X-ray Photoelectron Spectroscopy for Chemical Analysis · the field of X-ray spectroscopy.”...

X-ray Photoelectron Spectroscopy

for Chemical Analysis J. ANIBAL BOSCOBOINIK

[email protected]

MSAE E8235x: Selected Topics In Materials Science. Columbia University, Oct 14th 2015

Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) endstation at NSLS-II

Photon Energy: 250 eV to 2000 eV Pressures up to 5 Torr.

Temperatures up to 900 C Capillary tube into Mass Spec.

AP-XPS End Station

BS Chemistry San Luis

PhD Chemistry Wisconsin

PostDoc Chemical Physics Berlin

Materials Scientist New York

Who is this guy?

Columbia University, Oct 14th 2015. Anibal Boscoboinik - CFN, Brookhaven Lab

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Anibal Boscoboinik - CFN, Brookhaven Lab

Our Playground

Columbia University, Oct 14th 2015. Anibal Boscoboinik - CFN, Brookhaven Lab 4

What will you learn today?

• X-ray Photoelectron Spectroscopy (XPS)

• Ambient Pressure XPS.

• What you can do with it.

• Some examples.


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• Background

Photoelectric Effect

The photoelectric effect is the observation that many metals emit electrons when light shines upon them. (Hertz 1887)

𝑬 = 𝒉𝒗 In 1905 Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets (Photon). Nobel Prize 1921.

• The energy of the light must exceed certain value for emission of electrons to occur.

• The intensity of the light doesn’t affect the energy of the electrons, but it affects the number of emitted electrons


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http://en.wikipedia.org/wiki/1905_in_science

http://en.wikipedia.org/wiki/Albert_Einstein

ℎ𝑣 = 𝐵𝐸 + 𝐾𝐸

KE

Structure on an atom

• A photon (E=ℎ𝑣) is absorbed by an electron

• The electron is emitted from the atom with certain KE


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Periodicity Table, binding Energies


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• Background • Principles

• Karl Manne Georg Siegbahn. Nobel Prize in Physics in 1924 "for his discoveries and research in the field of X-ray spectroscopy.”

• Kai Manne Börje Siegbahn. Nobel Prize in Physics in 1981 “for developing the method of Electron Spectroscopy for Chemical Analysis (ESCA), now usually described as X-ray photoelectron spectroscopy (XPS)”


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http://en.wikipedia.org/wiki/Nobel_Prize_in_Physics

http://en.wikipedia.org/wiki/X-ray_spectroscopy



http://en.wikipedia.org/wiki/Nobel_Prize_in_Physics

http://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy





KE

Photon (X-ray) Source

Electron Energy

Detector


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Vacuum Level

Work Function Φ

Valence Band

1s

2s

2p

3s

3p

3d

K

L1

L2,3

M, etc

Emitted Photoelectron

Kinetic Energy (KE) X-ray

hv

X-ray Photoelectron Spectroscopy (XPS)

Courtesy of O. Furlong (UNSL) Columbia University, Oct 14th 2015. Anibal

Boscoboinik - CFN, Brookhaven Lab 14



KE Lab X-ray source

Synchrotron

Electron Analyzer


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Why is XPS surface sensitive?


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Electron Escape Depth


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KE Lab X-ray source

Synchrotron

Electron Analyzer


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1s binding energies for these elements: B, C, O, Be, F, Li, N

1 2

3

4

5

6 7


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1s binding energies for these elements: B, C, O, Be, F, Li, N

1 2

3

4

5

6 7


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Aluminum Plate

O 1s

C 1s

Al 2s Al 2p

O 2s

O Auger

William Durrer, Ph.D. Department of Physics at the Univertsity of Texas at El Paso

N(E)

Binding Energy (eV)

XPS Survey EV/Step: 1 eV, Time/Step: 50 mSec, Sweeps: 10 Source: Mg K, Pass Energy: 100 eV


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Metallic Aluminum


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Metallic Aluminum What happens if we oxidize it?


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4.3 eV 2.1 eV

Oxidation State


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How can you determine the oxide thickness?


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Al - F

Al - O


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Al - F

Al - O

Chemical Shift


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XPS tells you

• What elements you have

• How much you have of each of them

• Their oxidation state

• Their coordination to other elements

• How deep they are from the surface


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Some fact about XPS

• Surface sensitive

• Traditionally carried out in UHV

• Many relevant systems require higher pressures.

–Catalysis

– Environmental and Atmospheric Chemistry

Ambient Pressure XPS

Elevated Pressures

• Developing tools at BNL

1. Ambient Pressure Photoelectron Spectroscopy (AP-PES)

• AP-XPS & AP-NEXAFS

2. Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRAS)

3. Reactor-Scanning Tunneling Microscopy (r-STM)


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Pressures up to 5 Torr. Capillary tube into Mass Spec.

AP-XPS End Station

Starr, Tenney, Boscoboinik

AP-XPS

D. E. Starr, Z. Liu, M. Hävecker, A. Knop-Gericke, H. Bluhm. Chem. Soc. Rev., 2013,42, 5833-5857

> > > >

UHV

AP

• Differential Pumping • Refocussing Lenses

d z > d

Importance of a tightly focused beam

Cone

Sample

The smaller z, the higher P0

What can we use this for?


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Catalyst Model System Simplified version of a commercial catalyst

– allows to disentangle different factors that can potentially affect the chemical reaction.

– used for surface science mechanistic studies

There is a vast set of surface science tools to study model systems:

– Scanning Tunneling Microscopy

– X-ray Photoelectron Spectroscopy

– Etc.

Bäumer et al. Phys. Chem. Chem. Phys. 2007, 9, 3541-58


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CO adsorption and dissociation on Ru(0001) at elevated pressures. David E. Starr , Hendrik Bluhm

Surface Science Volume 608, 2013, Pages 241–248

Example using AP-XPS


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A-top Bridge

Three-fold

Adsorption site on triangular surface


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Ru(0001)

Ru(0001)

23 L of CO at 300 K

Photoionization Cross Sections. https://vuo.elettra.eu/services/elements/WebElements.html

C:Ru 3d5/2 ratio (0.088) from the spectrum correlated to known coverage of 0.66 ML

hn = 390 eV hn = 638 eV


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300 K

UHV

10-6 Torr

CO pressure

10-4 Torr

0.02 Torr

0.5 Torr


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• Photon Energy: 250 eV to 2000 eV • Pressures up to 5 Torr. • Temperatures up to 900 C • Capillary tube into Mass Spec.

• We can dose elevated pressures of

gases or liquid vapors. • (only non-corrosive)

Sample goes here ( up to ~ 1 cm)

Aluminosilicate Protective Layer

p(O2) = 1 × 10-4 mbar.

850x103

800

750

700

650

600

550

500

450

400

350

300

250

200

150

100

50

CP

S

290 288 286 284 282 280 278 276

Binding Energy (eV)

CPS_20131122_01_002_Ru3d_nor AlSiO_670eV_after_annealing_770C 670(eV) 584.86(eV) 257.2(mA) CPS_20131122_01_031_Ru3d_nor AlSiO_670eV_pO2_1E-4_650c 670(eV) 584.86(eV) 239.9(mA) CPS_20131118_02_009_Ru3d_nor CPS_20131118_02_041_Ru3d_nor

68x103

64

60

56

52

48

44

40

36

32

28

24

20

CP

S

535.0 532.5 530.0 527.5 525.0

Binding Energy (eV)

CPS_20131122_01_004_O1s_nor AlSiO_670eV_after_annealing_770C 670(eV) 584.86(eV) 256.1(mA) CPS_20131122_01_032_O1s_nor CPS_20131118_02_043_O1s_nor wave0

300 K 923 K

Ru 3d O 1s R

u(0

00

1)

Al 0

.2Si

0.8

O2/R

u(0

00

1)

300 K 873 K

T-O-T

O-Ru

O-Ru Ru-CO

Ru0

RuOx

RuOx

Exposure to elevated pressures of O2

Ru 3d O 1s

pO2 = 1 × 10-4 Torr

Emmez et al. Surf. Sci. 2015, In press.


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Aluminosilicate Protective Layer

p(O2) = 1 × 10-4 mbar.

850x103

800

750

700

650

600

550

500

450

400

350

300

250

200

150

100

50

CP

S

290 288 286 284 282 280 278 276

Binding Energy (eV)

CPS_20131122_01_002_Ru3d_nor AlSiO_670eV_after_annealing_770C 670(eV) 584.86(eV) 257.2(mA) CPS_20131122_01_031_Ru3d_nor AlSiO_670eV_pO2_1E-4_650c 670(eV) 584.86(eV) 239.9(mA) CPS_20131118_02_009_Ru3d_nor CPS_20131118_02_041_Ru3d_nor

68x103

64

60

56

52

48

44

40

36

32

28

24

20

CP

S

535.0 532.5 530.0 527.5 525.0

Binding Energy (eV)

CPS_20131122_01_004_O1s_nor AlSiO_670eV_after_annealing_770C 670(eV) 584.86(eV) 256.1(mA) CPS_20131122_01_032_O1s_nor CPS_20131118_02_043_O1s_nor wave0

300 K 923 K

Ru 3d O 1s R

u(0

00

1)

Al 0

.2Si

0.8

O2/R

u(0

00

1)

300 K 873 K

T-O-T

O-Ru

O-Ru Ru-CO

Ru0

RuOx

RuOx

Emmez et al. Surf. Sci. 2015, In press.


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Useful Resources

Dynamic Periodic Table

• http://www.ptable.com/#Orbital

Useful XPS pages

• http://www.xpsfitting.com/

• http://srdata.nist.gov/xps/Default.aspx

• http://xpssimplified.com/

• https://vuo.elettra.eu/services/elements/WebElements.html


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http://www.ptable.com/#Orbital



http://www.xpsfitting.com/



http://srdata.nist.gov/xps/Default.aspx

http://srdata.nist.gov/xps/Default.aspx

http://xpssimplified.com/

http://xpssimplified.com/

https://vuo.elettra.eu/services/elements/WebElements.html




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X-ray Photoelectron Spectroscopy for Chemical Analysis · the field of X-ray spectroscopy.”...

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