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 Internship in the Chemistry Laboratory of TE-VSC-SCC 29 August, 2014 TE-VSC 1/28
Table ble of of Contents Contents • Introduction • FTIR spectroscopy at grazing incidence • Experiments on Stainless Steel – Baseline Distortions – Detection Limit • Conclusion 29 August, 2014 TE-VSC 2/28
Table ble of of Contents Contents • Introduction • FTIR spectroscopy at grazing incidence • Experiments on Stainless Steel – Baseline Distortions – Detection Limit • Conclusion 29 August, 2014 TE-VSC 3/28
Intr Introduction oduction • Current procedure for organic contamination: – Extraction with n-Hexane (304 ml/m 2 ) – Deposition of 2 drops of extraction solution on 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
Intr Introduction oduction • Transmission spectrum for an organic contaminant 1.007 CO2 1.006 Water Water 1.005 1.004 1.003 Transmittance C-H stretching 1.002 peaks 1.001 1 0.999 1 monolayer on the sample 0.998 Ref 0.997 0.1 µg/cm2 0.996 3750 3250 2750 2250 1750 1250 750 Wavenumber [cm -1 ] 29 August, 2014 TE-VSC 5/28
Intr Introduction oduction • 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
Intr Introduction oduction • The portable Agilent 4100 ExoScan FTIR Diamond Diffuse Grazing ATR Reflectance Angle 82 ◦ For the For the For the identification measurement of measurement of polymers, rough surfaces of thin films powders ( 𝑒 < 𝜇 ) 29 August, 2014 TE-VSC 7/28
Pr Previous vious Study Study • Detection of Silicones down to 0.1 µg/cm 2 – Stainless Steel – Copper – Aluminum • Detection of Hydrocarbons down to 0.1 µg/cm 2 – Copper – Aluminum – Stainless Steel Problems 29 August, 2014 TE-VSC 8/28
Table ble of of Contents Contents • Introduction • FTIR spectroscopy at grazing incidence • Experiments on Stainless Steel – Baseline Distortions – Detection Limit • Conclusion 29 August, 2014 TE-VSC 9/28
FTIR FTIR at t grazing incidence azing incidence • Vibrational Spectroscopy Requirements for excitation: δ - δ + δ - • Oscillating dipole moment µ Alignment of the electric field vector of • the radiation with the oscillating dipole 29 August, 2014 TE-VSC 10/28
FTIR FTIR at g t grazing incidence azing incidence • Polarization of light Metal Surface • P-polarized light parallel to the plane of incidence • S-polarized light perpendicular to the plane of incidence 29 August, 2014 TE-VSC 11/28
FTIR FTIR at g t grazing incidence azing incidence • Image charge A conducting surface 29 August, 2014 TE-VSC 12/28
FTIR FTIR at g t grazing incidence azing incidence • The effect of the image charge Metal Surface No net dipole oscillation The dipole oscillation No absorption is amplified 29 August, 2014 TE-VSC 13/28
FTIR at g FTIR t grazing incidence azing incidence • How to excite this vibration? I 0 E p I 0 E p 𝜄 = 82 ◦ Metal Surface But… You need an angle θ > 0 In conclusion: Good absorbance only for a large angle of incidence 𝜄 29 August, 2014 TE-VSC 14/28
Table ble of of Contents Contents • Introduction • FTIR spectroscopy at grazing incidence • Experiments on Stainless Steel – Baseline Distortions – Detection Limit • Conclusion 29 August, 2014 TE-VSC 15/28
Baseline Distor Baseline Distortions tions • Roughness Induced Baseline Distortions • Film Induced Baseline Distortions 29 August, 2014 TE-VSC 16/28
Baseline Distortions Baseline Distor tions • Roughness Induced Baseline Distortions 104 Electropolished 102 Stainless Steel Reference 100 98 Reflectance [%] 96 94 92 Rough Stainless Increasing the 90 Steel Samples roughness (clean) 88 86 3650 3150 2650 2150 1650 1150 650 Wavenumber [cm -1 ] Short wavelengths Large wavelengths Light only ‘sees’ objects larger or approximately equal to its wavelength 29 August, 2014 TE-VSC 17/28
Baseline Distor Baseline Distortions tions • Film Induced Baseline Distortions 82 ◦ Air 𝑜 1 = 1 42 ◦ Paraffin 𝑜 2 = 1.473 Stainless Steel • The angle of incidence for the metal surface changes • Higher refractive index 29 August, 2014 TE-VSC 18/28
Baseline Distor Baseline Distortions tions • Calculation of the baseline (MATLAB) – Approximations: • The complex refractive index of iron as a function of wavenumber • The refractive index of Paraffin: 𝑜 2 = 1.473 (n20/D) The calculation will yield: Only the baseline, not the carbon-hydrogen stretching peaks 29 August, 2014 TE-VSC 19/28
Baseline Distor Baseline Distortions tions • Calculation of the baseline (MATLAB) The higher the concentration, the bigger the baseline distortion But negligible compared to the effect of the roughness 29 August, 2014 TE-VSC 20/28
Baseline Distor Baseline Distortions tions • Calculation of the baseline (MATLAB) 103.5 103 102.5 Reflectance [%] 102 MATLAB 101.5 Exp. 1 µg/cm2 101 100.5 100 99.5 99 3650 3150 2650 2150 1650 1150 650 Wavenumber [cm -1 ] Comparison with a Paraffin film on a electropolished Stainless Steel surface (experiment) 29 August, 2014 TE-VSC 21/28
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
Detection Limi Detection Limit • Electropolished Stainless Steel Surface 1.002 1 0.998 Ref Stainless Steel is 0.1 µg/cm2 0.996 Reflectance not the cause of the 0.2 µg/cm2 problems! 0.994 0.3 µg/cm2 0.4 µg/cm2 0.992 0.5 µg/cm2 0.99 1 µg/cm2 0.988 80 0.986 70 3100 3050 3000 2950 2900 2850 2800 2750 2700 60 Wavenumber [cm -1 ] Area under the peaks 50 40 30 y = 142.79x - 10.199 20 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Surface concentration [ µ g/cm2] 29 August, 2014 TE-VSC 23/28
Rough Surf ough Surfaces aces Electropolished Rough Surface Sandblasted 29 August, 2014 TE-VSC 24/28
Rough Surf ough Surfaces aces 104 Electropolished 102 Stainless Steel Reference 100 98 Reflectance [%] 96 94 92 Rough Stainless Increasing the 90 Steel Samples roughness (clean) 88 86 3650 3150 2650 2150 1650 1150 650 Wavenumber [cm -1 ] 29 August, 2014 TE-VSC 25/28
Rough Surf ough Surfaces aces 110 108 106 Rough Stainless Reflectance [%] Steel Samples Ref 104 0.2 µg/cm2 0.2 µg/cm2 102 0.2 µg/cm2 Rough Stainless Steel Reference 100 98 96 3650 3150 2650 2150 1650 1150 650 Wavenumber [cm -1 ] The samples are rougher than the reference 29 August, 2014 TE-VSC 26/28
Rough Surf ough Surfaces aces • Rough Stainless Steel Sample & Rough Stainless Steel Reference 107.5 107 Reflectance [%] 0.2 µg/cm2 106.5 0.2 µg/cm2 0.2 µg/cm2 106 105.5 3100 3050 3000 2950 2900 2850 2800 2750 2700 Wavenumber [cm -1 ] The more signal is lost, the smaller the peaks become. 29 August, 2014 TE-VSC 27/28
Conc Conclusion lusion • Detection of Hydrocarbons on smooth Stainless Steel surfaces is possible down to 0.1 µg/cm 2 (= 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
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 29 August, 2014 TE-VSC 29
FTIR FTIR Spectr Spectroscop oscopy • Why Fourier Transform? 29 August, 2014 TE-VSC 30
Oxidiz Oxidized ed Stainless Stainless Steel Steel • Electropolished stainless steel plates • 300 ° C for 2.5 days 1.001 1 0.999 0.998 0.997 Reflectance Ref 0.1 µg/cm2 0.996 0.3 µg/cm2 0.995 0.5 µg/cm2 0.994 1 µg/cm2 0.993 0.992 0.991 3100 3050 3000 2950 2900 2850 2800 2750 2700 Wavenumber [cm -1 ] 29 August, 2014 TE-VSC 31
The Calcula he Calculation tion • The Fresnel equations 𝒔 𝒒 = 𝒐 𝟑 ∙ 𝒅𝒑𝒕 𝜾 𝟐 − 𝒐 𝟐 ∙ 𝒅𝒑𝒕 𝜾 𝟑 𝒐 𝟑 ∙ 𝒅𝒑𝒕 𝜾 𝟐 + 𝒐 𝟐 ∙ 𝒅𝒑𝒕 𝜾 𝟑 𝒔 𝒕 = 𝒐 𝟐 ∙ 𝒅𝒑𝒕 𝜾 𝟐 − 𝒐 𝟑 ∙ 𝒅𝒑𝒕 𝜾 𝟑 𝒐 𝟐 ∙ 𝒅𝒑𝒕 𝜾 𝟐 + 𝒐 𝟑 ∙ 𝒅𝒑𝒕 𝜾 𝟑 • Snell’s law 𝒐 𝟐 ∙ 𝒕𝒋𝒐 𝜾 𝟐 = 𝒐 𝟑 ∙ 𝒕𝒋𝒐 𝜾 𝟑 29 August, 2014 TE-VSC 32
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