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

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

What is x-ray absorption spectroscopy?

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

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

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

XAS: What you get out of the measurement: Basic Experiment : Core electron binding energy, E b EbEb 2.32Å 2.46Å 3.43 Å 2.90 Å Fe 2 O 3 EXAFS Quantitative Local Structure. =XANES (X-ay Absorption Near Edge Structure) =NEXAFS (Near Edge X ray Absorption Fine Structure) XANES / NEXAFS Oxidation state, Molecular structure, Electronic structure. Cr(III) Cr(VI) (EXAFS = Extended X ray Absorption Fine Structure)

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

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!

XAS: Basic Data Reduction Normalize to edge step EXAFS Normalized Data 1.0 XANES start stop EXAFS k 3 -weighted EXAFS

What is synchrotron radiation?

Synchrotron Radiation - What is it? “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…. “ First terrestrial sources were cyclic - electron synchrotrons developed for high-energy physics (HEP) research ( ) 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 Synchrotron Light Visible

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

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

Continuous spectrum characterized by  c = critical energy  c (keV) = B(T)E 2 (GeV) e.g.: for B = 2T E = 3GeV  c = 12keV (bending magnet fields are usually lower ~ 1 – 1.5T) Quasi-monochromatic spectrum with peaks at lower energy than a wiggler  1 (keV) = K =  where  is the angle in each pole 1 = u   (1 + ) ~ (fundamental) KK 22 U + harmonics at higher energy 0.95 E 2 (GeV) KK u (cm) (1 + ) 2 Bending Magnets and Insertion Devices on Storage Rings undulator - coherent interference wiggler - incoherent superposition bending magnet - a “sweeping searchlight”

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

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! XFELs - another >10 billion in peak

Synchrotron Radiation - Basic Properties Pulsed time structure

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! XFELs - another >10 billion in peak

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 XAS of metals at oriented surfaces and interfaces. MicroXAS imaging for 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

Beam lines at SSRL

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

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

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

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

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

A little history…

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

First SSRL “Hutch” 1973

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

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 beam can be much brighter and pulses much shorter! – at cost of “jitter”- and provides necessary characteristics for ERLs or x-ray FEL generation 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-driven Light Sources - Toward the 4 th Generation

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

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

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