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The world leader in serving science Reflection Techniques.

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Presentation on theme: "The world leader in serving science Reflection Techniques."— Presentation transcript:

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  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 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, cm -1, RI-2.2)  Diamond (4, cm -1, RI-2.4)  ZnSe (20, cm -1, RI-2.4)  Si (8, cm -1, RI-3.4)  Ge (5, 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 = Absorbance Wavenumbers (cm -1 )

40 40 D p vs. frequency Sample R.I Ge(4.0 RI) ZnSe(2.4 RI)  m*  m*  m*  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 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 Absorbance 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


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