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FTIR FTIR spectr spectroscop oscopy a y at t grazing incidence f azing incidence for or surf surface c ace chemica hemical l anal analys ysis is Gertjan Lippertz Student Nanoscience & Nanotechnology, KU Leuven, Belgium

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SLIDE 1

FTIR FTIR spectr spectroscop

  • scopy a

y at t grazing incidence f azing incidence for

  • r

surf surface c ace chemica hemical l anal analys ysis is

Gertjan Lippertz

29 August, 2014 TE-VSC 1/28

Student Nanoscience & Nanotechnology, KU Leuven, Belgium Internship in the Chemistry Laboratory of TE-VSC-SCC

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SLIDE 2

Table ble of

  • f Contents

Contents

  • Introduction
  • FTIR spectroscopy at grazing incidence
  • Experiments on Stainless Steel

– Baseline Distortions – Detection Limit

  • Conclusion

29 August, 2014 TE-VSC 2/28

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SLIDE 3

Table ble of

  • f Contents

Contents

  • Introduction
  • FTIR spectroscopy at grazing incidence
  • Experiments on Stainless Steel

– Baseline Distortions – Detection Limit

  • Conclusion

29 August, 2014 TE-VSC 3/28

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SLIDE 4

Intr Introduction

  • duction
  • Current procedure for organic contamination:

– Extraction with n-Hexane (304 ml/m2) – Deposition of 2 drops of extraction solution

  • n a ZnS cell

– The n-Hexane evaporates from the cell – The organic contamination remains on the surface of the cell and is analysed with FTIR (in transmission)

29 August, 2014 TE-VSC 4/28

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SLIDE 5

Intr Introduction

  • duction
  • Transmission spectrum for an organic

contaminant

29 August, 2014 TE-VSC 5/28 0.996 0.997 0.998 0.999 1 1.001 1.002 1.003 1.004 1.005 1.006 1.007 750 1250 1750 2250 2750 3250 3750 Transmittance Wavenumber [cm-1] Ref 0.1 µg/cm2

Water Water CO2 C-H stretching peaks

 1 monolayer on the sample

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SLIDE 6

Intr Introduction

  • duction
  • Disadvantages:

– n-Hexane is toxic – The sample has to be dismounted and transported to the chemistry laboratory – Complex geometries can cause problems – Only the average surface contamination – Solubility in n-Hexane

29 August, 2014 TE-VSC 6/28

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SLIDE 7

Intr Introduction

  • duction
  • The portable Agilent 4100 ExoScan FTIR

29 August, 2014 TE-VSC 7/28

Diffuse Reflectance Diamond ATR Grazing Angle 82◦ For the identification

  • f polymers,

powders For the measurement of rough surfaces For the measurement

  • f thin films

(𝑒 < 𝜇)

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SLIDE 8

Pr Previous vious Study Study

  • Detection of Silicones down to 0.1 µg/cm2

– Stainless Steel – Copper – Aluminum

  • Detection of Hydrocarbons down to 0.1 µg/cm2

– Copper – Aluminum – Stainless Steel  Problems

29 August, 2014 TE-VSC 8/28

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SLIDE 9

Table ble of

  • f Contents

Contents

  • Introduction
  • FTIR spectroscopy at grazing incidence
  • Experiments on Stainless Steel

– Baseline Distortions – Detection Limit

  • Conclusion

29 August, 2014 TE-VSC 9/28

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SLIDE 10

FTIR FTIR at t grazing incidence azing incidence

  • Vibrational Spectroscopy

29 August, 2014 TE-VSC 10/28

Requirements for excitation:

  • Oscillating dipole moment µ
  • Alignment of the electric field vector of

the radiation with the oscillating dipole δ- δ- δ+

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SLIDE 11

FTIR FTIR at g t grazing incidence azing incidence

  • Polarization of light

29 August, 2014 TE-VSC 11/28

Metal Surface

  • P-polarized light  parallel to the plane of incidence
  • S-polarized light  perpendicular to the plane of incidence
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SLIDE 12

FTIR FTIR at g t grazing incidence azing incidence

  • Image charge

29 August, 2014 TE-VSC 12/28

A conducting surface

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SLIDE 13

FTIR FTIR at g t grazing incidence azing incidence

  • The effect of the image charge

29 August, 2014 TE-VSC 13/28

Metal Surface

No net dipole oscillation No absorption The dipole oscillation is amplified

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SLIDE 14

FTIR FTIR at g t grazing incidence azing incidence

  • How to excite this vibration?

29 August, 2014 TE-VSC 14/28

Metal Surface But… You need an angle θ > 0 Ep I0 In conclusion: Good absorbance only for a large angle of incidence 𝜄 Ep I0

𝜄 = 82◦

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SLIDE 15

Table ble of

  • f Contents

Contents

  • Introduction
  • FTIR spectroscopy at grazing incidence
  • Experiments on Stainless Steel

– Baseline Distortions – Detection Limit

  • Conclusion

29 August, 2014 TE-VSC 15/28

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SLIDE 16

Baseline Distor Baseline Distortions tions

  • Roughness Induced Baseline Distortions
  • Film Induced Baseline Distortions

29 August, 2014 TE-VSC 16/28

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SLIDE 17

Baseline Distor Baseline Distortions tions

  • Roughness Induced Baseline Distortions

29 August, 2014 TE-VSC 17/28 86 88 90 92 94 96 98 100 102 104 650 1150 1650 2150 2650 3150 3650 Reflectance [%] Wavenumber [cm-1]

Electropolished Stainless Steel Reference Rough Stainless Steel Samples (clean) Increasing the roughness Light only ‘sees’ objects larger or approximately equal to its wavelength

Large wavelengths Short wavelengths

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SLIDE 18

Baseline Distor Baseline Distortions tions

  • Film Induced Baseline Distortions

29 August, 2014 TE-VSC 18/28

  • The angle of incidence for the metal surface changes
  • Higher refractive index

Paraffin 𝑜2 = 1.473 Stainless Steel 82◦ 42◦ Air 𝑜1 = 1

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SLIDE 19

Baseline Distor Baseline Distortions tions

  • Calculation of the baseline (MATLAB)

– Approximations:

  • The complex refractive index of iron as a function
  • f wavenumber
  • The refractive index of Paraffin:

𝑜2 = 1.473 (n20/D)

29 August, 2014 TE-VSC 19/28

The calculation will yield: Only the baseline, not the carbon-hydrogen stretching peaks

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SLIDE 20

Baseline Distor Baseline Distortions tions

  • Calculation of the baseline (MATLAB)

29 August, 2014 TE-VSC 20/28

The higher the concentration, the bigger the baseline distortion But negligible compared to the effect of the roughness

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SLIDE 21

Baseline Distor Baseline Distortions tions

  • Calculation of the baseline (MATLAB)

29 August, 2014 TE-VSC 21/28 99 99.5 100 100.5 101 101.5 102 102.5 103 103.5 650 1150 1650 2150 2650 3150 3650 Reflectance [%] Wavenumber [cm-1] MATLAB

  • Exp. 1 µg/cm2

Comparison with a Paraffin film on a electropolished Stainless Steel surface (experiment)

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SLIDE 22

The Contamina he Contamination tion

  • The contamination standard for hydrocarbons:

– Cutting oil: Blasocut BC 35 LF SW (33 vol%) – Machine oil: Shell Vitrea 150 (33 vol%) – Bearing grease: Kluber Isoflex NBU 15 (33 vol%)

  • Dissolve in n-Hexane (for spectroscopy)
  • Switch to Paraffin (for spectroscopy)

29 August, 2014 TE-VSC 22/28

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SLIDE 23

Detection Limi Detection Limit

  • Electropolished Stainless Steel Surface

29 August, 2014 TE-VSC 23/28 0.986 0.988 0.99 0.992 0.994 0.996 0.998 1 1.002 2700 2750 2800 2850 2900 2950 3000 3050 3100 Reflectance Wavenumber [cm-1] Ref 0.1 µg/cm2 0.2 µg/cm2 0.3 µg/cm2 0.4 µg/cm2 0.5 µg/cm2 1 µg/cm2 y = 142.79x - 10.199 10 20 30 40 50 60 70 80 0.1 0.2 0.3 0.4 0.5 0.6 Area under the peaks Surface concentration [µg/cm2]

Stainless Steel is not the cause of the problems!

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SLIDE 24

Rough Surf

  • ugh Surfaces

aces

29 August, 2014 TE-VSC 24/28

Electropolished Rough Surface Sandblasted

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SLIDE 25

Rough Surf

  • ugh Surfaces

aces

29 August, 2014 TE-VSC 25/28 86 88 90 92 94 96 98 100 102 104 650 1150 1650 2150 2650 3150 3650 Reflectance [%] Wavenumber [cm-1]

Electropolished Stainless Steel Reference Rough Stainless Steel Samples (clean) Increasing the roughness

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SLIDE 26

Rough Surf

  • ugh Surfaces

aces

29 August, 2014 TE-VSC 26/28 96 98 100 102 104 106 108 110 650 1150 1650 2150 2650 3150 3650 Reflectance [%] Wavenumber [cm-1] Ref 0.2 µg/cm2 0.2 µg/cm2 0.2 µg/cm2

Rough Stainless Steel Reference Rough Stainless Steel Samples

The samples are rougher than the reference

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SLIDE 27

Rough Surf

  • ugh Surfaces

aces

  • Rough Stainless Steel Sample & Rough Stainless Steel

Reference

29 August, 2014 TE-VSC 27/28 105.5 106 106.5 107 107.5 2700 2750 2800 2850 2900 2950 3000 3050 3100 Reflectance [%] Wavenumber [cm-1] 0.2 µg/cm2 0.2 µg/cm2 0.2 µg/cm2

The more signal is lost, the smaller the peaks become.

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SLIDE 28

Conc Conclusion lusion

  • Detection of Hydrocarbons on smooth

Stainless Steel surfaces is possible down to 0.1 µg/cm2 (= 1 monolayer)

  • Detection on rough surfaces is an issue for

– Stainless Steel But possibly also for – Copper – Aluminum

29 August, 2014 TE-VSC 28/28

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SLIDE 29

29 August, 2014 TE-VSC 29

Questions ? Questions ?

Acknowledgements: Paolo Chiggiato & Mauro Taborelli The Chemistry Laboratory: Benoit Teissandier, Colette Charvet, Laetitia Bardo & Radu Setnescu The Surface Treatment Workshop: Florent Fesquet, Pierre Maurin & Jacky Carosone The Polymer Laboratory

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SLIDE 30

FTIR FTIR Spectr Spectroscop

  • scopy
  • Why Fourier Transform?

29 August, 2014 TE-VSC 30

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SLIDE 31

Oxidiz Oxidized ed Stainless Stainless Steel Steel

  • Electropolished stainless steel plates
  • 300°C for 2.5 days

29 August, 2014 TE-VSC 31 0.991 0.992 0.993 0.994 0.995 0.996 0.997 0.998 0.999 1 1.001 2700 2750 2800 2850 2900 2950 3000 3050 3100 Reflectance Wavenumber [cm-1] Ref 0.1 µg/cm2 0.3 µg/cm2 0.5 µg/cm2 1 µg/cm2

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SLIDE 32

The Calcula he Calculation tion

  • The Fresnel equations
  • Snell’s law

29 August, 2014 TE-VSC 32

𝒔𝒒 = 𝒐𝟑 ∙ 𝒅𝒑𝒕 𝜾𝟐 − 𝒐𝟐 ∙ 𝒅𝒑𝒕 𝜾𝟑 𝒐𝟑 ∙ 𝒅𝒑𝒕 𝜾𝟐 + 𝒐𝟐 ∙ 𝒅𝒑𝒕 𝜾𝟑 𝒔𝒕 = 𝒐𝟐 ∙ 𝒅𝒑𝒕 𝜾𝟐 − 𝒐𝟑 ∙ 𝒅𝒑𝒕 𝜾𝟑 𝒐𝟐 ∙ 𝒅𝒑𝒕 𝜾𝟐 + 𝒐𝟑 ∙ 𝒅𝒑𝒕 𝜾𝟑 𝒐𝟐 ∙ 𝒕𝒋𝒐 𝜾𝟐 = 𝒐𝟑 ∙ 𝒕𝒋𝒐 𝜾𝟑

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SLIDE 33

The Calcula he Calculation tion

  • The reflectance of a thin film on a metal

surface (= stratified medium)

29 August, 2014 TE-VSC 33

𝒔𝒌 = 𝒔𝟐𝟑,𝒌 + 𝒔𝟑𝟒,𝒌 ∙ 𝒇𝟑∙𝒋∙𝜸 𝟐 + 𝒔𝟐𝟑,𝒌 ∙ 𝒔𝟑𝟒,𝒌 ∙ 𝒇𝟑∙𝒋∙𝜸 𝒙𝒋𝒖𝒊 𝒌 = 𝒒 𝒑𝒔 𝒕 𝜸 =

𝟑𝝆 𝝁𝟏 ∙ 𝒐𝟑 ∙ 𝒎 ∙ 𝒅𝒑𝒕 𝜾𝟑

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SLIDE 34

The Calcula he Calculation tion

29 August, 2014 TE-VSC 34

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SLIDE 35

The Calcula he Calculation tion

  • The reflectance

29 August, 2014 TE-VSC 35

𝑺𝒌 = 𝒔𝒌

𝟑

𝑺𝒗 = 𝑺𝒒 + 𝑺𝒕 𝟑 𝑻𝒒𝒇𝒅𝒖𝒔𝒗𝒏 = 𝑺𝒒,𝒈𝒋𝒎𝒏 + 𝑺𝒕,𝒈𝒋𝒎𝒏 𝑺𝒒,𝒐𝒑 𝒈𝒋𝒎𝒏 + 𝑺𝒕,𝒐𝒑 𝒈𝒋𝒎𝒏

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SLIDE 36

The Calcula he Calculation tion

29 August, 2014 TE-VSC 36

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SLIDE 37

Vibr ibrational tional Spectr Spectroscop

  • scopy

29 August, 2014 TE-VSC 37

𝑾𝒋𝝃 = 𝒊𝝃𝒋 𝒘𝒋 + 𝟐 𝟑 + 𝒊𝝃𝒋𝒚𝒋 𝒘𝒋 + 𝟐 𝟑

𝟑

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SLIDE 38

Raw Spectr Raw Spectra

  • Bruker Vertex 70

29 August, 2014 TE-VSC 38 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 650 1150 1650 2150 2650 3150 3650

Wavenumber [cm-1]

Ref Sample