Transcript “hard x-ray” XAS - Stanford Synchrotron Radiation Lightsource

SSRL Synchrotron X-Ray Absorption
Spectroscopy Summer School (6th annual)
June 28 - July 1, 2011
15
U LIII edge
Bacteria
10
3
FT of k (k)
5
0
-5
data at 298 K
fit
-10
-15
0
1
2
3
4
r (Å)
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
• A little history
• The rest of the story (workshop outline)
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
XAS
Synchrotron radiation is
used for experiments
typically over this region
The Basic XAS Experiment
Aperturedefining slits
pre-detector
pre detector
SSRL BL 11-2
Ionization chamber Sample
Fluorescence Detector
absorption
detectors
Energydispersive
Fluorescence
Detector
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
XANES / NEXAFS
Oxidation state,
Molecular structure,
Electronic structure.
EXAFS
Quantitative Local Structure.
Fe2O3
Cr(III)
0.8
0.6
0.4
1
0.2
0
A b s o rb a n c e
A b s o rb a n c e
1
Cr(VI)
0.8
0.6
Core electron binding
energy, Eb
0.4
0.2
0
5980
6000
6020
X-ray Energy (eV)
6040
3.43 Å
Key point: XAS is element specific
λ=2Å
λ = 1.5 Å
X-ray absorption K-edges of some first-row transition metal foils.
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
start
stop
Normalized Data
1.0
3-weighted EXAFS
kEXAFS
EXAFS
XANES
What is synchrotron radiation?
Synchrotron Radiation - What is it?
•
First terrestrial sources were
cyclic - electron synchrotrons
developed for high-energy
physics (HEP) research (19401970) 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
“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 - 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
What is a Synchrotron?
Bend Magnet
Wiggler
•Synchrotrons spin
bunches of electrons
accelerated by strong
magnetic fields
Undulator
Bending Magnets and Insertion Devices on Storage Rings
Continuous spectrum
characterized by ec = critical
energy
bending magnet - a “sweeping searchlight”
ec(keV) = 0.665 B(T)E2(GeV)
e.g.: for B = 2T E = 3GeV ec
= 12keV
wiggler - incoherent superposition
(bending magnet fields are
usually lower ~ 1 – 1.5T)
Quasi-monochromatic spectrum with
peaks at lower energy than a wiggler
l1 =
lu
2g2
(1 +
lU
K2
)~
(fundamental)
2
g2
+ harmonics at higher energy
undulator - coherent interference
0.95 E2 (GeV)
2
lu (cm) (1 + K )
2
K = gq where q is the angle in each pole
e1 (keV) =
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)
XFELs another
>10 billion
in peak
~ 1 trillion
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!
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)
XFELs another
>10 billion
in peak
~ 1 trillion
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!
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), nonresonant x-ray Raman scattering
Beam lines at SSRL
SSRL XAS Beam Lines
7-3
Bio-XAS
9-3
“Hard x-ray”: 1st, 2nd-row
transition metals, P-block
elements (As, Se)
SSRL XAS Beam Lines
7-3
Bio-XAS
“Hard x-ray”: 1st, 2nd-row
transition metals, P-block
elements (As, Se)
9-3
4-1
11-2
Grazing incidence
Biogeochemistry
and Materials
“hard x-ray” XAS:
E.g.: Mn, As, Pb,
Hg, U, Pu, Ag, Te,
SSRL XAS Beam Lines
7-3
Bio-XAS
“Hard x-ray”: 1st, 2nd-row
transition metals, P-block
elements (As, Se)
9-3
4-1
11-2
14-3
“Soft” x-ray XAS:
P, S, Cl, Ca, V, Cr
Grazing incidence
4-3
Biogeochemistry
and Materials
“hard x-ray” XAS:
E.g.: Mn, As, Pb,
Hg, U, Pu, Ag, Te,
SSRL XAS Beam Lines
10-2
7-3
Micro-XAS,
imaging
Bio-XAS
“Hard x-ray”: 1st, 2nd-row
transition metals, P-block
elements (As, Se)
9-3
2-3
6-2
4-1
11-2
14-3
“Soft” x-ray XAS:
P, S, Cl, Ca, V, Cr
X-ray microscopy
RIXS, Highresolution emission
XAS
Grazing incidence
4-3
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?
user control area
monochromator
mirror
storage ring
e- beam
photon beam
BL front end
hutch
Typical wiggler beam line with multiple (3) branches
A little history…
Was not always like this…
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
In all – the experimental hall around SPEAR has had 8 additions since the initial construction in 1973-74
First SSRL “Hutch” 1973
..and the First EXAFS “Hutch” on SSRL BL1-5
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
Linac-driven Light Sources - Toward the 4th Generation
Storage Ring vs. Linac-based Sources
QUIZ TIME:
What Makes Synchrotron Radiation (SR) so Useful?
1. _____________
XFELs another
>10 billion
in peak
2. ______________
~ 1 trillion
3. ______________
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)
XFELs another
>10 billion
in peak
~ 1 trillion
The Rest of The Story
• TUESDAY: Fundamentals
• WEDNESDAY: Data Acqusition
• THURSDAY: Basics of data analysis
• THURSDAY NIGHT: BBQ!
• FRIDAY: Advanced data analysis