The design of an integrated XPS/Raman spectroscopy instrument for - - PowerPoint PPT Presentation

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Tim Nunney

The design of an integrated XPS/Raman spectroscopy instrument for co-incident analysis

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XPS Surface Analysis

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• UV Photoelectron Spectroscopy

XPS + ...

• 4
• 2

2 4 6 8 10 12 14 16 18 20

Intensity

Binding Energy (eV) UPS He(I) (21.2 eV) UPS He(II) (40.8 eV) XPS (1486.6 eV)

As rec SnO

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• UV Photoelectron Spectroscopy
• Ion Scattering Spectroscopy

XPS + ...

Scattering Atom Mass = M2 Incident Ion Mass = M1 KE = E0 Detected Scattered Ion Mass = M1 KE = ES Scattering Angle

θ

Key: Known Measured Calculated

Sample surface

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• UV Photoelectron Spectroscopy
• Ion Scattering Spectroscopy
• REELS

XPS + ...

Coating

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(Some) other analysis techniques

EDS High spatial resolution imaging Rapid image analysis Raman Chemical bonding information Structural information FTIR Chemical bonding information Molecular ‘fingerprint’ XRF Elemental composition High sensitivity XRD Structural information Crystallinity and composition XPS Quantitative chemical state Very surface sensitive

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Other techniques

XPS Quantitative chemical state Very surface sensitive EDS High spatial resolution imaging Rapid image analysis Raman Chemical bonding information Structural information FTIR Chemical bonding information Molecular ‘fingerprint’ XRF Elemental composition High sensitivity XRD Structural information Crystallinity and composition

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Raman Spectroscopy

Rayleigh scattering

(filtered out)

Raman scattering

(Stokes shift)

200 400 600 800 1000 1200 1400 1600 1800 2000 Raman shift (cm-1)

Blocking Filter

Excitation frequency

V = 0

Rayleigh scattering

V = 1

Raman scattering ~~~~~~~~~~~~~~~ V = virtual state

LASER Sample Optics

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XPS-Raman

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• Integration of small form factor Thermo

Scientific™ iXR Raman spectrometer with

• Thermo Scientific™ Theta Probe and
• Thermo Scientific™ Nexsa XPS systems
• Allows simultaneous acquisition of

Raman & XPS data

• Correlated analysis position
• No need to move the sample to acquire data
• Analysis area is matched
• Software control allows complex hybrid

experiments

XPS with iXR Raman Spectrometer

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Co-alignment of analysis positions

Raman Beam X-Ray Beam

600% Zoom

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Lithium niobate

Raman intensity (counts/s)

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Lithium niobate...?

XPS intensity (counts/s) Raman intensity (counts/s)

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Bulk vs surface

• For strongly absorbing materials such as semiconductors, the Raman signal is acquired

from a volume defined by the Raman penetration depth and the diameter of the laser beam

• A lower laser wavelength gives smaller penetration and provides chemical information

closer to the samples surface

• Nominal XPS sampling depth is ≤ 10 nm

Laser Wavelength (nm) Penetration Depth in Si (nm) Penetration Depth in Ge (nm) Penetration depth in a transparent Polymer Film (nm) 633 3000 30 >5000 514 760 19 >5000 488 570 18 >5000 457 310 18 >5000 325 10 9 >5000 244 6 7 >5000

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Lithium niobate with yttrium oxide coating

XPS intensity (counts/s) Raman intensity (counts/s)

Bulk Surface

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Applications Area: Carbon

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Graphene on SiO2

Raman imaging of damaged graphene layer deposited on a silicon wafer (Mapping controlled through Avantage software)

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Graphene – PCA analysis of map

Graphene area Damaged area

2D G D Si band Si band 8 mW 50 µm pinhole 15 x 10s acquisitions No graphene signal from damage zone

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Graphene - XPS

Both areas are contaminated by the adhesive material in the container that the sample was face down on. Not visible in Raman, but easy to see in XPS.

Contamination Contamination

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TiO2 powders

Introduction

• Titanium dioxide (TiO2)
• Material of great interest due to its application

in heterogeneous catalysis, dye-sensitised solar cells, bone implants and self-cleaning windows, amongst others

• Frontier material in the development of

nanotechnology, nanoparticles, nanorods etc. fabricated to improve application properties

• Most abundant polymorphs are rutile and

anatase

• Degree of mixing between two polymorphs

influences material properties, such as catalytic activity

Anatase-TiO2 Rutile-TiO2

Oxygen Titanium

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448 450 452 454 456 458 460 462 464 466 468 470 472 474

Ti2p Scan

TiO2 powders

XPS of single polymorph

Binding Energy (eV) Counts / s

10 20

valence band

Rutile-TiO2 Anatase-TiO2

Data offset slightly for clarity

• Core level XPS spectra show

identical elemental and chemical composition for pure anatase and pure rutile samples

• There is a slight variation in

peak shape of valence band, however this is not conducive to easy quantification of the amount of polymorph.

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300 400 500 600 700 800

Raman TiO2 spectra – Linear background subtracted

TiO2 powders

Raman spectroscopy of single polymorphs

Anatase-TiO2 powder Rutile-TiO2 powder

• Raman spectra were acquired

from pure anatase-TiO2 and rutile-TiO2 powders

• Pure spectra can be used as

reference for determining the composition of powders with different proportions of anatase and rutile

Intensity (norm.) Raman Shift (cm-1)

Eg A1g B1g Eg A1g

610.6 445.8 637.7 515.3 396.7

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TiO2 powders

Raman spectroscopy of mixed powders

300 400 500 600 700 800

Sample #3

300 400 500 600 700 800

Sample #2

300 400 500 600 700 800

Sample #1

Counts / s Pure Anatase reference Pure Rutile reference Fit of combined reference spectra Mixed powder spectrum Raman Shift (cm-1)

Anatase:Rutile

9:91

Anatase:Rutile

49:51

Anatase:Rutile

71:29

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• Adding extra analytical techniques increases

the information that can be obtained.

• Matching the technique to the application is

important

• Having co-incident analysis points ensures that

the data is collected from the same point on the sample, but...

• ...consideration must be made of variations

between analysis volumes.

• Offers opportunities for
• Bulk – surface studies
• Carbon nanomaterials
• Coating analysis
• .....

Summary