1. The world leader in serving science Reflection Techniques

2. 2  Specular Reflection  Reflection Absorption  Diffuse Reflection (DRIFTS)  ATR

3. 3 Reflection Theory Optically dense medium Refractive Index > 1 90 o 100% Transmittance Refractive Index of Air = 1 No Refraction due to 0 o degree angle of incidence Angle of Incidence Reflection and Transmittance

4. 4 Refractive Index (n)  Is a measurement of optical density with respect to a vacuum (0.0).  Air has a refractive index of 1.0.  Most organic matter has a refractive index between 1.3-1.7.  Materials that have a refractive index greater then 1.0 will reflect light

5. 5 Specular Reflectance  Can be a surface or bulk analysis  Low energy experiment (2-15% of Transmission)  Little or no sample preparation  Quality of data dependent on sample properties Smart SpeculATR

6. 6 True Specular Reflectance True specular reflectance Illustration of a true specular reflectance spectrum Reflection Sample

7. 7 Kramer-Kronig Correction... Uncorrected Restrahlen Bands Kramers-Kronig Correction (Qualitative Analysis)

8. 8 Reflection-Absorption Illustration of a Reflection-Absorption spectrum Double pass transmission

9. 9 Angle of Incidence  Determines the Net Pathlength  Also determines the depth of penetration into the sample Absorption Reflection

10. 10 Mixed Result True specular component Reflection-Absorption component Dependent on Sample Surface and Sample Thickness Mixed Result

11. 11 Grazing Angle - Reflection-Absorption  Non-destructive technique for infrared sampling Ultra-Thin coatings Films Contaminants  Requires reflective (metal) substrates  Useful for molecular orientation studies

12. 12 Grazing Incidence Reflecting Substrate I Thin Film

13. 13 Nexus SAGA - Smart Aperture Grazing Angle  Allows analysis of thin films on metals  80º angle of incidence  Submicron film analysis  Built-in polarizer

14. 14 SAGA Optical Ray Trace Sample mask Polarizer Integrated apertures

15. 15 Quantitative Analysis  Use raw data - DO NOT correct using Kramer-Kronig  Dependent on sample and sample surface (smooth and homogeneous better)  Sample Thickness can be calculated this way (Hard Disk lubricant)

16. 16 Summary  Minimal Sample Preparation  Non-Destructive Technique  Requires flat samples  Sample Flexibility  Quantifiable  Easy and Fast

17. 17 Diffuse Reflectance  Analyzes scattered energy  Typically uses a support matrix  Great for powders  Collection of both reflectance and transmittance data Foundation Diffuse

18. 18 Diffuse Reflectance Specular Reflectance- Front surface reflection off analyte Diffuse Reflectance- light passes through sample particles

19. 19 Factors Affecting Diffuse Reflection Data  Refractive Index of the Sample  Particle size  Sample Homogeneity  Concentration  Sample preparation

20. 20 Diffuse Reflectance (DRIFTS CELL)... SOURCE DETECTOR MIRROR

21. 21 CPC Design  Reduces sample packing effects  Minimizes front surface reflection (specular component)  Efficient high throughput collection optics  Sample positioned below optics  No damage to optics from sample spills Input / output optics CPC Powder sample cup Compound Parabolic Concentrator

22. 22 DRIFTS Accessories Smart Collector Collector II

23. 23 Experiment is.....  Great for powders, solid surfaces, liquids, silicone carbide scraps, and ground samples  Frequency Dependent Experiment  Qualitative Correction: Kubelka-Munk  Easy - Very little Sample Preparation  Non-Destructive and Versatile  Pathlength dependent on scattering efficiency and sample characteristics

24. 24 Kubelka-Munk Conversion  Different processes occur simultaneously refraction transmission reflection diffraction scattering  Kubelka-Munk Theory D.R. = (1-R ) 2 /2R=K/S

25. 25 General Format... Absorbance Kubelka-Munk Unconverted Converted Baseline Corrected First

26. 26 Background  Sample cup filled with matrix material  Empty sample cup  Can use mirror but greater shift occurs  If using Si-carb sampler, use clean piece of Si-carb.

27. 27 Silicon Carbide Technique  One of the easiest methods for the analysis of hard to analyze rigid solids  A small adhesive backed disk of silicon carbide paper is used to abrade the surface to be analyzed  An infrared spectrum is obtained of the material adhering to the surface of the silicon carbide disk

28. 28 Quantitative Analysis  Sample preparation needs to be accurate and consistent  Weigh out sample and KBr  Keep peak intensities within linearity limits  Collecting multiple orientations and averaging the data can statistically improve the results

29. 29 Summary of Diffuse  Great technique for qualitative analysis  Very versatile and great sample flexibility  Lower throughput due to scattering effects  Kubelka-Munk conversion may aid in library searches  Can get good quantitative results

30. The world leader in serving science Attenuated Total Reflectance Theory and Practical Sample Analysis

31. 31 Attenuated Total Reflectance (ATR)  Versatile and non-destructive technique  Requires minimal sample preparation  Ideal for strong absorbers  Useful for surface characterization

32. 32 Experimental Considerations  Refractive index of ATR and sample  Pathlength requirements  Spectral range of interest  Phase of sample: solid, liquid, or gel  Chemical properties  Hardness of sample

33. 33 Light Refraction  Snell’s Law defines how light bends n i Sin q i = n r Sin q r n i = Refractive Index of the medium containing the incident light ray q i = the angle of the incident ray to the normal n r = Refractive Index of the medium containing the refracted ray of light q r = the angle of the refracted ray to the normal Attenuated Total Reflection (ATR)

34. 34 Refraction or Reflection? Ray 3, Total Internal Reflection Snell’s Law Ray trace where n i > n r 1 2 3 1 2 3 nrnr nini 1 4 Ray 2, Critical angle

35. 35 Attenuated Total Reflectance ZnSe Internal Reflection Element

36. 36 Depth of Penetration  Refractive index of ATR element  Angle of incidence of ATR element  Refractive index of sample  Wavelength  Depth of Penetration values range from 0.5 to 4.4 micrometers d p = 2   n atr   sin    n sample n atr () 2 [] 1/2

37. 37 Angle of Incidence -vs- Depth of Penetration As the Angle of Incidence Increases, the Penetration Depth Decreases

38. 38 Common crystals  KRS-5 ( 20,000-250 cm -1, RI-2.2)  Diamond (4,500-10 cm -1, RI-2.4)  ZnSe (20,000-454 cm -1, RI-2.4)  Si (8,300-660 cm -1, RI-3.4)  Ge (5,500-600 cm -1, RI-4.0)

39. 39 Depth of Penetration ZnSe (45 o ) Hexane RI = 2.4 Ge (45 o ) Hexane RI = 4.0 Si (45 o ) Hexane RI = 3.4 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance 2700 2800 2900 3000 3100 3200 Wavenumbers (cm -1 )

40. 40 D p vs. frequency Sample R.I. 1.3 1.7 Ge(4.0 RI) ZnSe(2.4 RI) 0.18 - 0.6  m*0.5 - 1.8  m* 0.21 - 0.81  m*0.8 - 3.8  m* * Numbers represent the depth of penetration for the approximate frequencies of 3500 and 800 cm -1

41. 41 Technique  Clean ATR crystal and collect background  Place sample on crystal  Use pressure device to ensure contact of solids on crystal surface  Collect spectrum  Apply ATR correction, if desired

42. 42 ATR correction Uncorrected ATR Corrected

43. 43 Single Bounce ATR Plunger Crystal Cap IR Beam Dome-shaped Ge Crystal  High refractive index works for virtually any sample  Interference free spectral range from 4000 - 675 cm -1  Dome shape Germanium crystal Focuses beam to sharp image under pressure tower Pressure tower insures optical contact for textured surface

44. 44 OMNI-Sampler

45. 45 Single bounce ATR options Smart Endurance Smart Performer

46. 46 Multi-bounce HATR Smart Multi-Bounce HATR Foundation Multi-Bounce HATR

47. 47 Multiple-Bounce -vs- Single Bounce ATR Hexane 12 reflections Hexane 10 reflections Hexane 1 reflection 0.1 0.2 0.3 0.4 Absorbance 1340 1360 1380 1400 Wavenumbers (cm-1)

48. 48 Foundation Series with multiple options

49. 49 Summary of ATR  Crystal type can be changed to adjust peak intensities of the sample  Very Easy, Fast, Non-Destructive Technique  Tremendous sample flexibility  Excellent for Quantitative Analysis - Constant Pathlength (assuming constant sample pressure)  Surface Studies (Shallow depth of penetration)  Can be configured for constant purge