Transcript Stanford Synchrotron Radiation Laboratory Small Angle Scattering Beam Line for Materials Sciences Mike Toney & John Pople (SSRL) 1.

Stanford Synchrotron Radiation Laboratory
Small Angle Scattering Beam Line
for Materials Sciences
Mike Toney & John Pople (SSRL)
1. Why new SAXS beam line?
2. What, where & cost?
3. Some examples
a. Fuel cell catalysts
b. Particles on surfaces
c. Polymers
4. Summary
5. Appendix: (SAXS basics & how
proposal developed)
Materials Sciences SAXS Beam Line
Science:
• nanoparticles: metal alloy (fuel
cells), oxides, minerals
• polymers: fibrels, co-polymers
• supramolecular assemblies
• metallic glasses
• nanoporous materials
• colloids
• particles on surfaces/films
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)
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
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
SAXS Beam Line: What
WAXS
detector
slits: h & v
SAXS detector
up to 5m flight path
mono:
multilayers
& Si(111)
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
-
•
•
•
•
•
focusing
mirror (h & v)
bend magnet
between
beamlines
4 and 5
Specifications:
Focused flux ~ 1e12 hn/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
SAXS Beam Line: Where
Bending magnet
satisfies most
requirements; flux
frequently not
limiting factor
• unused bending
magnet
• enough space for
long hutch
between beam lines 4 (present) & 5
SAXS Beam Line: What & How Much
WAXS
detector
mono:
multilayers
& Si(111)
SAXS detector
up to 5m flight path
Estimated Cost
Front end & optics:
Hutch (slits, detector):
Sample environments:
Total:
slits: h & v
$3.0M
$0.7M
$0.3M
$4.0M
focusing
mirror (h & v)
bend magnet
between
beamlines
4 and 5
Sample environments:
- furnace to ≈800o C
- multi-sample holder (≈12) up to 200o C
- chamber for windowless SAXS
- grazing incidence-SAXS chamber
SAXS: Fuel Cell Catalysts
Fuel Cells: Efficient conversion of
chemical energy into electrical energy
Membrane-Electrode Assembly
(PEM Fuel Cells)
Goals:
 reduce cost: reduce Pt catalyst
loading from present ~0.5mg/cm2
 improve durability
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
C42 C50 ETEK Pt edge Particle Size Distribution
1.80
SAXS: Pt-M Alloy Catalysts
1.60
1.40
1.20
Probability
Determine nanoparticle size
distribution & changes during
operation in Pt-alloys
4-2 with Strasser, Leisch, Koh, Fu
After corrosion
1.00
0.80
Before testing
0.60
0.40
0.20
0.00
0
2
4
6
8
10
12
Particle Diameter / nm
Pt edge L_C42
Particle Size
Pt edge C42
Pt edge L_C50
Pt edge C50
Pt edge L_ETEK
Pt edge ETEK
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)
In-Situ SAXS
Electrochemical Cell
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?
Electrically Active Materials: Catalysts,
medical implants, energy conversion
devices, electronics
Do better designs exist for a more robust
material set?
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)
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 redoxactive 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 Line
Science:
• nanoparticles: metal alloy (fuel
cells), oxides, minerals
• polymers: fibrels, co-polymers
• supramolecular assemblies
• metallic glasses
• nanoporous materials
• colloids
• particles on surfaces/films
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)
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.
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.
1.
2.
3.
4.
5.
6.
7.
8.
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
SAXS: Basics
Q = k’ - k
|Q| = (4p/l)sin q
scattered
k’
Q
incident k
2q
• Measure I(Q) with Q  0.0001 – 1 Å-1
• Scattering from 1-100 nm density inhomogeneities
SAXS: Basics
Isolated particles
or pores with
diameter D
Hexagonal packed
cylinders
p/D
Q-4
• Need large Q range:
1/D <
~Q<
~ 10/D
Nanoporous Films: SAXS
Find:
Huang et al, Appl. Phys. Lett. 81, 2232 (2002)
• reasonably small pores (good)
• board distribution of pore sizes
(bad)
• size increases with loading =>
agglomeration (bad)