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Thomas Proffen Diffraction Group Leader tproffen@ornl.gov

Total Scattering The Key to Understanding disordered, nano -crystalline and amorphous materials. Tutorial 9 th Canadian Powder Diffraction Workshop. Thomas Proffen Diffraction Group Leader tproffen@ornl.gov. Friday 25th May 2012. All cartoons by Julianne Coxe . Measuring Total

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Thomas Proffen Diffraction Group Leader tproffen@ornl.gov

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  1. Total Scattering The Key to Understanding disordered, nano-crystalline and amorphous materials.Tutorial9th Canadian Powder Diffraction Workshop Thomas Proffen Diffraction Group Leader tproffen@ornl.gov

  2. Friday 25th May 2012 All cartoons by Julianne Coxe.

  3. Measuring Total Scattering

  4. Experimental Considerations

  5. Where ? Synchrotron sources or spallation neutron sources (high energy X-rays) (reactor neutron energies are too low) How to obtain high quality PDFs ? The PDF (similar to the Patterson) is obtained via Fourier transform of the normalized total scattering S(Q): • Requirements to obtain ‘good’ PDF: • High maximum momentum transfer, Qmax. • High Q-resolution. • Good counting statistics @ high Q. • Low instrument background

  6. NPDF: the key to high quality, high r PDFs The PDF (similar to the Patterson) is obtained via Fourier transform of the normalized total scattering S(Q): • Requirements to obtain ‘good’ PDF: • High maximum momentum transfer, Qmax. • High Q-resolution. • Good counting statistics @ high Q. • Low and stable instrument background.

  7. DISCUS - http://discus.sourceforge.net/ 3 day DISCUS workshop in Spring 2012 in Erlangen, Germany ..

  8. Q resolution Ni data from GLAD (IPNS) and high resolution NPDF (Lujan)

  9. Q resolution ..

  10. Nanoparticles: Particle size Nanogold Instrument resolution Spherical particle envelope

  11. Experimental Facilities or Where to measure a good PDF ? N e u t r o n s

  12. Facility overview • Spallation Neutron Sources • Lujan Neutron Scattering Center, Los Alamos, USA • ISIS Pulsed Neutron and Muon Facility, Didcot, UK • IPNS, Argonne, USA – closed • Spallation Neutron Source, Oak Ridge, USA • Japan Proton Accelerator Research Complex, Tokai, Japan • Synchrotron Sources • Advanced Photon Source, Argonne, USA • ESRF, Grenoble, France • Many more .. • Links • http://neutron.anl.gov/facilities.html • http://www-als.lbl.gov/als/synchrotron_sources.html

  13. Facility Access • Most facilities in the US (and Europe) run a open user program. • Peer reviewed proposals. • Tips for success: • Check the facilities web sites. • Contact the instrument scientist before submitting a proposal online !

  14. Neutrons ? Neutrons show where the atoms are…. The 1994 Nobel Prize in Physics – Shull & Brockhouse …and what the atoms do. Wave nature of neutron: de Broglie relation: =h/p

  15. Neutrons vs. X-rays • Sensitive to light atoms (e.g. H) • Contrast by isotope substitution • Easy sample environment (T,p,..) • No ‘formfactor’ (good for PDF) • Weak  large samples & long measuring times .. X-ray and neutron scattering Lengths for selected elements. Scattering from single atom

  16. Time of Flight Diffraction Neutron Source Spectrum I l Angle dispersive: Vary scattering angle in Bragg’s law Energy dispersive: Vary wavelength (TOF – wavelength)

  17. Neutrons at Oak Ridge National Lab. ORNL hosts two neutron sources: • Spallation Neutron Source • High Flux Isotope Reactor • Both are DOE User Facilities • Also hosts the Joined Institute for Neutron Sciences http://neutrons.ornl.gov

  18. SNS – how does it work ?

  19. Spallation Neutron Source Powder diffractometers • POWGEN : High resolution • NOMAD: Total scattering • VULCAN: Engineering

  20. contact • Jorg Neuefeind • neuefeindjc@ornl.gov • Mikhail Feygenson • feygensonm@ornl.gov NOMAD • Total scattering instrument • Science of disordered materials, glasses and nano-materials • Commissioning – partial user program

  21. NOMAD opens the door to ‘x-ray size’ samples of less than 1mg. Overnight run on NOMAD • Diffraction of small Samples • Studies of rare and/or expensive samples • Example Na35Cl • Isotopic labeling for local structure • High cost for stable isotopes • Well-defined structure with less than 1mg

  22. NOMAD: Isotope substitution experiment CaSiO3 melt L. Skinner, C.J. Benmore, J.K.R. Weber, S. Tumber, L. Lazareva, J. Neuefeind, L. Santodonato, J. Du, J.B. Parise

  23. LANSCE: Multiple experimental areas Ultracold Neutrons Isotope production Facility Proton Radiography Materials Test Station PSR Target 1L Target 2 Target 4 (WNR) Lujan Center ER-1/2

  24. Lujan Center: Powder diffractometers

  25. NPDF: Overview • Specifications • Upgrade finished Sep. 2002 • L1: 32m, Qmax=50Å-1, d/d=0.15% • Typical PDF measurement 1 - 4 hrs • Sample amounts down to 200 mg • Ancillary: 10K-1500K, soon: 0.5K, 11T • Science • 95% PDF studies, hard matter • Many users new to PDF • Software • Web based instrument interface • Automatic creation of PDF • Integration in SNS data portal (soon) • http://www.lansce.lanl.gov

  26. The ISIS Neutron Facility

  27. Incident Polychromatic Neutron Beam Sample tank Bank 6 142-169o Bank 5 79-104o Bank 3 25-45o Bank 4 50-75o Bank 2 14-21o Bank 1 6-13o ISIS: Powder diffractometers • GEM • POLARIS • SANDALS

  28. Instrument: NOVA at J-PARC NPDF at LANSCE is a high resolution total scattering instrument. NOVA constructed at J-PARC as part of the HYDRO-STAR project is a high flux total scattering spectrometer. The instruments provide complementary total scattering data. LANL collaborators are the first external users of NOVA (January 2010) January 2010: Yumiko Nakamura opens shutter of NOVA shutter during first joined LANL-AIST experiment. Instrument scientist: T. Otomo

  29. Experimental Facilities or Where to measure a good PDF ? X – r a y s

  30. Synchrotron sources http://www.esrf.eu/AboutUs/GuidedTour/

  31. X-ray PDF: The traditional way Valeri Petkov

  32. X-ray PDF: The traditional way • Energy dispersive detector • Step scans in Q • Long counting times, especially at high Q. • Typical collection time: 12-24 h

  33. X-ray PDF: The fast way Image plate detector Exposure: 25 sec ! P.J. Chupas, X. Qiu, J.C. Hanson, P.L. Lee, C.P. Grey and S.J.L. Billinge, Rapid-acquisition pair distribution function (RA-PDF) analysis, J. Appl. Cryst.36, 1342-1347 (2003).

  34. 11ID-B at the Advanced Photon Source Application of a large-area, high-sensitivity, fast readout, flat-panel GE detector based on amorphous silicon. PDF acquisition at 30Hz ! Time-resolved PDF measurements: Reduction of PtIV Pt0 P. Chupaset al, J. Appl. Cryst. 40, 463-470 (2007).

  35. 11ID-B at the Advanced Photon Source Beamline Specs Source 2.3 Undulator Monochromator Type Si(511) Energy Range 90-91 keV Resolution (ΔE/E) 1 x 10 -3 Flux (photons/sec) 1 x 10 11 @90 keV Beam Size (HxV) Unfocused 1mm x 1mm Monochromator Type Si(311) Energy Range 58-60 keV Resolution (ΔE/E) 1 x 10 -2 Flux (photons/sec) 1 x 10 11 @58 keV Beam Size (HxV)  Unfocused 1mm x 1mm

  36. Agreement between LANL and ANL ..

  37. PDF peak intensity ∝ where bi is the scattering length of the ith atom. MgCo – the power of neutrons andx-rays

  38. X-ray PDF: In house measurements Huber Gunier diffractometer Qmax = 13.5Å-1 fci-Ho-Mg-Zn Brühne et al., Z. Kristallogr.219 (2004) 245-258

  39. 1.4Å 2.8Å 2.4Å 1.1Å C10H8 X-ray PDF: In house measurements • STOE STADI-P diffractometer Naphthalene: • Cu Kα1 radiation (Qmax = 6.5A-1) • Data collection time: 27h • Why Cu? • Information on average structure(→ Structure solution) ≈ 7Å Raw data: PDF:

  40. Buy your own PDF diffractometer .. Exhibit at the EPDIC meeting 2008 (Photo by Nadine Rademacher)

  41. Data Reduction How difficult is the processing of total scattering data ?

  42. Neutron data processing Corrections • Cylindrical Time-Of-Flight geometry (energy dispersive) • Typical characterization runs • Empty instrument (B) • Empty Container (C) • Empty Container background (CB) • Vanadium (V) • Vanadium background (VB) • Sample (S) • Scorr=[(S-SB)-(C-CB)]/[V-VB]

  43. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering Conversion from time of flight to Q depends on path lengths. Can be refined, e.g. GSAS: TOF = DIFC d + DIFA d2 + T0 L1: primary flight path (source – sample) L2: secondary flight path (sample – detector) L3: detector height

  44. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • After an event is recorded the detector generally needs some time to reset itself and the detector electronics to process the pulse. Neutrons arriving during this dead-time are not recorded. • Count-rate dependent. • Important at high count-rates. • Corrected analytically.

  45. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • Depends on wavelength and elements present. • Depends on path sample  PDFgetN corrects for cylindrical geometry !

  46. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • Neutrons that are scattered twice or more in the sample need to be corrected. • Effect can be as big as 10% ! • Corrected theoretically.

  47. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • Incident beam is monitored to normalize for the total neutron flux. • Incident neutron spectrum is corrected via vanadium characterization run. • The condition S(Q)  1 for high Q is used to normalize for sample size and density.

  48. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • Inelastically scattered neutrons are counted in the incorrect Q-bin in the time of flight neutron method. • Corrected theoretically (?) • Strictly only valid for liquids. • Needs new approach !

  49. Neutron corrections • TOF  Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering • Measured (background and empty can) and subtracted after suitable normalization. • Reproducible background key to success !

  50. Software: PDFgetN • Based on GLASS package. • Graphical users interface & integrated plotting. • Supports most TOF neutron powder file formats. • Records all processing parameters as part of output files G(r) and S(Q). • Runs on Windows 95/98/NT/2000 and UNIX http://pdfgetn.sourceforge.net P.F. Peterson, M. Gutmann, Th. Proffen and S.J.L. Billinge, PDFgetN: A User-Friendly Program .., J. Appl. Cryst.33, 1192 (2000).

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