Atomic packing: microstructure? • Cluster shape? • Surface ...
Transcript of Atomic packing: microstructure? • Cluster shape? • Surface ...
![Page 1: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/1.jpg)
Atomic Scale Ordering in Metallic NanoparticlesAtomic Scale Ordering in Metallic Nanoparticles
Structure:
• Atomic packing: microstructure?
• Cluster shape?
• Surface structure?
• Disorder?
![Page 2: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/2.jpg)
CharacterizationCharacterization
• Electron Microscopy• Scanning Transmission Electron Microscopy (STEM)• Electron Diffraction
• X-ray Absorption Spectroscopy• X-ray Absorption Near Edge Spectroscopy (XANES)
• Provides information on chemical states– Oxidation state– Density of states
• Extended X-ray Absorption Fine Structure (EXAFS)• Provides local (~10 Å) structural parameters
– Nearest Neighbors (coordination numbers)– Bond distances– Disorder
![Page 3: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/3.jpg)
(111)
(001)
(110)
Face Centered Cubic StructureFace Centered Cubic Structure
![Page 4: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/4.jpg)
Electron MicrodiffractionElectron Microdiffraction
[011] [112]
[310]
Electron diffraction probes the ordered microstructure of the nanoparticles. Above are 3 sample diffraction patterns for ~ 20 Å Pt nanoparticles. All are indexed as face-centered cubic (fcc).
![Page 5: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/5.jpg)
XX--Ray Absorption SpectroscopyRay Absorption Spectroscopy• Absorption coefficient (µ) vs. incident photon energy
• The photoelectric absorption decreases with increasing energy
• “Jumps” correspond to excitation of core electrons
Adapted from Teo, B. K. EXAFS: Basic Principles and Data Analysis; Springer-Verlag: New York, 1986.
Abs
orpt
ion
Photon Energy
![Page 6: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/6.jpg)
Extended XExtended X--ray Absorption Fine ray Absorption Fine StructureStructure
• oscillation of the X-ray absorption coefficient near and edge
• local (<10 Å) structure surrounding the absorbing atom
Photon Energy (eV)
11400 11600 11800 12000 12200 12400
Abs
orpt
ion
( µx)
0
1
EXAFS
Pt foil
µxII
= ln 0
I0 IT
x
Pt L3 edge (11564 eV)
![Page 7: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/7.jpg)
• Excitation of a photoelectron with
wavenumber k = 2π/λ
hν
initial final
e-
E0
PE = hν - E0
Ri
• Oscillations, χi(k): final state interference
between outgoing and backscattered photoelectron
)2sin()()( iii kRkAk =χ
Ri - distance to shell-iAi(k) - backscattering amp.
Basics of EXAFSBasics of EXAFS
![Page 8: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/8.jpg)
Abs
orpt
ion
( µx)
0
1
Photoelectron Energy (eV)
0 200 400 600 800
µµ0µ0(0)
k2 χ(k)
(Å-2
)
0 2 4 6 8 10 12 14 16-3
-2
-1
0
1
2
3
k (Å-1)
)0()(
0
0
µµµχ −=k
Convert to wave number
Subtract background and normalize
Data AnalysisData Analysis
Resulting data is the sum of scattering from all shells
∑=i
i kk )()( χχ
)(202 Ehmk −= ν
h
![Page 9: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/9.jpg)
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
| χ(r
)|(Å-3
)
r (Å)
R2
R3R4
Pt L3 edge, Pt foilR
1
Fourier TransformFourier Transform
Resolve the scattering from each distance (Ri) into r-space
![Page 10: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/10.jpg)
MultipleMultiple--Shell FitShell Fit
Calculate Fi(k) and δi(k) for each shell-i (i = 1 to 6) using the FEFF computer code
))(2sin()()(222
2 kkRekR
kFNk iik
i
iii δχ σ += −
Non-linear least-square refinement: vary Ni, Ri, σ2i using the EXAFS equation
0 1 2 3 4 5 6 7 8 9 100
1
2
3Pt L3, Pt foil
Multiple-Shell Fit Bond distance, Ri (Å)
R1 R2 R3 R4 R5
fit 2.768(3) 3.914(4) 4.794(4) 5.535(5) 6.189(6)
actual 2.7719 3.9200 4.8010 5.5437 6.1981
![Page 11: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/11.jpg)
SS2
SS3
SS4
SS5
DSTS
TR3
TR2
TR1
SS1
Multiple Scattering PathsMultiple Scattering Paths
In-plane atom
Above-plane atom
Absorbing atom
![Page 12: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/12.jpg)
11560 11565 11570 11575 11580 11585 11590 11595 116000.0
0.2
0.4
0.6
0.8
1.0
1.2
Nor
mal
ized
abs
orpt
ion
coef
ficie
nt
Energy, eV
XX--Ray Absorption Near Edge Spectroscopy (XANES)Ray Absorption Near Edge Spectroscopy (XANES)
XANES measurements for reduced 10%, 40% Pt/C, 60% Pt/C Pt/C, and Pt foil at 200, 300, 473 and 673 K. A total of 16 measurements are shown. All overlay well with bulk Pt (Pt foil); therefore, the samples are reduced to their metallic state.
![Page 13: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/13.jpg)
Size DependenceSize Dependence
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
Pt foil 60% Pt/C 40% Pt/C 10% Pt/C
FT M
agni
tude
, Å-3
r, Å0 2 4 6 8 10 12 14 16 18 20 22
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5 Pt foil 60% Pt/C 40% Pt/C 10% Pt/C
k2 χ (k)
, Å-2
k, Å-1
Size dependence on the extended x-ray absorption spectra. The amplitude of the EXAFS signal is directly proportional to the coordination numbers for eachshell; therefore, as the cluster size increases, the amplitude also will increase.
![Page 14: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/14.jpg)
i 10% Pt/C 40% Pt/C 60% Pt/C Pt foil Bulk fcc1 8.3(5) 10.5(5) 11.4(6) 12.6(7) 122 2.3(1.1) 4.0(1.3) 4.7(1.7) 5.9(2.0) 63 10.9(3.2) 16.8(3.5) 19(4) 23(5) 244 5.5(1.4) 7.6(1.4) 8.5(1.6) 11(2) 125 5.4(3.4) 10(4) 11(4) 14(5) 24
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
Data Fit
FT M
agni
tude
, Å-3
r, Å0 1 2 3 4 5 6 7 8 9 10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Data Fit
FT M
agni
tude
, Å-3
r, Å
Multiple Shell Fitting AnalysisMultiple Shell Fitting Analysis
10% Pt/C 40% Pt/C
![Page 15: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/15.jpg)
0 2 4 6 8 10 12 14 16 18 20 22-1.5
-1.0
-0.5
0.0
0.5
1.0
k2 χ(k)
, Å-2
k, Å-1
200 K 300 K 473 K 673 K
0 1 2 3 4 5 6 7 8 9 100.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
200 K 300 K 473 K 673 K
FT M
agni
tude
, Å-3
r, Å
Temperature DependenceTemperature Dependence
Temperature dependence on the extended x-ray absorption spectra for 10% Pt/C. As the temperature increases, the dynamic disorder (σD
2) increases, causing the amplitude to decrease.
![Page 16: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/16.jpg)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
Data Fit
FT M
agni
tude
, Å-3
r, Å0 1 2 3 4 5 6 7 8 9 10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Data Fit
FT M
agni
tude
, Å-3
r, Å
0 1 2 3 4 5 6 7 8 9 100.0
0.2
0.4
0.6
0.8
1.0
Data Fit
FT M
agni
tude
, Å-3
r, Å0 1 2 3 4 5 6 7 8 9 10
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Data Fit
FT M
agni
tude
, Å-3
r, Å
First Shell Fitting:First Shell Fitting: 10% Pt/C10% Pt/C
200 K 300 K
473 K 673 K
![Page 17: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/17.jpg)
Size Dependent Scaling of Bond Length and DisorderSize Dependent Scaling of Bond Length and Disorder
))(2sin()()(222
2 kkRekR
kFNk iik
i
iii δχ σ += −
200 300 400 500 600 700
2.7482.7502.7522.7542.7562.7582.7602.7622.7642.7662.7682.7702.7722.7742.7762.7782.7802.7822.7842.786
Dis
tanc
e, Å
Temperature, K
10% Pt/C 40% Pt/C 60% Pt/C Pt foil
( ) 2222dsrr σσσ +=−=
)/exp(1)/exp(1
2 E
E2TT
d Θ−−Θ−+=
ωµσ h
The EXAFS Disorder, σ2, is the sum of the static, σs
2, and dynamic, σd2,
disorder as follows:
The dynamic disorder, σd2, can be
separated by using the following relationship:
![Page 18: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/18.jpg)
Hemispherical cuboctahedron, (111) basal plane
Hemispherical cuboctahedron, (001) basal plane
Spherical cuboctahedron
Structure and MorphologyStructure and Morphology
• Determining shape and texture
• Electron microscopy
• X-Ray absorption spectroscopy
• Molecular modeling
![Page 19: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/19.jpg)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
2
4
6
8
10
12
14
16
18
20
22
24Bulk 3NN and 5NN
Bulk 2NN
Bulk 1NN and 4NN
Coo
rdin
atio
n nu
mbe
r
L
1NN 2NN 3NN 4NN 5NN
0 10 20 30 40 50 60 70 80
Cluster diameter, Å
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
2
4
6
8
10
12
14
16
18
20
22
24
Bulk 2NN
Bulk 1NN and 4NN
Bulk 3NN and 5NN
1NN 2NN 3NN 4NN 5NN
Coo
rdin
atio
n nu
mbe
r
L
0 10 20 30 40 50 60 70 80
Cluster diameter, Å
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
2
4
6
8
10
12
14
16
18
20
22
24
No overlap between 1NN and 2NN
1NN 2NN 3NN 4NN 5NN
Coo
rdin
atio
n nu
mbe
r
L
0 10 20 30 40 50 60 70 80
Bulk 2NN
Bulk 1NN and 4NN
Bulk 3NN and 5NN
Cluster diameter, Å
Theoretical Theoretical vsvs. Experimental. Experimental
Spherical
Hemispherical
![Page 20: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/20.jpg)
Molecular Modeling: Molecular Modeling: Understanding DisorderUnderstanding Disorder
• Probe bulk vs. surface relaxation.• Bulk:
Allow relaxation of entire structure.
• Surface:Allow relaxation of atoms bound in surface sites only.
![Page 21: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/21.jpg)
2.64 2.66 2.68 2.70 2.72 2.74 2.76 2.78 2.80 2.820
10
20
30
40
50
60
70
Freq
uenc
y di
strib
utio
n
1NN distance, Å
Surface Relaxation
• Theoretical:<d1NN> = 2.74 Åσ2 = 0.0022 Å2
• Experimental:<d1NN> = 2.753(4) Å σ2 = 0.0017(2) Å2
2.67 2.68 2.69 2.70 2.71 2.72 2.73 2.74 2.75 2.760
10
20
30
40
50
60
70
Freq
uenc
y di
strib
utio
n
1NN distance, Å
• Theoretical:<d1NN> = 2.706 Åσ2 = 0.0003 Å2
• Experimental:<d1NN> = 2.753(4) Åσ2 = 0.0017(2) Å2
Bulk Relaxation
Bond Length Distributions: Bond Length Distributions: 10% Pt/C10% Pt/C
<d1NN>BULK = 2.77 Å<d1NN>FOIL = 2.761(2) Å
![Page 22: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/22.jpg)
Bond Length Distributions:Bond Length Distributions: 40% Pt/C40% Pt/C
• Theoretical:<d1NN> = 2.689 Åσ2 = 0.0002 Å2
• Experimental:<d1NN> = 2.761(7) Åσ2 = 0.0010(2) Å2
Bulk Relaxation
2.68 2.70 2.72 2.74 2.760
50
100
150
200
250
300
350
400
Freq
uenc
y di
strib
utio
n
1NN distance, Å
Surface Relaxation
• Theoretical:<d1NN> = 2.76 Åσ2 = 0.0013 Å2
• Experimental:<d1NN> = 2.761(7) Åσ2 = 0.0010(2) Å2
2.66 2.68 2.70 2.72 2.74 2.76 2.78 2.80 2.820
500
1000
1500
2000
2500
3000
Freq
uenc
y di
strib
utio
n
1NN distance, Å
<d1NN>BULK = 2.77 Å<d1NN>FOIL = 2.761(2) Å
![Page 23: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/23.jpg)
Future DirectionsFuture Directions
• In-depth modeling of relaxation phenomena.
• Further understanding the “nano-phase” behavior of bimetallic particles.
• Polymer matrices as supports and stabilizers for nanoparticles.• Silanes• Hydrogels
![Page 24: Atomic packing: microstructure? • Cluster shape? • Surface ...](https://reader030.fdocuments.in/reader030/viewer/2022012711/61aae2e86dab6677a923a865/html5/thumbnails/24.jpg)
AcknowledgmentsAcknowledgments
Dr. Ralph Nuzzo
Dr. Andy GewirthDr. Tom RauchfussDr. John Shapley
Dr. Anatoly FrenkelDr. Michael Nashner
Dr. Ray TwestenDr. Rick Haasch
Nuzzo Research Group
Funding:Department of Energy
Office of Naval Research