XAS: X-ray Absorption Spectroscopy - University of...

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XAS: X-ray AbsorptionSpectroscopy

Hwo-Shuenn Sheu

[email protected], Taiwan

Malaya University, 2011/12/14-5

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outline

•Basic principles for XAS•Experimental setup for XAS•Applications

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A

bsor

ptio

n

Photon energy(eV)

The X-ray Absorption Coefficient: μ

I = I0e−μt

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X-ray Absorption

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Why need SR X-ray sources?

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**

*

RgDsMtHsBhSgDbRfLrRaFr

RnAtPoBiPbTlHgAuPtIrOsReWTaHfLuBaCs

XeITeSbSnInCdAgPdRhRuTcMoNbZrYSrRb

KrBrSeAsGeGaZnCuNiCoFeMnCrVTiScCaK

ArClSPSiAlMgNa

NeFONCBBeLi

HeH

**

*

NoMdFmEsCfBkCmAmPuNpUPaThAc

YbTmErHoDyTbGdEuSmPmNdPrCeLa

XAS accessible elements

XANES only; EXAFS hardish; K-edgeEXAFS; L3-edge EXAFS; L3/K-edgeEXAFS

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X-ray Absorption Basic Principles:

•NEXAFS: near edge x-ray absorptionfine stuture

•XANES: x-ray absorption near edgespectroscopy

•EXAFS: extended x-ray absorption finestructureEXAFS

XANES

x

X-ray photon energy (keV)

-Ge0.0

0.4

0.8

1.2

11 11.5 12

Pre-edge

-20 –50eV

50 –1000eV

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X-ray absorption spectroscopy

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The interference of the outgoing and backscatteredphotoelectron wave

0.0

0.4

0.8

1.2

11 11.5 12

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From Matthew Newville

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Excursion: Wave-particle dualism

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The EXAFS formula: quantitative information

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Structure parameters extracted from EXAFS

R

N

Z

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Experimental setup for XAS

tII

x 0lnTransmission mode

Fluorescence mode x = If / I0

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XAS Beamline (BL17C1) at NSRRC

I0It

Iref

sample

Dr. Jyh Fu Lee

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Fluorescent (Lytle & 13 element array) detector

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Transmission mode (a) and fluorescent mode (b)

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Applications

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414 415

Double excitations

(c)

(c) Double excitations in the N2 spectrum Rydberg associated to the N 1s1g* transition.

(a)

400 401 402

N 1s1g*

(a) 8 vibrational levels observed in the absorpttion spectrum: N 1s1g*

Abs

orpt

ion

Inte

nsity

(arb

.Uni

ts)

406 407 408 409 410Photon Energy (eV)

(b)N 1sRydberg series

1

3

2

4

3

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78

9

10

1112 13

(b) N 1sRydberg series

K-shell photoabsorption of N2 moleculeC.T. Chen and F. Sette, Phys. Rev. A 40 (1989)

K-shell photoabsorption of gas-phase N2

Abs

orpt

ion

Inte

nsity

(arb

.uni

ts)

N 1s 1g*

N 1s Rydberg series

Doubleexcitations

Shaperesonance

x10

400 405 410 415 420Photon energy (eV)

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XANESChemical information: oxidation state

Oxidation Numbers (formalvalences)I Cu2OII CuOIII KCuO2

Higher transitions energy areexpected for higher valencestates.

KCuO2

CuOCu2O

Cu

E (eV)

8970 89900

0.5

1

Y-Ba-Cu-O

(J.B. Boyce et al. Phys. Rev. B 1987)

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Pt L3 and L2 edge XANES

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“White line”reflects the d-orbital occupancy

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“White line”reflects oxidation state

Higher oxidation state

More empty d-orbitals

More intense white line

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“Pre edge”reflect local coordination symmetry

Td

Oh

(tetrahedral)

(tetrahedral)

(spinel)

(octahedral)

(octahedral)

Co K-edge

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EXAFS of LiCoO2 powder

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EXAFS of LiCoO2 during charging cycled

Staticordering

Thermalvibration

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Use EXAFS to probe coordination environment:Na(Co0.99Mn0.01)O2

Similar EXAFSspectrum indicateMn and Co are insimilar chemicalenvironment.

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Ru/Cu core shell structure characterization

Ru/SiO2

Ru-Cu/SiO2

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Cu/SiO2

Cu-Ru/SiO2

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Fresh FreshOxidized Oxidized

Ru Cu

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High pressure x-ray absorption spectroscopy

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Pressure-induced structural distortion of TbMnO3: Acombined XRD and XAS study

Physical Review B 79, 165110 2009

XRD data and the enhanced intensity of the whiteline and the shifted absorption threshold of Mn K-edge spectra enabled observation of a reducedlocal Jahn-Teller distortion of Mn sites within MnO6octahedra in TbMnO3 with increasing pressure.These provide spectral evidence for pressure-induced bandwidth broadening for mangnites.

a

b1.889Å

2.243Å

145.7 º

Mn(1)

Mn(2)

Mn(1)

Mn(2)

J`

J

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Horse tail hair has beenmeasured to grow between 390and 1260 micrometers per day(compared to ca. 330 micrometersfor human head hair).[7] Thegrowth of mane hair may bewithin this range, in which case a500 micrometer segmentwould correspond to betweenapproximately 10–30 hours ofgrowth.

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Determination of Arsenic Poisoning and Metabolism in Hair bySynchrotron Radiation: The Case of Phar Lap**

Ivan M. Kempson* and Dermot A. Henry Angew. Chem. Int. Ed. 2010, 49, 4237 –4240

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Photo-Induced Magnetization in Co-Fe Prussian Blue Magnets

•Structural disorder dictated by

composition/processing

•PIM initially observed in

K0.2Co1.4[Fe(CN)6]·6.9H2O

O.Sato et al., Science 272, 704 (1996)

- Ferrimagnetic ordering below ~16 K

- Magnetization increase obtained by red light

- Photoinduced state has lifetime >10 5 s at low T

- Effect reversed by blue light, heating

K+ is interstitial

Fe

Co

C

N

Defect(missing Fe)

KxCoy[Fe(CN)6]˙zH2O

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Photoinduced magnetismin

RbjCok[Fe(CN)6]l.nH2O

DiamagneticFeII-CN-CoIII

FerrimagneticFeIII-CN-CoII

Electron transfer andspin crossover

h

DiamagneticFeII-CN-CoIII

FerrimagneticFeIII-CN-CoII

Electron transfer andspin crossover

h

-10 0 10 20 30 40 50-10

-5

0

5

10

Mag

net

izat

ion

Ch

ang

e(x

105

emu

-G)

Magnetic fieldparallel

Magnetic fieldperpendicular



Lig

ht

Off

Light On

Time (min)

-10 0 10 20 30 40 50-10

-5

0

5

10

Mag

net

izat

ion

Ch

ang

e(x

105

emu

-G)





Lig

ht

Off

Light On

Time (min)

The magnetism of a nanoscale film of amolecule-based magnet is controlled byboth light and orientation.

RbjCok[Fe(CN)6]l.nH2O

x5

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XRD and XANES of KxCoy[Fe(CN)6]Synthesized in Various Concentration of KCl

14.0 14.2 14.4 14.6 14.8 15.0 15.2 15.4 15.6 15.8 16.0

0.0

5.0x103

1.0x104

1.5x104

2.0x104

0 M KCl

0.1 M KCl

0.5 M KCl

1.0 M KCl

Cou

nts

(a.u

.)

2(degree)

(2 0 0) reflection

7700 7710 7720 7730 7740 7750 7760 7770 7780

0

1

2

3

4

1M KCl

0.5M KCl

0.1M KCl

0M KCl

Abs

orpt

ion

(a.u

.)

Energy (eV)

XANES of Co K-edge

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X-ray Powder Diffraction of KxCoy[Fe(CN) 6]Synthesized in 0.1 M KCl Solution

10 20 30 40 50 60 70 80 90

-2000

0

2000

4000

6000

8000

10000

120005/13/00

Space group: F m 3 mPI : a=10.2787(1)PII : a= 9.9851(6)wRp=0.050Rp=0.033X=0.8529

PI : 1.987(5) 1.140 2.012(5)PII: 1.86(3) 1.140 1.996(3)

Co N C Fe

coun

ts(a

.u.)

2(degree)

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Water- desorption of KxCoy[Fe(CN)6].nH2OXANES of Co K-edge

7700 7710 7720 7730 7740 7750 77600.0

0.5

1.0

1.5

2.0

Pre-edge14K to RT in Vacuum

14K to RT then in air

10-3 torr (30min)

RT in air

Abs

orpt

ion

(a.u

.)

Energy (eV)

vacuum

7700 7710 7720 7730 7740 7750

0.5

1.0

1.5

2.0

2.5Co K-edge25 C

45 C55 C65 C75 C85 C95 C

105 C125 C

Abs

orpt

ion

Energy (eV)

Heating

7700 7710 7720 7730 7740 7750 77600.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

7%11%18%19%32%42%

Abs

orpt

ion

Energy (eV)

Humidity

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Lytle Detector

APD Cryostat

Xe Lamp

Light irradiation of Co, Fe Prussian Blue magnets

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XANES of Co K-edge: In-situ Xe-lamp Red light(650±40nm) illuminated at 15K

• The Co 3+ become Co 2+

during red lightillumination at 15K andsaturation in 20 min.

• The K-edge of Fe alsoshow significant changeduring the irradiation.

7700 7710 7720 7730 7740 7750 77600.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Co-Kedge

0 min1 min

4.5 min11 min20 min27 min30 min

Abs

orpt

ion

Energy (eV)

7100 7110 7120 7130 7140 7150

0.00

0.05

0.10

0.15

0.20

0 min38 min42 min45 min

7129.0 7129.5 7130.0 7130.5 7131.0 7131.5 7132.0 7132.5 7133.00.160

0.165

0.170

0.175

0.180

Fe K-edge

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Yu Wang, et al J. Am. Chem. Soc. 2000, 122(24), 5742-5747

X-ray Absorption Spectroscopic Studies on Light-InducedExcited Spin State Trapping of an Fe(II) Complex

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K-edge L-edge

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Acknowledgement

•Prof. Yu Wang ( NTU)•Prof. Bing-Joe Hwang (NTUST)•Dr. Jyh-Fu Lee (NSRRC)•Dr. Ting-Shan Chan (NSRRC)•Dr. Jin-Ming Chen (NSRRC)

Thank you for your attention!

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