic Radiation - How It Relates to the World We Know XAS Synchrotron radiation is used for experiments typically over this region

6. Aperture- defining slits Aperture- defining slits pre-detector pre detector Sample Ionization chamber Fluorescence Detector Energy-dispersive Fluorescence Detector absorption detectors absorption detectors The Basic XAS Experiment SSRL BL 11-2

7. XANES / NEXAFS Oxidation state, Molecular structure, Electronic structure. EXAFS Quantitative Local Structure. Fe2O3 2.32Å Cr(III) 2.46Å 2.90 Å 3.43 Å Cr(VI) XAS: What you get out of the measurement: Basic Experiment : =XANES (X-ay Absorption Near Edge Structure) =NEXAFS (Near Edge X ray Absorption Fine Structure) (EXAFS = Extended X ray Absorption Fine Structure) Eb Core electron binding energy, Eb

8. Key point: XAS is element specific λ = 2 Å λ = 1.5 Å X-ray absorption K-edges of some first-row transition metal foils.

9. What Makes Synchrotron Radiation (SR) so Useful? Wide energy spectrum: SR is emitted with a wide range of energies High brightness: SR is extremely intense (hundreds of thousands of times higher than conventional x-ray tubes) Highly polarized and short pulses: SR is emitted in very short pulses, typically less that a nano-second (a billionth of a second) SR offers many characteristics of visible lasers but into the x-ray regime!

10. Normalize to edge step start stop Normalized Data 1.0 k3-weighted EXAFS EXAFS XAS: Basic Data Reduction EXAFS XANES

11. What is synchrotron radiation?

12. “The Crab Nebula, or Messier 1, is one of the most spectacular and intensively studied objects in the sky. It is the remnant of a supernova in AD 1054, observed as a "guest star" by the Chinese in today's constellation Taurus. It is among the brightest remnants across a broad wavelength spectrum. The Crab Nebula is probably the best-known synchrotron emission nebula. The synchrotron light is what is primarily seen in the 2MASS image…. “ http://www.ipac.caltech.edu/2mass/gallery/images_snrs.html Synchrotron Radiation - What is it? • First terrestrial sources were cyclic - electron synchrotrons developed for high-energy physics (HEP) research (1940-1970) and used parasitically as light sources with variable intensity and variable spectrum • 1960s began the development of storage rings – again for HEP – and used mostly parasitically as light sources, demonstrating the advantages of constant intensity and constant spectrum – the “First” Generation Visible Synchrotron Light

13. Synchrotron Radiation - How is it Practically Produced and Used for Research? the storage ring circulates electrons and where their path is bent - synchrotron radiation is produced klystrons generate high power radiowaves to sustain electron acceleration, replenishing energy lost to synchrotron radiation electron gun produces electrons beam lines transport radiation into “hutches” where instrumentation is available for experiments special “wiggler” insertion devices used to generate x-rays accelerator/booster accelerate e- which are transported to storage ring

15. Bend Magnet Wiggler Undulator What is a Synchrotron? • Synchrotrons spin bunches of electrons accelerated by strong magnetic fields

16. K2 2 lu (1 + ) ~(fundamental) l1 = 2g2 lU + harmonics at higher energy g2 0.95 E2 (GeV) e1 (keV) = K2 lu (cm) (1 + ) 2 K = gq where q is the angle in each pole Bending Magnets and Insertion Devices on Storage Rings Continuous spectrum characterized by ec = critical energy ec(keV) = 0.665 B(T)E2(GeV) e.g.: for B = 2T E = 3GeV ec = 12keV (bending magnet fields are usually lower ~ 1 – 1.5T) bending magnet - a “sweeping searchlight” wiggler - incoherent superposition Quasi-monochromatic spectrum with peaks at lower energy than a wiggler undulator - coherent interference

17. One of the First SR Data Sets Ever… ca. 1974-1975 In Laboratory: 2 weeks! SSRL, 1972: 20 mins! S. Doniach, K. Hodgson, I. Lindau, P. Pianetta, H. Winick, J. Synch. Rad. 4, 380 (1997)

18. XFELs - another >10 billion in peak What Makes Synchrotron Radiation (SR) so Useful? Wide energy spectrum: SR is emitted with a wide range of energies High brightness: SR is extremely intense (hundreds of thousands of times higher than conventional x-ray tubes) Highly polarized and short pulses: SR is emitted in very short pulses, typically less that a nano-second (a billionth of a second) ~ 1 trillion SR offers many characteristics of visible lasers but into the x-ray regime!

19. Synchrotron Radiation - Basic Properties Pulsed time structure

20. XFELs - another >10 billion in peak What Makes Synchrotron Radiation (SR) so Useful? Wide energy spectrum: SR is emitted with a wide range of energies High brightness: SR is extremely intense (hundreds of thousands of times higher than conventional x-ray tubes) Highly polarized and short pulses: SR is emitted in very short pulses, typically less that a nano-second (a billionth of a second) ~ 1 trillion SR offers many characteristics of visible lasers but into the x-ray regime!

21. A Range of X-ray Absorption Spectroscopy Approaches • Polarized single crystal XAS– combined with protein crystallography – electronic information; higher accuracy for metal site structure; radiation-imposed structural changes • Polarized grazing-incidence XASof metals at oriented surfaces and interfaces. • MicroXAS imagingfor elemental mapping, electronic and metric structure for speciation and ultimately functional understanding – at beam size and raster density adjusted to biological specimen and study requirement • High-throughput biological XAS for structural genomics application – requires efforts in automation • High-energy resolution techniques with x-ray emission component – selective EXAFS, resonant inelastic scattering (RIXS), non-resonant x-ray Raman scattering

22. Beam lines at SSRL

23. SSRL XAS Beam Lines “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se) Bio-XAS 9-3 7-3

24. SSRL XAS Beam Lines “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se) Bio-XAS 9-3 7-3 4-1 Grazing incidence Biogeochemistry and Materials “hard x-ray” XAS: E.g.: Mn, As, Pb, Hg, U, Pu, Ag, Te, 11-2

25. SSRL XAS Beam Lines “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se) Bio-XAS 9-3 7-3 4-1 Grazing incidence Biogeochemistry and Materials “hard x-ray” XAS: E.g.: Mn, As, Pb, Hg, U, Pu, Ag, Te, 11-2 14-3 4-3 “Soft” x-ray XAS: P, S, Cl, Ca, V, Cr

26. SSRL XAS Beam Lines 10-2 “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se) Bio-XAS 9-3 7-3 Micro-XAS, imaging 2-3 X-ray microscopy RIXS, High-resolution emission XAS 6-2 4-1 Grazing incidence Biogeochemistry and Materials “hard x-ray” XAS: E.g.: Mn, As, Pb, Hg, U, Pu, Ag, Te, 11-2 14-3 4-3 “Soft” x-ray XAS: P, S, Cl, Ca, V, Cr

27. Beamlines - Delivering the Photons to the Experimenters - What are they? monochromator user control area mirror storage ring e- beam photon beam BL front end hutch Typical wiggler beam line with multiple (3) branches

28. A little history…

29. SSRP Bldg 120 – the beginning - 1973 SSRP Bldg 131 – a major expansion of the hall SPEAR with Bldg 120 – before 131 Expanding Bldg 120 for BL9 and labs Was not always like this… In all – the experimental hall around SPEAR has had 8 additions since the initial construction in 1973-74

30. First SSRL “Hutch” 1973

31. ..and the First EXAFS “Hutch” on SSRL BL1-5

32. Linac-driven Light Sources - Toward the 4th Generation Brightness and Pulse Length in Electron-based X-ray generation • X-ray brightness determined by electron beam brightness • X-ray pulse length determined by electron beam pulse length Storage ring (“conventional synchrotron radiation”) Emittance and bunch length are result of an equilibrium Typical numbers: 2 nm rad, 50 psec Linac (source for X-ray FEL or ERL) Normalized emittance is determined by electron gun Bunch length is determined by electron compression Typical numbers: 0.03 nm rad, 100 fs or shorter Linac beam can be much brighter and pulses much shorter! – at cost of “jitter”- and provides necessary characteristics for ERLs or x-ray FEL generation

33. Linac-driven Light Sources - Toward the 4th Generation Storage Ring vs. Linac-based Sources

34. XFELs - another >10 billion in peak QUIZ TIME: What Makes Synchrotron Radiation (SR) so Useful? 1. _____________ 2. ______________ 3. ______________ ~ 1 trillion

35. XFELs - another >10 billion in peak What Makes Synchrotron Radiation (SR) so Useful? Wide energy spectrum: SR is emitted with a wide range of energies High brightness: SR is extremely intense (hundreds of thousands of times higher than conventional x-ray tubes) Highly polarized and short pulses: SR is emitted in very short pulses, typically less that a nano-second (a billionth of a second) ~ 1 trillion

36. The Rest of The Story • TUESDAY: Fundamentals • WEDNESDAY: Data Acqusition • THURSDAY: Basics of data analysis • THURSDAY NIGHT: BBQ! • FRIDAY: Advanced data analysis