John Bargar Senior Scientist June 28, 2011
36
John Bargar John Bargar Senior Senior Scientist Scientist June 28, 2011 June 28, 2011 SSRL Synchrotron X-Ray Absorption Spectroscopy Summer School (6 th annual) June 28 - July 1, 2011 Welcome! 0 1 2 3 4 -15 -10 -5 0 5 10 15 U L III edge data at298 K fit F T of k 3 (k) r (Å ) B acteria
description
SSRL Synchrotron X-Ray Absorption Spectroscopy Summer School (6 th annual) June 28 - July 1, 2011. Welcome!. John Bargar Senior Scientist June 28, 2011. Overview: “The view from 20,000 feet”. What is X-ray Absorption Spectroscopy? What is Synchrotron Radiation? Beam lines at SSRL - PowerPoint PPT Presentation
Transcript of John Bargar Senior Scientist June 28, 2011
John BargarJohn BargarSenior ScientistSenior ScientistJune 28, 2011June 28, 2011
SSRL Synchrotron X-Ray Absorption Spectroscopy Summer School (6th annual)
June 28 - July 1, 2011
Welcome!
0 1 2 3 4-15
-10
-5
0
5
10
15
U LIII
edge
data at 298 K fit
FT o
f k3 (k)
r (Å)
Bacteria
• 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”
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 11-2pre detector
Aperture-defining slits
absorption detectors
Energy-dispersive Fluorescence Detector
Ionization chamberFluorescence Detector
XAS: What you get out of the measurement:
Basic Experiment :
Core electron binding energy, Eb
Eb
2.32Å 2.46Å
3.43 Å
2.90 Å
Fe2O3
EXAFSQuantitative Local Structure.
=XANES (X-ay Absorption Near Edge Structure)=NEXAFS (Near Edge X ray Absorption Fine Structure)
XANES / NEXAFSOxidation state, Molecular structure, Electronic structure.
0
0.2
0.4
0.6
0.8
1
Abs
orba
nce
Cr(III)
0
0.2
0.4
0.6
0.8
1
5980 6000 6020 6040
Abs
orba
nce
X-ray Energy (eV)
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 Å λ = 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
Normalizeto edge step
EXAFS
Normalized Data
1.0
XANES
start stop
EXAFSk3-weighted EXAFS
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…. “ http://www.ipac.caltech.edu/2mass/gallery/images_snrs.html
• 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” GenerationSynchrotron 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) = 0.665 B(T)E2(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
2
U
+ harmonics at higher energy
0.95 E2 (GeV)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. 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)
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
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
2.0
1.5
1.0
0.5
0.06543210
R'()
Co
-10
-5
0
5
10
12108642k (-1)
SSRL XAS Beam Lines
Bio-XAS 9-37-3 “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se)
4-111-2
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 9-37-3 “Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se)
4-1
4-3
11-2
SSRL XAS Beam Lines
Bio-XAS 9-37-3
14-3
“Soft” x-ray XAS:P, S, Cl, Ca, V, Cr
“Hard x-ray”: 1st, 2nd-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,
2-3
4-1
4-3
11-2
SSRL XAS Beam Lines
Micro-XAS, imaging
Bio-XAS 9-37-3
10-2
14-3
“Soft” x-ray XAS:P, S, Cl, Ca, V, Cr
“Hard x-ray”: 1st, 2nd-row transition metals, P-block elements (As, Se)
6-2 X-ray microscopyRIXS, 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 areamirror
monochromator
e- beam
photon beam
hutch
Was not always like this…
SSRP Bldg 120 – the beginning - 1973
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 1973-74
Brightness and Pulse Length in Electron-based X-ray generationBrightness 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 equilibriumTypical 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 compressionTypical numbers: 0.03 nm rad, 100 fs or shorter
Linac-driven Light Sources - Toward the 4th Generation
Storage Ring vs. Linac-based SourcesStorage Ring vs. Linac-based Sources
Linac-driven Light Sources - Toward the 4th 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
