stanford synchrotron radiation laboratory small angle scattering beam line for materials sciences...
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Stanford Synchrotron Radiation Laboratory
Small Angle Scattering Beam Line for Materials SciencesMike Toney & John Pople (SSRL)
1. Why new SAXS beam line?2. What, where & cost?3. Some examples
a. Fuel cell catalystsb. Particles on surfacesc. Polymers
4. Summary5. Appendix: (SAXS basics & how
proposal developed)
Materials Sciences SAXS Beam LineRequirements:• 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
SAXS Beam Line: Why?
• 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
• small angle scattering probes 1-100 nm length scales
• same length scales as nanoscale materials
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 cellssimultaneous SAXS/WAXS
bend magnetbetweenbeamlines4 and 5
focusingmirror (h & v)
mono:multilayers& Si(111)
SAXS detectorup 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
WAXSdetector
Specifications: • Focused flux ~ 1e12 h/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
slits: h & v
SAXS Beam Line: What
SAXS Beam Line: Where
• unused bending magnet• enough space for long hutch
between beam lines 4 (present) & 5Bending magnet satisfies most requirements; flux frequently not limiting factor
Sample environments:- furnace to ≈800o C- multi-sample holder (≈12) up to 200o C- chamber for windowless SAXS- grazing incidence-SAXS chamber
Estimated CostFront end & optics: $3.0MHutch (slits, detector): $0.7MSample environments: $0.3MTotal: $4.0M
bend magnetbetweenbeamlines4 and 5
focusingmirror (h & v)
mono:multilayers& Si(111)
SAXS detectorup to 5m flight path
WAXSdetector
slits: h & v
SAXS Beam Line: What & How Much
SAXS: Fuel Cell Catalysts
Goals: reduce cost: reduce Pt catalyst loading from present ~0.5mg/cm2
improve durability Membrane-Electrode Assembly
(PEM Fuel Cells)
Fuel Cells: Efficient conversion of chemical energy into electrical energy
Fundamental Breakthroughs needed:• reaction mechanisms• catalyst corrosion• activity/efficiency
Understanding properties of nanostructured electrocatalysts
SAXS: Fuel Cell Catalysts
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
Determine nanoparticle size distribution & changes during operation in Pt-alloys
4-2 with Strasser, Leisch, Koh, Fu
0.00
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0.80
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1.20
1.40
1.60
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0 2 4 6 8 10 12
Particle Diameter / nm
Pro
bab
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Pt edge L_C42 Pt edge C42 Pt edge L_C50 Pt edge C50 Pt edge L_ETEK Pt edge ETEK
Before testing
After corrosion
Particle Size
SAXS: Pt-M Alloy Catalysts
In-Situ SAXS: Fuel Cell Catalysts
In-Situ SAXS: Watch the Changing World
Monitor reaction progress: What are the changes accompanying a reaction? - corrosion (breaking bonds) - synthesis (making bonds)
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?
In-Situ SAXS Electrochemical Cell
Electrically Active Materials: Catalysts, medical implants, energy conversion
devices, electronics
Fuel Cell Catalysts:First Generation In-situ Cell
Nanoparticles on surfaces: gi-SAXS
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
Renaud et al., Science 300, 1416 (2003)
Nanoparticles on surfaces: gi-SAXS
Fe2O3 nanoparticles on surfaces• determine particle size and size distribution
YS Jun & Waychunas (LBL), Pople & Toney (SSRL)
New beam line• need large Q range• windowless slits & chamber• tune energy• dedicated chamber for gi-SAXS
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
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)
Materials Sciences SAXS Beam LineRequirements:• 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
Materials Science ReviewDirector'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.
Panel's RecommendationArea 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.
1. SAXS: 0.0007 Å-1 < q < 0.6 Å-1 2. WAXS: 0.6 Å-1 < q < 6 Å-1 3. Time resolution and timing4. Anomalous Scattering, 6 keV < E < 35 keV5. Range of spot sizes, as small as 10 μm2
6. Robotic sample control7. Temperature control from very cold to very hot8. Elevated gas pressures
• Measure I(Q) with Q 0.0001 – 1 Å-1
• Scattering from 1-100 nm density inhomogeneities
|Q| = (4)sin
k
incident
scatteredk’Q = k’ - k
Q
SAXS: Basics
SAXS: Basics
Isolated particlesor pores with diameter D
• Need large Q range: 1/D Q 10/D<~ <~
D
Q-4
Hexagonal packedcylinders
Huang et al, Appl. Phys. Lett. 81, 2232 (2002)
Nanoporous Films: SAXS
Find:• reasonably small pores (good)• board distribution of pore sizes
(bad)• size increases with loading =>
agglomeration (bad)