X-ray Diffraction and EBSD

Transcription

1 X-ray Diffraction and EBSD Jonathan Cowen Swagelok Center for the Surface Analysis of Materials Case School of Engineering Case Western Reserve University October 27, 2014

2 Outline X-ray Diffraction (XRD) History and background Introduction to XRD Practical applications Electron Back-Scattered Diffraction (EBSD) Introduction to EBSD Types of information that can be drawn from EBSD

3 Discovery of X-rays and Modern XRD Wilhelm Conrad Röntgen 1895: Discovery of X-ray 1901: awarded first Nobel prize winner for Physics M.T.F. von Laue: 1912: Discovery of the diffraction of X-rays by single crystals, in cooperation with Friedrich and Knipping Terms: Laue equation, Laue reflections 1914: Nobel prize for Physics W.H. and W.L. Bragg: 1914: X-ray diffraction and Crystal Structure Terms: Bragg s equation, Bragg reflections 1915: Nobel prize for Physics

4 X-ray Generation Cathode e - X-rays Anode K α =1.54Å Intensity K β =1.39Å Wavelength (Å) The emission spectra for Cu

5 Monochromatic Radiation is needed for Crystal Intensity Mass Absorption Coefficient K β K α K β K α Structure Analysis Filters for Suppression of K β Radiation λ(å) Unfiltered λ(å) Ni Filter The dotted line is the Mass Absorption coefficient for Ni

6 Interference and Bragg s Law AO=OB Bragg Diffraction occurs when 2AO=nλ Sinθ=AO/d(hkl) 2d Sinθ=nλ λ=wavelength of the incident radiation Cu Kα=1.54 Å

7 Monochromatic X-rays using Diffraction Graphite monochromator utilizes a highly orientated pyrolytic graphite crystal (HOPG) mounted in a compact metal housing to provide monochromatic radiation. This is usually an improvement over filters. C (Graphite)

8 Lattice Parameter Calculation Miller Indices Bragg s Law Silicon Powder Knowing d hkl we can calculate the lattice parameters

9 X-ray Diffraction Differentiate Crystal Structures C (Graphite) C (Diamond) SiC nm

10 Scintag Advanced X-Ray Diffractometer System Conventional theta-theta scan Rocking curves and sample-tilting curves Grazing angle X-ray diffraction (GAXRD) DMSNT software package is used to control the diffractometer, to acquire raw data and to analyze data. PDF-2 database and searching software for identifying phases

11 X-ray Diffraction Typical Patterns Amorphous Pattern Crystalline Pattern Amorphous patterns will show an absence of sharp peaks Crystalline patterns will show many sharp peaks The atoms are very carefully arranged High symmetry From peak locations and Bragg s Law, we can determine the structure and lattice parameters. Elemental composition is never measured By comparing to a database of known materials, phases can be identified

12 X-ray Diffraction Peak Intensities 1. Polarization Factor 2. Structure Factor 3. Multiplicity Factor 4. Lorentz Factor 5. Absorption Factor 6. Temperature Factor α-al 2 O 3

13 Iron Chloride Dihydrate X-ray Diffraction Phase Identification International Centre for Diffraction Data (ICDD) The PDF-2 (Powder Diffraction File) database contains over 265K entries. Modern computer programs can determine what phases are present in any sample by quickly comparing the diffraction data to all of the patterns in the database. The PDF card for an entry contains much useful information, including literature references.

14 X-ray Diffraction Phase Identification PDF # Iron Chloride Hydrate Iron Chloride Dihydrate

15 X-ray Diffraction Quantitative Phase Analysis (QPA) External standard method A reflection from a pure component. Direct comparison method A reflection from another phase within the mixture. Internal standard method A reflection from a foreign material mixed within the sample. Reference Intensity Ratio (RIR) Generalized internal standard method developed by the ICDD. Breakdown of the PDF-2 database

16 X-ray Diffraction Quantitative Phase Analysis (QPA) DIFFRAC.SUITE EVA Fe 75, Ni 25 wt.%

17 X-ray Diffraction X ray diffraction of semi-crystalline polymer and amorphous polymer

18 X-ray Diffraction XRD is a primary technique to determine the degree of crystallinity in polymers. The determination of the degree of crystallinity implies use of a two-phase model, i.e. the sample is composed of crystalline and amorphous regions.

19 Smaller Crystals Produce Broader XRD Peaks 2nm Gold Nanoparticle Note: In addition to instrumental peak broadening, other factors that contribute to peak broadening include strain and composition inhomogeneities.

20 When to Use Scherrer s Formula Crystallite size < 5000 Å t = K λ B cosθ B t = thickness of crystallite K = constant dependent on crystallite shape (0.89) λ = X-ray wavelength B = FWHM (full width at half max) or integral breadth θ B = Bragg angle

21 Residual Stress Measurements using X-Ray Diffraction

22 X-ray Diffraction Diffraction cones arise from randomly oriented polycrystalline aggregates or powders X-ray Polycrystalline Sample Diffraction Cone forms Debye Rings

23 X-ray Diffraction 2D Detector Area Detector Debye Rings

24 Scintillation detector X-ray Diffraction Types of Detectors 2D Area detector Small portion of Debye ring acquired scan necessary long measuring times large 2θ and chi range measured simultaneously measurement of oriented samples very short measuring times intensity versus 2θ by integration of the data

25 X-ray Diffraction Bruker D8 Discover Small Beam diameter Can achieve 200μm Parallel Illumination Forgives displacement errors 4 circle Huber goniometer Dual beam alignment system

26 X-ray Diffraction Orientation Polymers, due to their long chain structure, are often highly oriented. Alignment of a sample in a drawing process causes orientation effects

27 X-ray Diffraction Orientation The intensity distribution of the Debye ring reveals much information about the texture of the material being studied!

28 X-ray Diffraction of Conch Shells In addition to identifying the CaCO 3 as the Aragonite polymorph, X-ray diffraction patterns reveal a strong degree of crystallographic texture in the intact shell.

29 X-ray Diffraction Orientation Simulated pattern of CuInSe Acquired XRD pattern of a thin film of CuInSe 2 grown on a Mo foil substrate

30 Rigaku D/MAX 2200 Diffractometer X-ray Sources Anode Kα 1 (Å) Cu Cr Co Comments Best for inorganics. Fe and Co fluorescence. High Resolution for large d- spacing. High attenuation in air. Used for ferrous alloys to reduce Fe fluorescence.

31 X-ray Diffraction Summary Structure Determination Phase Identification Quantitative Phase Analysis (QPA) Percent Crystallinity Crystallite Size and Microstrain Residual Stress Measurements (Macrostrain) Texture Analysis Single Crystal Studies (not a SCSAM core competency)

32 Electron Diffraction Zeiss Libra 200EF Polycrystal Single Crystal

33 EBSD Electron Back-Scattered Diffraction in the SEM Background Corrected Pattern Averaged Background Raw Pattern

34 EBSD Electron Back-Scattered Diffraction in the SEM Background Corrected Pattern Indexed Pattern

35 EBSD data Maps Beam scan provides orientation map of polycrystalline NaCl grid 5 μm step Analysis time: 36 minutes The colors indicate specific orientations 500 μm

36 polycrystalline Al 2 O 3 EBSD data Maps

37 A single automated EBSD run can provide a complete characterization of the microstructure: Phase distribution Texture strength Grain size Boundary properties Misorientation data Slip system activity Intra-granular deformation Can collect XEDS simultaneously

38 EBSD Phase Discrimination bcc Fe fcc Fe Differences in interplanar angles and spacings allow similar-looking EBSD patterns from bcc and fcc Fe to be readily distinguished. bcc Fe fcc Fe

39 EBSD data Maps Phase distribution, texture, grain size / shape, boundary properties, misorientation, slip system activity, intra-granular deformation... Phase map Orientation bcc Orientation fcc

40 Summary XRD is a powerful tool for answering some specific questions about a given sample. Phases present, QPA, orientation, residual stress, texturing, and crystallite size analysis. XRD is extremely efficient for the characterization of samples. Sample preparation time is minimal when compared to SEM/EBSD and TEM. Data acquisition is straight forward and short set up times are required. XRD will provide a larger sampling area and a more accurate averaged result of the lattice parameter, but EBSD will be more site specific. EBSD yields similar results and all the same specific questions can be answered in one data set!

41 Hough Transformation Hough transformation Transforms x-y space to ρ θ space. Bands in Hough space show as points which are easier to identify and extract

42 Format of Crystal Information Solution # Band triplets # votes S3 (best solution w/most votes) S2 (2 nd best solution w/ 2 nd most votes) Euler Angles using Bung convention: 1. A rotation of φ 1 about the z axis followed by 2. A rotation of ϕ about the rotated x- axis followed by 3. A rotation of φ 2 about the rotated z- axis

43 X-ray Diffraction Phase Identification

44 Intensity Mass Absorption Coefficient K β K α K β K α λ(å) Unfiltered λ(å) Ni Filter