Scattering Techniques and Geometries How to choose a beamline. Christopher J. Tassone

Transcription

1 Scattering Techniques and Geometries How to choose a beamline Christopher J. Tassone

2 Why Care About Geometries? How do you decide which beamline you want to use? Questions you should be asking Do I want to measure my sample in Transmission or Reflection Geometry? What do I want to know about my sample? Periodicity? Particle Size? Film Thickness? Surface Atom Arrangement? How it changes during operation? How crystalline is my sample? Single Crystalline? Polycrystalline? Textured? 2D Powder Where do the atoms in my sample absorb x-rays?

3 Beamline Overview Beamline & Detector Point Point & Area Area Area Advantages High resolution Accurate peak position and shape Weak peaks Variable energy High resolution Accurate peak position and shape Weak peaks Variable energy 6/4 degrees of motion Fast measurement Collect (nearly) whole pattern Fast measurement Looks at large features Variable Energy Lowest Background Disadvantages Slow Only 2 axes of motion Slow Can be difficult to find textured peaks Complicated Fixed wavelength Low resolution Peak shape and position less accurate Weak peaks difficult Small q range Background Sensitive Difficult Interpretation Methods Powders Thin Films Reflectivity θ-2θ Anomalous diffraction Single crystals Grazing-incidence Anomalous diffraction Surface studies Thin films Texture Real time experiments Polycrystalline, small grains Thin Films Real Time Experiments Solution Phase Transmission

4 Get to know your beamlines! Beamline 11-3 Energy =12.7 kev Detector - Mar 345 image plate Geometries - Transmission, Reflection Methods - Polycrystalline, small grains - Thin films - Texture (crystallite orientation) - Real time experiments (electrochemistry, stress-strain) Detector Q scattered incident

5 Get to know your beamlines! Beamline 1-5 Energy Range (4-20 kev) Flux = ph/sec low q limit = Å -1 (d 130 nm) Detector Fast CCD Image plate Geometries Transmission Reflection Phi-up Capillary

6 Get to know your beamlines! Beamline 7-2 Flux = 5 x ph/s Energy Range = 5-16 KeV Detectors - Pilatus 100K - Pilatus 300K - vortex - pmt Methods - High resolution diffraction - 2D WAXS - XRR - CTR - r-xrd

7 Get to know your beamlines! Beamline 10-2 Brightest line at SSRL - 1 x ph/s Detectors - Pilatus 100K - Pilatus 300K - Vortex Point Detector 4-c diffractometer Energy Range = kev Methods - 2D WAXS - PDF - CTR - r-xrd

8 Get to know your beamlines! Beamline 2-1 Dynamic Energy Range KeV Detectors - Vortex - PMT Methods - powder xrd - Reflectivity - Anomalous diffraction - θ-2θ measurements

9 X-ray Reflectivity Basics 2q k k q Q = k - k Q = (4p/l)sin q What we get from XRR Film Thickness Film Roughness Material Density

10 X-ray reflectivity Which Beamline and Why? Energy range 4->30 kev Potentially Larger Background Heavily subscribed Energy Range 5->18keV Capable of running WAXS & XRR Temperature Controlled Higher Background Complicated Energy range 4->13 kev Capable of running p- XRD & XRR Environmental Chamber Lower brightness

11 2D WAXS What Can WAXS Tell Us? Molecular Packing 2D grazing incidence: Peak Positions Crystallite Size Peak FWHM Relative Degree of Crystallinity Integrated Peak Intensity Crystallite Orientation Peak Intensity vs. Polar Angle (χ) sample 2D image plate

12 2D WAXS Which Beamline and Why? Need large q-range Don t need time resolution 12.7 kev photons work Smaller q-range alright Partial diffraction arcs/highly textured samples Need time resolution Energy range 4->16 kev Extra 2 degrees of freedom Smaller q-range alright Partial diffraction arcs/highly textured samples Need time resolution Energy range 4->30 kev

13 Powder Diffraction 2q scattered k incident k Q = k - k Q = (4p/l)sin q What p-xrd Tells You Lattice; unit cell size & strain; crystallite orientation Phase identification & quantify Where are the atoms: atomic/crystal structure Grain/crystallite size; defects & disorder Sample Choices Flat plate vs. Capillary

14 Powder Diffraction Which Beamline and Why? Need large q-range Need minute time resolution 12.7 kev photons work Lowest Resolution Transmission or flat plate geometry Time resolution not needed Energy range 4->18 kev High resolution data desired Flat plate or Transmission Time resolution not needed Energy range 4->14.;5 kev Environmental Chamber High resolution data Capillary Spinner

15 Powder Diffraction Slit Concerns: Crystal Analyzer or No? Several Slit Options Available Crystal Analyzer Soller Slits Programmable Slits 2q k k q Q = k - k Q = (4p/l)sin q

16 CTR reciprocal space L ideal (bulk-termination) relaxed crystal top layer expanded (L) real space Elements of modern X-ray physics (2 nd ed.) Jens Als-Nielsen & Des McMorrow.

17 CTR Which Beamline and Why? 7-2 is your only choice!

18 r-xrd Resonant Diffraction Element specific Change in atomic scattering power near absorption edges Quantify site disorder and stoichiometry 2q k q k Q = k - k Q = (4p/l)sin q

19 r-xrd Which Beamline and Why? Energy range 4->30 kev 4C-Diffractometer Transmission or reflection Energy range 4->18 kev 6-c diffractometer Transmission or reflection Energy range 4->14.5 kev 2-c diffractometer Capillary spinner

20 SAXS scattered Q 2q k incident k Scattering from nm density inhomogeneities

21 SAXS at 1-5 Q-ranges 1 meter flight path: Å -1 > q > 0.67 Å nm > d > 4 nm 3 meter flight path: 0.001Å -1 > q > 0.22 Å nm > d > 14 nm Sample Environments Transmission Reflection Capillary Heating stage Energy Range 4-16 kev

22 Questions for Users What method do I want to use? What detector do I want to use? What q-range am I interested in? What angular resolution do I need? What energy do I want to work at? How strongly does my system scatter?

23 Talk to the Beamline Scientists and Engineers Chad Miller (7-2, 2-1, 1-5, 11-3) Ronald Marks (7-2) Apurva Mehta (7-2,10-2, 2-1) Christopher Tassone (11-3, 1-5) edu Valery Borzenets (10-2) Doug VanCampen (11-3)