Stanford Synchrotron Radiation Laboratory

1. Stanford Synchrotron Radiation Laboratory Small Angle Scattering Beam Line for Materials Sciences Mike Toney & John Pople (SSRL) • Why new SAXS beam line? • What, where & cost? • Some examples • Fuel cell catalysts • Particles on surfaces • Polymers • Summary • Appendix: (SAXS basics & how proposal developed)

2. Materials Sciences SAXS Beam Line • Requirements: • simultaneous WAXS/SAXS • large Q range: • SAXS: Q ≈ 0.001 – 0.5 Å-1 • WAXS: Q ≈ 0.5 – 6 Å-1 • E = 5.9 - 20 keV • ca 0.1 x 0.5 mm2 spot size at detector • ca 0.1 sec time-scale • sample environments: furnaces, electrochemical cells, windowless chamber • near-surface facility (grazing incidence SAXS) • Science: • nanoparticles: metal alloy (fuel cells), oxides, minerals • polymers: fibrels, co-polymers • supramolecular assemblies • metallic glasses • nanoporous materials • colloids • particles on surfaces/films

3. SAXS Beam Line: Why? • small angle scattering probes 1-100 nm length scales • same length scales as nanoscale materials • nanoparticles • metal alloys for fuel cell catalysts • minerals & oxides • metals for nanowires • supramolecular assemblies • polymers • arborols and fibrels • phase transitions in co-polymers • metallic glasses • nanoporous materials • surface particles and thin films (giSAXS) • colloids (e.g., TiO2) • hydrogen storage materials

4. New SAXS Beam Line: Why? • need large Q range: dispersion in particle sizes & morphology reconstruction • windowless SAXS: weak scatterers • anomalous SAXS (tune energy): element specificity • reactions and phase transitions • real time measurements (ca 0.1 sec) • furnaces, reaction chambers, electrochemical cells • simultaneous SAXS/WAXS

5. SAXS Beam Line: What WAXS detector slits: h & v bend magnet between beamlines 4 and 5 mono: multilayers & Si(111) focusing mirror (h & v) SAXS detector up to 5m flight path • Sample environments: • furnace to ≈800o C • multi-sample holder (≈12) up to 200o C • stopped-flow cell • chamber for windowless SAXS • space for simultaneous optics & other instrumentation • heated shear cell • grazing incidence-SAXS chamber • Specifications: • Focused flux~1e12hn/s • E = 5.9 - 20 keV • 0.1 x 0.5 mm2 focus on detector • SAXS: Q ≈0.001 – 0.5 Å-1 • WAXS: Q ≈0.5 – 6 Å-1

6. SAXS Beam Line: Where between beam lines 4 (present) & 5 Bending magnet satisfies most requirements; flux frequently not limiting factor • unused bending magnet • enough space for long hutch

7. SAXS Beam Line: What & How Much WAXS detector slits: h & v bend magnet between beamlines 4 and 5 mono: multilayers & Si(111) focusing mirror (h & v) SAXS detector up to 5m flight path Estimated Cost Front end & optics: $3.0M Hutch (slits, detector): $0.7M Sample environments: $0.3M Total: $4.0M • Sample environments: • furnace to ≈800o C • multi-sample holder (≈12) up to 200o C • chamber for windowless SAXS • grazing incidence-SAXS chamber

8. Membrane-Electrode Assembly (PEM Fuel Cells) SAXS: Fuel Cell Catalysts • Goals: • reduce cost: reduce Pt catalyst loading from present ~0.5mg/cm2 • improve durability Fuel Cells: Efficient conversion of chemical energy into electrical energy • Fundamental Breakthroughs needed: • reaction mechanisms • catalyst corrosion • activity/efficiency • Understanding properties of nanostructured electrocatalysts

9. SAXS: Pt-M Alloy Catalysts After corrosion Before testing Particle Size SAXS: Fuel Cell Catalysts 4-2 with Strasser, Leisch, Koh, Fu Determine nanoparticle size distribution & changes during operation in Pt-alloys • Use SAXS to determine particle size • Problem: strong SAXS from carbon support • Solution: use anomalous SAXS • tune energy near Pt LIII edge and vary Pt scattering strength

10. In-Situ SAXS Electrochemical Cell Electrically Active Materials: Catalysts, medical implants, energy conversion devices, electronics In-Situ SAXS: Fuel Cell Catalysts In-Situ SAXS: Watch the Changing WorldMonitor reaction progress: What are the changes accompanying a reaction? - corrosion (breaking bonds) - synthesis (making bonds) Fuel Cell Catalysts: First Generation In-situ Cell When/how do the catalysts change during operation (corrosion, stability)? What effect does the structure have on the activity? How does this change over time of operation? Do better designs exist for a more robust material set?

11. Nanoparticles on surfaces: gi-SAXS • nanoparticles on surfaces or in films • precipitation • dissolution (pits) • templates • grazing incidence • (gi)-SAXS: • incidence angle < critical angle for total reflection • limit penetration into sample • near surface sensitivity gi-SAXS Renaud et al., Science 300, 1416 (2003)

12. Nanoparticles on surfaces: gi-SAXS • Fe2O3 nanoparticles on surfaces • determine particle size and size distribution • New beam line • need large Q range • windowless slits & chamber • tune energy • dedicated chamber for gi-SAXS YS Jun & Waychunas (LBL), Pople & Toney (SSRL)

13. Self-Assembly of Block Co-Polymers • Formation process of ordered domains in block co-polymers (Balsara group UCB); • oxidation state of redox-active species controls order • New Beam line • larger Q range • tune energy

14. Collaborators/beam line users • nanoparticles • fuel cell catalysts: Strasser (UHouston), Leisch (SSRL), • oxides: Bargar (SSRL), Gilbert (LBL), Waychunas (LBL), Sposito (UCB) • nanowires: Stevens (IRL, NZ), Ingham (SSRL) • supramolecular assemblies: Safinya (UCSB) • polymers • fibers: Balsara (UCB) • co-polymers: Russso (LSU) • metallic glasses: Huffnagel (Johns Hopkins) • nanoporous materials: Miller (IBM), Kim (IBM), Leisch (SSRL) • surface particles and thin films: Waychunas (LBL), Tolbert (UCLA) • colloids (e.g., TiO2): Strasser (UHouston), Gilbert (LBL) • hydrogen storage materials: Clemens (SU)

15. Materials Sciences SAXS Beam Line • Requirements: • simultaneous WAXS/SAXS • large Q range: • SAXS: Q ≈ 0.001 – 0.5 Å-1 • WAXS: Q ≈ 0.5 – 6 Å-1 • E = 5.9 - 20 keV • ca 0.1 x 0.5 mm2 spot size at detector • ca 0.1 sec time-scale • sample environments: furnaces, electrochemical cells, windowless chamber • near-surface facility (grazing incidence SAXS) • Science: • nanoparticles: metal alloy (fuel cells), oxides, minerals • polymers: fibrels, co-polymers • supramolecular assemblies • metallic glasses • nanoporous materials • colloids • particles on surfaces/films

16. Materials Science Review • Director's Materials Science Review - June 9-10, 2003 • Review of Opportunities with SPEAR3 exploring possible new initiatives in SSRL's chemical and materials science. • Sunil Sinha (UCSD, co-chair) • Russ Chianelli (UTEP, co-chair) • Franz Himpsel (Univ. of Wisconsin) • Bennett Larson (ORNL) • Simon Mochrie (Yale Univ.) • Cyrus Safinya (UCSB) • Sarah Tolbert (UCLA) • Don Weidner (SUNY). • The panel was charged with evaluating several proposed initiatives based on the increased performance of SPEAR3.

17. Panel's Recommendation • Area 1: Proposals that would have the most immediate impact on the materials synchrotron community. • Priority #1 – Super SAXS (ID beamline, wiggler) - A new full beamline with the following properties would have a great impact on the materials and biology community because of the simultaneous short range and long-range information obtained. • SAXS: 0.0007 Å-1 < q < 0.6 Å-1 • WAXS: 0.6 Å-1 < q < 6 Å-1 • Time resolution and timing • Anomalous Scattering, 6 keV < E < 35 keV • Range of spot sizes, as small as 10 μm2 • Robotic sample control • Temperature control from very cold to very hot • Elevated gas pressures

18. scattered k’ k incident 2q SAXS: Basics Q = k’ - k Q |Q| = (4p/l)sinq • Measure I(Q) with Q  0.0001 – 1 Å-1 • Scattering from 1-100 nm density inhomogeneities

19. p/D Q-4 • Need large Q range: • 1/D Q 10/D <~ <~ SAXS: Basics Isolated particles or pores with diameter D Hexagonal packed cylinders

20. Nanoporous Films: SAXS • Find: • reasonably small pores (good) • board distribution of pore sizes (bad) • size increases with loading => agglomeration (bad) Huang et al, Appl. Phys. Lett. 81, 2232 (2002)