Total Scattering The Key to Understanding disordered, nanocrystalline and amorphous materials. Tutorial 9th Canadian Powder Diffraction Workshop Thomas Proffen Diffraction Group Leader tproffen@ornl.gov Friday 25th May 2012 9:00 - 9:45 9:45 - 10:30 Beyond the Bragg peaks or why do we care about total scattering? Measuring total scattering X-ray and neutron data: where and how? 10:30 - 11:15 Break 11:15-12:30 What to do with your PDF: Modeling of disordered structures ? 12:30 - 1:30 Lunch 1:30 - 5:00 Practical Sessions All cartoons by Julianne Coxe. 2 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Measuring Total Scattering 3 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Experimental Considerations 4 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. How to obtain high quality PDFs ? The PDF (similar to the Patterson) is obtained via Fourier transform of the normalized total scattering S(Q): G(r ) 2 Q[ S (Q ) 1]sin(Qr )dQ 0 Requirements to obtain ‘good’ PDF: High maximum momentum transfer, Qmax. High Q-resolution. Good counting statistics @ high Q. Low instrument background Where ? Synchrotron sources (high energy X-rays) 5 Managed by UT-Battelle for the U.S. Department of Energy or spallation neutron sources (reactor neutron energies are too low) 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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): G (r ) 2 Q[S (Q) 1]sin(Qr )dQ 0 Requirements to obtain ‘good’ PDF: High maximum momentum transfer, Qmax. High Q-resolution. Good counting statistics @ high Q. Low and stable instrument background. 6 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. DISCUS - http://discus.sourceforge.net/ 3 day DISCUS workshop in Spring 2012 in Erlangen, Germany .. 7 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Q resolution Ni data from GLAD (IPNS) and high resolution NPDF (Lujan) 8 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Q resolution .. 9 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Nanoparticles: Particle size Nanogold Spherical particle envelope 3 3 r 1 r 1 2 R 2 R 10 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Experimental Facilities or Where to measure a good PDF ? Neutrons 11 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 12 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 ! 13 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 14 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutrons vs. X-rays • Sensitive to light atoms (e.g. H) • Contrast by isotope substitution X-ray and neutron scattering Lengths for selected elements. • Easy sample environment (T,p,..) • No ‘formfactor’ (good for PDF) • Weak large samples & long measuring times .. Scattering from single atom 15 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Time of Flight Diffraction I ki res = bw kf Neutron Source Spectrum bw T ki kf I I res T Angle dispersive: Vary scattering angle in Bragg’s law Energy dispersive: Vary wavelength (TOF – wavelength) 16 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 17 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. SNS – how does it work ? 18 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Spallation Neutron Source Powder diffractometers • POWGEN : High resolution • NOMAD: Total scattering • VULCAN: Engineering 19 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. NOMAD contact • Total scattering instrument • Science of disordered materials, glasses and nanomaterials • Commissioning – partial user program 20 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Jorg Neuefeind neuefeindjc@ornl.gov Mikhail Feygenson feygensonm@ornl.gov 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 21 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 22 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. LANSCE: Multiple experimental areas Isotope production Facility Proton Radiography Ultracold Neutrons Materials Test Station PSR Target 1L Target 2 Target 4 (WNR) 23 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Lujan Center ER-1/2 Lujan Center: Powder diffractometers 24 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 25 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. The ISIS Neutron Facility 26 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. ISIS: Powder diffractometers • GEM • POLARIS Sample tank • SANDALS Incident Polychromatic Neutron Beam Bank 6 142-169o Bank 1 6-13o 27 Managed by UT-Battelle for the U.S. Department of Energy Bank 2 14-21o Bank 3 25-45o Bank 4 50-75o 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Bank 5 79-104o 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. January 2010: Yumiko Nakamura opens shutter of NOVA shutter during first joined LANLAIST experiment. The instruments provide complementary total scattering data. LANL collaborators are the first external users of NOVA (January 2010) Instrument scientist: T. Otomo 28 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Experimental Facilities or Where to measure a good PDF ? X–rays 29 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Synchrotron sources 30 Managed by UT-Battelle for the U.S. Department of Energy http://www.esrf.eu/AboutUs/GuidedTour/ 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray PDF: The traditional way 100 (2% ~) C om pton + Elastic (~98% ) 80 60 40 In te n s ity (a .u .) 20 Intensity, a.u. 25 20 -1 Q = 2 (Å ) 0 80 (85% ~) C om pton 60 Elastic (~15% ) 40 20 -1 Q = 25 (Å ) 0 15 C om pton (~97% ) 80 10 60 40 5 -1 Q = 40 (Å ) 0 0 0 5 10 15 20 25 30 35 40 -1 Q (Å ) 31 Elastic (~3% ) 20 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 60 70 80 90 100 E [keV] Valeri Petkov 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 32 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray PDF: The fast way Exposure: 25 sec ! Image plate detector P.J. Chupas, X. Qiu, J.C. Hanson, P.L. Lee, C.P. Grey and S.J.L. Billinge, Rapid-acquisition pair distribution function (RAPDF) analysis, J. Appl. Cryst. 36, 1342-1347 (2003). 33 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 11ID-B at the Advanced Photon Source Application of a large-area, highsensitivity, fast readout, flat-panel GE detector based on amorphous silicon. PDF acquisition at 30Hz ! Time-resolved PDF measurements: Reduction of PtIV Pt0 P. Chupas et al, J. Appl. Cryst. 40, 463-470 (2007). 34 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 35 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Agreement between LANL and ANL .. 36 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. MgCo – the power of neutrons and x-rays PDF peak intensity ∝ where bi is the scattering length of the ith atom. 37 bi for x-ray bi for neutron Mg 12 3.631 Co 27 0.779 bmbn Mg-Mg Mg-Co Co-Co x-ray 144 324 729 neutron 13.18 2.83 0.607 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray PDF: In house measurements fci-Ho-Mg-Zn Huber Gunier diffractometer Qmax = 13.5Å-1 Brühne et al., Z. Kristallogr. 219 (2004) 245-258 38 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray PDF: In house measurements • STOE STADI-P diffractometer • Cu Kα1 radiation (Qmax = 6.5 A-1) • Data collection time: 27 h • Why Cu? – Information on average structure (→ Structure solution) Naphthalene: 2.8 Å ≈ 7Å Raw data: PDF: C10H8 39 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 2.4 Å Buy your own PDF diffractometer .. Exhibit at the EPDIC meeting 2008 (Photo by Nadine Rademacher) 40 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Data Reduction How difficult is the processing of total scattering data ? 41 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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] 42 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. G (r ) 2 0 Q[ S (Q) 1] sin QrdQ Neutron corrections • TOF Q conversion • Deadtime correction • Absorption Conversion from time of flight to Q depends on path lengths. Can be refined, e.g. GSAS: TOF = DIFC d + DIFA d2 + T0 • Multiple scattering • Normalization • Placzek correction • Parasitic scattering DIFC 252 .816 2 sin L1 L22 L23 / 16 L1: primary flight path (source – sample) L2: secondary flight path (sample – detector) L3: detector height 43 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 deadtime are not recorded. Count-rate dependent. Important at high count-rates. Corrected analytically. 44 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutron corrections • TOF Q conversion • Deadtime correction • Absorption Depends on wavelength and elements present. • Multiple scattering • Normalization • Placzek correction • Parasitic scattering 45 Managed by UT-Battelle for the U.S. Department of Energy Depends on path sample PDFgetN corrects for cylindrical geometry ! 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutron corrections • TOF Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Placzek correction • Parasitic scattering 46 Managed by UT-Battelle for the U.S. Department of Energy Neutrons that are scattered twice or more in the sample need to be corrected. Effect can be as big as 10% ! Corrected theoretically. 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutron corrections • TOF Q conversion • Deadtime correction Incident beam is monitored to normalize for the total neutron flux. • Absorption Incident neutron spectrum is corrected via vanadium characterization run. • Multiple scattering • Normalization • Placzek correction • Parasitic scattering 47 Managed by UT-Battelle for the U.S. Department of Energy The condition S(Q) 1 for high Q is used to normalize for sample size and density. 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutron corrections • TOF Q conversion • Deadtime correction • Absorption Inelastically scattered neutrons are counted in the incorrect Q-bin in the time of flight neutron method. • Multiple scattering Corrected theoretically (?) • Normalization • Placzek correction Strictly only valid for liquids. • Parasitic scattering Needs new approach ! 48 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Neutron corrections • TOF Q conversion • Deadtime correction • Absorption Measured (background and empty can) and subtracted after suitable normalization. • Multiple scattering • Normalization • Placzek correction • Parasitic scattering 49 Managed by UT-Battelle for the U.S. Department of Energy Reproducible background key to success ! 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. 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 50 Managed by UT-Battelle for the U.S. Department of Energy P.F. Peterson, M. Gutmann, Th. Proffen and S.J.L. Billinge, PDFgetN: A User-Friendly Program .., J. Appl. Cryst. 33, 1192 (2000). 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray data processing • In house X-ray experiments: – Easy. – Low r resolution, slow (and/or poor statistics). – Mo: Qmax ~ 17Å-1, Ag: Qmax ~ 20Å-1. – Flat plate transmission or reflection geometry. Transmission (transparent samples) Reflection (absorbing samples) • Synchrotron experiments: – Little precious beamtime. – High energy X-rays (Qmax > 60Å-1). – High intensity (x 10,000 times stronger). – Parallel beam optics. – Generally flat plate transmission geometry. – New rapid PDF setup (PDF in seconds). 51 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray corrections • 2 Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Compton scattering • Polarization correction Data from some diffractometers might require a conversion from scattering angle 2 to momentum transfer Q ! Uncertainties: Offset 2, wavelength • Parasitic scattering 52 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray corrections • 2 Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Compton scattering • Polarization correction • Parasitic scattering 53 Managed by UT-Battelle for the U.S. Department of Energy Incident beam is monitored to normalize for the total X-ray flux (especially at the synchrotron). Normalization for angle depended change of illuminated sample volume. The condition S(Q) 1 for high Q is used to normalize for sample size and density. 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray corrections • 2 Q conversion • Deadtime correction • Absorption Compton scattering is inelastic incoherent scattering. • Multiple scattering • Normalization • Compton scattering Calculated theoretically or measured and subtracted. • Polarization correction • Parasitic scattering 54 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray corrections • 2 Q conversion • Deadtime correction • Absorption • Multiple scattering • Normalization • Compton scattering • Polarization correction Intensity depends on beam polarization which depends on beamline optics (monochromators etc.) and angle. • Parasitic scattering 55 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. X-ray corrections: Removal of Compton scattering Energy sensitive detector (e.g. Ge detector) allows separation of Compton scattering at higher Q. Q=40Å-1 Modes: SCA: Electronic windows to separate elastic channel MCA: recording of complete spectrum at each measured point software integration. 56 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon. Software: PDFgetX2 X. Qiu, J.W. Thompson, S.J.L. Billinge, J. Appl. Cryst. 37, 678-678 (2004) • Use Fit2D for area detector integration. • Reads SPEC files. • Supports MCA and SCA data. • Integrated plotting of various corrections applied. • Tools for merging scans. • Runs on Windows and UNIX. Based on IDL (download free runtime environment). http://www.pa.msu.edu/cmp/billinge-group/programs/PDFgetX2/ 57 Managed by UT-Battelle for the U.S. Department of Energy 9th Canadian Powder Diffraction Workshop – May 23-25, 2012 University of Saskatchewan, Saskatoon.