XAS detection techniques XAS spectral shape 1s XAS - - PowerPoint PPT Presentation

▶
xas detection techniques
SMART_READER_LITE
LIVE PREVIEW

XAS detection techniques XAS spectral shape 1s XAS - - PowerPoint PPT Presentation

Dec 12, 2023 113 likes •636 views

X-ray Absorption Spectroscopy Introduction to XAS XAS detection techniques XAS spectral shape 1s XAS (pre-edges) Overview of programs Overview of spectroscopies X-ray Absorption Spectroscopy Element specific

slide-1
SLIDE 1
  • Introduction to XAS
  • XAS detection techniques
  • XAS spectral shape
  • 1s XAS (pre-edges)
  • Overview of programs
  • Overview of spectroscopies

X-ray Absorption Spectroscopy

slide-2
SLIDE 2
  • Element specific
  • Sensitive to low concentrations
  • Applicable under extreme conditions
  • SPACE: Combination with x-ray microscopy
  • TIME: femtosecond XAS
  • RESONANCE: RIXS, RPES, RAES, R scat.

X-ray Absorption Spectroscopy

slide-3
SLIDE 3

 − −

   

i f

E E i f f XAS

r e I

2

ˆ ~

Excitations of core electrons to empty states The XAS spectra are given by the Fermi Golden Rule

XAS: spectral shape

exciton edge jump

slide-4
SLIDE 4

The photon moves towards the atom

X-ray Absorption Spectroscopy

slide-5
SLIDE 5

The photon meets an electron and is annihilated

X-ray Absorption Spectroscopy

slide-6
SLIDE 6

The electron gains the energy of the photon and is turned into a blue electron.

X-ray Absorption Spectroscopy

slide-7
SLIDE 7

The blue electron (feeling lonely) leaves the atom and scatters of neighbors

  • r escapes from the sample

X-ray Absorption Spectroscopy

slide-8
SLIDE 8

The probability of photon annihilation determines the intensity of the transmitted photon beam

I0 I Ek

X-ray Absorption Spectroscopy

slide-9
SLIDE 9

X-ray absorption

X-ray Absorption Spectroscopy

  • Excitation of 2p to 3d state
  • Lifetime of excitation is ~20 fs
slide-10
SLIDE 10

X-ray absorption & x-ray emission

X-ray Absorption Spectroscopy

  • Decay of 3d or 3s electron to 2p core state
  • X-ray emission
slide-11
SLIDE 11

X-ray absorption & Auger

  • Decay of 3d/3p/3s electron to 2p core state
  • Energy used to excite a 3d/3p/3s electron
  • Auger electron spectroscopy

X-ray Absorption Spectroscopy

slide-12
SLIDE 12

X-ray Absorption Spectroscopy

slide-13
SLIDE 13

XAS: detection techniques

slide-14
SLIDE 14

I Entrance slits II Monochromator IIIExit slits IV Ionisation chamber V Sample VI Ionisation chamber VII Reference material VIII Ionisation chamber

X-ray absorption beamline (transmission)

XAS: detection techniques

slide-15
SLIDE 15

Pinhole effect in transmission

XAS: detection techniques

slide-16
SLIDE 16

X-ray penetration lengths & electron escape depths

1000 nm

(CXRO, but 20 nm for L edges)

1 nm

XAS: detection techniques

slide-17
SLIDE 17

Use decay channels as detector

XAS: detection techniques

slide-18
SLIDE 18

Fluorescence Yield

B FY

E E I    +  ) ( ) (

XAS: detection techniques

slide-19
SLIDE 19

Transmission (pinhole, saturation > thin samples) Electron Yield (surface sensitive) Fluorescence Yield (saturation > dilute samples; L edges are intrinsically distorted)

XAS: detection techniques

slide-20
SLIDE 20

➢ Interpretation of spectral shapes XAS: spectral shape

slide-21
SLIDE 21

Iron 1s XAS

Metal K edges

exciton edge jump

slide-22
SLIDE 22

 − −

   

i f

E E i f f XAS

r e I

2

ˆ ~

Excitations of core electrons to empty states The XAS spectra are given by the Fermi Golden Rule

XAS: spectral shape

exciton edge jump

slide-23
SLIDE 23

Fermi Golden Rule  Excitations to empty states as calculated by DFT

symmetry site XAS

M I

, 2

~   

O 1s

XAS: spectral shape (O 1s)

X

slide-24
SLIDE 24

2p 2s

  • Phys. Rev. B.40, 5715 (1989)

XAS: spectral shape (O 1s)

slide-25
SLIDE 25
  • Phys. Rev. B.40, 5715 (1989); 48, 2074 (1993)
  • xygen 1s > p DOS

XAS: spectral shape (O 1s)

slide-26
SLIDE 26
  • Phys. Rev. B. 40, 5715 (1989); 48, 2074 (1993)

XAS: spectral shape (O 1s)

slide-27
SLIDE 27
  • Final State Rule:

Spectral shape of XAS looks like final state DOS TiSi2

  • Phys. Rev. B. 41, 11899 (1991)

XAS: spectral shape

slide-28
SLIDE 28

Iron 1s XAS

2p XAS of transition metal ions

[Phys. Rev. B. 42, 5459 (1990)]

exciton edge jump

2p > s,d DOS 2p > 3d (3d5 > 2p53d6, self screened)

X

slide-29
SLIDE 29

2p3/2 2p1/2 Overlap of core and valence wave functions

→ Single Particle model breaks down

3d

<2p3d|1/r|2p3d>

XAS: multiplet effects

  • Phys. Rev. B. 42, 5459 (1990)

XAS: spectral shape

slide-30
SLIDE 30

1-particle: 1s edges (DFT + core hole +U) many-particle:

  • pen shell systems

(CTM4XAS)

Interpretation of XAS

XAS: spectral shape

slide-31
SLIDE 31

XAS 1s (TD)-DFT pre-edge

  • f 3d system

2p, 3p, 3d, 4d multiplets

XAS: spectral shape

slide-32
SLIDE 32

Fe 4p

  • Fe 3d

O 2p

5

O 2s

20

Fe 3p

50 Fe 3s 85 O 1s 530 Fe 2p 700 Fe 2s 800 Fe 1s 7115

X-ray absorption of a solid

Pre-edges structures in 1s XAS

slide-33
SLIDE 33

3dN 4p0

1s13dN+14p0

pre-edge edge

1s13dN4p1

Pre-edges structures in 1s XAS

exciton edge jump

slide-34
SLIDE 34

3dN 4p0

1s13dN+14p0

pre-edge edge

1s13dN4p1

[Cabaret et al. j. Synchrot. Rad. 6, 258 (1999)]

Pre-edges structures in 1s XAS

slide-35
SLIDE 35

3dN 4p0

1s13dN+14p0

pre-edge edge

1s13dN4p1

[J. Phys. Cond. Matt. 21, 104207 (2009)]

Pre-edges structures in 1s XAS

slide-36
SLIDE 36

XAS 1s (TD)-DFT pre-edge

  • f 3d system

2p, 3p, 3d, 4d multiplets

XAS: spectral shape

slide-37
SLIDE 37

Multiplet calculations

Calculated for an atom/ion ➢ Valence and core hole spin-orbit coupling ➢ Core hole – valence hole ‘multiplet’ interaction. Comparison with experiment ➢ Core hole potential and lifetime ➢ Local symmetry (crystal field) ➢ Spin-spin interactions (molecular field) ➢ Core hole screening effects (charge transfer) Neglected ➢ The coupling of core hole excitations to vibrations

slide-38
SLIDE 38

(available) 2p XAS semi-empirical codes

➢ Thole .cowan-racah-bander ➢ Haverkort .quanty ➢ Tanaka ➢ Van Veenendaal

slide-39
SLIDE 39

(available) 2p XAS Interfaces

➢ Thole > CTM4XAS, missing, ttmult(s) ➢ Tanaka ➢ Haverkort > Crispy, CTM4XAS6, Quanty4RIXS ➢ Van Veenendaal > Xclaim

slide-40
SLIDE 40

2p XAS first-principle codes

➢ Band structure multiplet (Haverkort, Green, Hariki) ➢ Cluster DFT multiplet (Ikeno, Ramanantoanina, Delley) ➢ Restricted Active Space CI (Odelius, Kuhn) ➢ Restricted Open-shell CI (Neese) ➢ Time-Dependent DFT (Joly) ➢ Bethe-Salpeter (Rehr, Shirley) ➢ Multi-channel Multiple-scattering (Kruger)

slide-41
SLIDE 41

Quanty first principle multiplet calculations

Calculated for a solid ➢ The core hole spin-orbit coupling ➢ The core hole – valence hole ‘multiplet’ interaction. ➢ The core hole induced screening effects [except U] ➢ The core hole lifetime Comparison with experiment ➢ The core hole potential Neglected ➢ The coupling of core hole excitations to vibrations

slide-42
SLIDE 42
slide-43
SLIDE 43

Iron 1s XAS

Overview

  • XAS
  • MCD
  • XPS
  • RIXS
  • Ground state
slide-44
SLIDE 44

Iron 1s XAS

Overview

exciton edge jump

slide-45
SLIDE 45

Iron 1s XAS

2p XAS

X

I(w)

Γ2p= 0.2 eV

slide-46
SLIDE 46

Iron 1s XAS

2p XMCD

X

I+(w)- I-(w)

Γ2p= 0.2 eV

Left and right polarized x-rays

slide-47
SLIDE 47

Iron 1s XAS

2p XPS

I(Ek)

Γ2p= 0.2 eV

(additional broadening)

slide-48
SLIDE 48

Iron 1s XAS

2p XAS

X

I(w)

Electronic, magnetic, vibrational

slide-49
SLIDE 49

Iron 1s XAS

2p3d RIXS

X

I(w,w’)

Fixed energy loss

Electronic, magnetic, vibrational

Γ3d= 10 meV?

slide-50
SLIDE 50

Iron 1s XAS

2p XPS

slide-51
SLIDE 51

Iron 1s XAS

2p3d fluorescence

I(w’)

Electronic, magnetic, vibrational

Γ2p= 0.2 eV

Fixed emission energy