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

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0 2 4 6 8 10 12

Particle Diameter / nm

Pro

bab

ilit

y

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)