Characterization of Ti-based surfaces with X-ray

Characterization of Ti-based surfaces with X-ray photoelectron spectroscopy Janez Kovač Jožef Stefan Institute Ljubljana, Slovenia E-mail: [email protected]

Outlook • X-Ray photoelectron spectroscopy – – – – – –

Principles Surface sensitivity Quantification Chemical shift Instrumentation Depth profiling

• Applications of XPS and AES – Ti valence states on Ti-O ceramics – TiO2 anatase layer/Ti6Al4V alloy – Rejected Ti implant from a patient

X-Ray Photoelectron SpectroscopyXPS • Irradiation of solid surface with monohromatic X-ray photons (E~1000 eV, λ∼1 nm) and energy analysis of emitted photoelectrons • High surface sensitivity X-rays • Information on: – Composition – Chemical state of elements

emitted electrons

XPS – Photoelectron process Emitted electron, EK EVAKUUM EFermi Valelence band

2s

X-ray photon, hν

1s

Energy levels in carbon

Binding energy (eV)

2p

XPS spectrum XPS survey spectrum of InP

Intensity (a.u.)

InP(100)

•Spin-orbit splitting: 2p3/2,2p1/2

In 3d

Concentrations: In...31.6 at.% C...29.0 at.% O...27.0 at.% P...12.4 at.%

•Valence band Surface contamination

O 1s

•Auger peaks

In 3p

O KLL

1200

•XPS peaks: 1s, 2s, 2p...

1000

In 3s C 1s

800

600

400

Binding Energy (eV)

Binding Energy (eV) Kinetic Energy (eV)

•Background due to inelasic scattering

In 4d P 2s P 2p

200

0

Surface sensitivity Inelastic mean free path – IMFP: λ ~ 0.3 - 4 nm 95% of the measured peak intensity comes from a sampling depth of 3λicosθ (θ=angle of emission)

Quantification I = j ⋅ c ⋅σ ⋅ K ⋅ λ j - x-ray flux c - concentration of element

σ - cross-section for photoelectron excitation K - instrumental factors

λ - electron inelastic mean free path

Ii ci =

∑ j

Si

Ij

Si: Relative sensitivity factor Ci: concentration in at.%

Sj

• Sensitivity of XPS ~ 0.1 at.% • Possible to detect all elements except H and He

Chemical shift in XPS Electrons at inner orbitales (core levels) feel different potential due to different chemical bonds of atom by valence electrons ⇒ change in binding energy = chemical shift (up to few eV) ⇒ Model: ΔE= k Δq + ΔV (charge potential model) ⇒ information about: 1. Valence states 2. Chemical environment

Chemical shift in XPS: a tool to recognize chemical compounds Intensity (a.u.)

Ti 2p

Ti 2p3/2

TiO2

Ti (4+) Ti 2p1/2

475

470

465

460

455

450

Binding Energy (eV)

Ti 2p3/2

Intensity (a.u.)

Ti 2p Ti-suboxides

Ti (4+)

Ti 2p1/2

Ti (3+) Ti (2+)

475

470

465

460

Binding Energy (eV)

455

450

UHV ambient • Why a need for UHV? – 10-8 to 10-10 mbar

• Surface contamination at 10-6 mbar, a monolayer of gas is adsorbed onto solid surface in about one second

• Scattering of photoelectrons

XPS spectrometer Complex, ultra high vacuum instrument: • • • • • •

X-ray sources, electron energy analyser, ion gun, neutralizer, sample manipulator p ~ 10-10 mbar

X-ray sources for XPS • X-ray tubes (laboratory): – Mg anode, – Al anode,

E=1253.6 eV, FWHM=0.70 eV E=1486.6 eV, FWHM=0.85 eV

Quartz monochromator (FWHM ~ 0.25 eV)

• Synchrotron radiation tunable energy, high flux, high monochromaticy, very small spot X-ray beam (<100 nm) (Synchrotron Elettra at Trieste (IT)

Applications Studies of phenomena at surfaces and interfaces: • oxidation, • adhesion, • adsorption, • contamination, • segregation, • diffusion, • surface functionalization • reactions at internal interfaces • thin films • …

Effect of the valence state of titanium ions on hydrophilicity of ceramics in Ti-O system •

TiO2 : photocatalytic and superhydrophilic effects

•

To study effect of valence states of Ti-atoms on WCA

•

TiO2 ceramic was prepared from TiO2 powder sintered in air, reduced TiO2-x ceramic from TiO2-x powder sintered in Ar/H2 Ti2O3 ceramic from mechanochemically activated Ti2O3 powder sintered in Ar/H2.

• •

•

All powders were sintered at 1400 oC for 2 hours

SEM image of TiO2−x powder and (b) X-ray powder-diffraction pattern of TiO2−x powder.

D. Kuščer et al., Journal of the European Ceramic Society 28 (2008) 577–584

Effect of the valence state of titanium ions on hydrophilicity of ceramics in Ti-O system O 1s

Intensities (a.u.)

Ti 2p O KLL

C 1s

Ti LMM

Ti 3p

Ti2O3 Ba 3d Ca 2p

TiO2-x

Mg KLL

TiO2 1000

800

600

400

Si 2p

200

Binding Energy (eV) D. Kuščer et al., Journal of the European Ceramic Society 28 (2008) 577–584

0

Effect of the valence state of titanium ions on hydrophilicity of ceramics in Ti-O system Ti4+

Normalized Intensities (a.u.)

Ti 2p

Ti3+ Ti3+/Ti total

Ti2O3

9%

TiO2-x 14 %

TiO2 475

470

0% 465

460

455

Binding Energy (eV) D. Kuščer et al., Journal of the European Ceramic Society 28 (2008) 577–584

Effect of the valence state of titanium ions on hydrophilicity of ceramics in Ti-O system Ti 2p spekter, vz. 2, TiO2-x

TiO2-x

2500

Ti 2p

4+

Signal (impulzi/s)

2000

1500

4+ 3+

3+

1000

500

80 Water contact angle (degree)

3000

67

70 60 50 40 26

30 20

18

10

0

0 470

468

466

464

462 460 Vezavna energija (eV)

458

456

454

Ti2O3

TiO2-x

TiO2

- The presence of Ti(3+) at surface is related to a significant decrease in water-contact angle. - Wettability of ceramics in the TiO system can be improved by introducing Ti(3+) at the ceramic interface. D. Kuščer et al., Journal of the European Ceramic Society 28 (2008) 577–584

Surface Ù subsurface • Very often information from subsurface region needed. • Depth profiling: – Angle resolved XPS: depth up to 10 nm – Ion sputtering: depth up to 500 nm

Ion sputter depth profiling EL. OR X-RAY BEAM

ION BEAM

OVERLAYER

SUBSTRAT

Schematic representation of the beginning of the AES/XPS depth profiling analysis.

XPS depth profiling with high depth resolution Ni Cr O

Cr-oxide

Ni Cr Si

depth Cr

XPS depth profile of Ni(30 nm)/Cr(30 nm)/Cr2O3(30 nm)/ Ni(30 nm)/Cr(30 nm)/Si structure

Cr-oxide Cr-metal Cr-metal

Ion sputter depth profiling • Techniques: – XPS or Auger electron spectroscopy – AES

• Information: – Depth distribution of elements in layer of thickness of about 100 500 nm

• Requirements for – Good depth resolution, sample rotation (invented by prof. Zalar in 1985 in our laboratoy)

• Drawback: destructive method, reduction of Ti valence states • Alternative techniques – TEM, RBS, FE-SEM, GDOES, SIMS

Hydrothermal synthesis of anatase layer on Ti6Al4V implants - V has been reported to be cytotoxic - Al has been suggested to be neurotoxic TiO2 layer present at the surface: • it has some bioactive properties • to prevent diffusion of toxic metal ions into the body

Non treated

After 24h at pH=8, 150 oC, with TiO2 addition

N. Drnovšek et al., Surface & Coatings Technology 203 (2009) 1462–1468

Hydrothermal synthesis of anatase layer on Ti6Al4V implants Sample preparation: at different pH values with or without the addition of TiO2 (anatase powder) or Ti(OH)4 in water suspension or NaOH or NH4NO3 solution Result: different morphologies of anatase crystals and different thickness of the oxide layer

SEM images of HT treated Ti6Al4V specimens with TiO2 addition. (a) pH=8 (natural). The surfaces of the substrate are covered with a thick layer of large anatase crystals. (b) pH=11. The size of anatase crystals is reduced.

XPS spectrum of Ti 2p obtained on the surface of the sample treated by HT in the NaOH soultion Ti 2p3/2

Ti 2p Intensity (a.u.)

E=458.8 eV (TiO2) Ti 2p1/2

475

470

465

460

455

450

Binding Energy (eV)

N. Drnovšek et al., Surface & Coatings Technology 203 (2009) 1462–1468

XPS spectra obtained on the surface and at depth of 750 nm of the sample treated by HT in the NaOH soultion

Intensity (a.u.)

V 2p

At depth ~ 750 nm

Ti 2s Ti 2p Ti 3s Al 2p O 1s

Ti 3p

Ar 2p

Surface C 1s N 1s

800

700

600

500

400

300

200

Binding Energy (eV) Difference in presence of metals: V and Al not detected at surface N. Drnovšek et al., Surface & Coatings Technology 203 (2009) 1462–1468

100

0

Depth profiles of TiO2/Ti6Al4V HT-treated in Ti(OH)4 suspention

Non-treated

100

100

90

90

Ti

70 C (at.%) O (at.%) Al (at.%) Ti (at.%) V (at.%)

60 50 40 30

O

20

C

Al

70

50

30

10

0

0 10

O

40

20

V

20

30

40

C V 0

10

20

30

Sputtering Time (min)

HT-treated in TiO2 suspention

100

90

90

80

80

70

O

60

C (at.%) O (at.%) Al (at.%) Ti (at.%) V (at.%)

C

50

Ti

40

40

50

60

70

30 20 10

Ti

70

O C1s O1s Al2p Ti2p V2p

60 50 40 30

0 20

30

40

50

60

70


V

10

V 10

90

HT-treated in NH4NO3 solution

20

0

80


Concentration (at.%)


100

C (at.%) O (at.%) Al (at.%) Ti (at.%) V (at.%)

60

10

0

Ti

80



80

C

Al

0 80

90

0

10

20

30

40

50

60

70

80


- Thick layer of TiO2 after treatment of Ti6Al4V in TiO2 suspension - No Al found in TiO2 layer - Low amount of V incorporated in the anatase structure

90

100

OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW 40

P

Orthopaedic screw removed from patient due to irritation

C

Ca

N

Ti

O

Fe

Mg

Al

Si

35

C 30

O Concentration (at.%)

Screw was for one year in metacarpal bone

Ti

25

N

20

Ti

15

Si 10

Al 5

Mg

Ca

0

Fe 0 P

50

100

150

200 250 Depth (nm)

300

350

400

Surface of screw was nitrided (TiN) Titanium screw – rejected implant

Formation of hydroxyapetite (Ca, P, O) Si and Al (to reduce friction)

Grega Klančnik et al., Materiali in tehnologije / Materials and technology 44 (2010) 5, 261–264

OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW Orthopaedic screw removed from patient due to irritation

P

C

Ca

N

Ti

O

Fe

Mg

4


Screw was for one year in metacarpal bone

5

3

Ca 2

P Mg

1

Fe 0 0

Titanium screw – rejected implant

50

100

150

200 250 Depth (nm)

300


350

400

OSSEOINTEGRATION AND REJECTION OF A TITANIUM SCREW Orthopaedic screw removed from patient due to irritation Screw was for one year in metacarpal bone

• Surface contamination: – Fe (iron containing steel tool) – Si and Al (to reduce friction)

• Accumulation of Fe and Al can cause inflammation, irritation and rejection of Tiscrew

Titanium screw – rejected implant


Conclusions • XPS is suitable technique for characterization of surface chemistry on model and realistic samples yielding information on surface composition and chemical state of elements. • In combiantion with ion sputtering XPS and AES techniques can provide information of distribution of elements in subsurface region

Characterization of Ti-based surfaces with X-ray photoelectron spectroscopy Janez Kovač Jožef Stefan Institute Ljubljana, Slovenia E-mail: [email protected]

Characterization of Ti-based surfaces with X-ray

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