Debye Lecture 8
Self-Assembled Nanocrystal Superlattices:
Preparation and Properties.
C. B. Murray
Designing Nanoscale Materials
Lecture Series by 2004 Debye Institute
Professor
Christopher B. Murray
IBM Research
Ornstein Laboratory 166
Office phone 253 2227
cbmurray@alum.mit.edu
Cobalt Nanocrystal Superlattices (T. Betley et al)
Hexagonal packing
Cubic packing
10 nm Cobalt NCs
3D Colloidal supercrystals of nanocrystals
Crystallisation at the liquid - liquid interface
leads to formation of perfectly facetted
colloidal crystals
Optical micrograph of CdSe
3D colloidal crystals
Adv. Mater. 2001, 13, 1868.
HRSEM image
Three-dimensional colloidal supercrystals
of CoPt3 nanocrystals
Institute of Physical Chemistry, University of Hamburg,
Hamburg, Germany
Modeling NP Shape
Modeling Stacking faults
Scattered Intensity (arbitrary units)
Equivalent Diameter ~63Å
Spherical
1:1
(b)
Prolate
1.22
(a)
10
20
30
40
2θ
50
60
Small angle X-ray Scattering SAXS
4
sin( qR ) − qR cos( qR ) 2
π R 3 [3
]]
3
( qR ) 3
Where ρ and ρo are the electron density of the particle and the dispersing medium respectively. Io is the incident intensity and N is the number of
particles. F(q) is the material form factor (the fourier transform of the shape of the scattering object) and is the origin of the oscillations observed.
Thus for a spherical particle of radius R
(4.8)
I ( q ) = I o N [( ρ − ρ o ) 2
(4.9)
I(q ) = I o N( ρ − ρ o ) 2 F 2 (q )
(4.10)
F( q ) =
4 3 sin(qR) − qR cos(qR )
πR [3
]
3
(qR ) 3
/\/\/\
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A
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P \
0=Se=P
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0=P
0=P \/\/\/\/
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0=P\
Cap exchange to modify surface:
/
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P
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=P /
Se
\/
\\/\
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\/\/\/ P
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/\/\/\/ 0
\
P=0
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/\/\/\ =Se
\
P
/
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\/\/\/\/ /
N
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Pyridine
o
∆ 60 C
N
C
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/ \
N
/
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N
∆
Py
ra
z
80 o ene
C
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//\/\/\/\/\/\/\/\/\/
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0=P
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F
N
N
N
N N
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=0
/\/\/\/\/\/\/\/\/\/ P=0
/\/\/\/\/\/\/\/\/\/
e
P= S
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\
/\/\ \/\/ /\/\/P
/\/\ \/\/ =0
/\/\ P=
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0
/\/\/\/\/\/\/\/\/\/ P=0
N
/
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/
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0=P /\/\/\
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Se=P
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0=P /\/\/\/\/\/\/\/\/\/
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=P/\/\
Se
\/\
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D
V ac uu m
∆ 15 0 o
C
N
Tricetylphosphate
o
∆ 80 C
\
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\
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NN
/\/\/\/\/\/\
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/
0
P=
0
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B
N
N
N
N
N
N
N
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=P/\ /
Se /\/\/
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P\/\/
0=Se=P
0=\P
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0=P \/\/\
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/
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\/\/\ P
=0
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P=0
/\/\/ e
=S
/\/\/ P
PO
/ TB N
T BP o
C N
N
∆ 60
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0=P\
N N N
N
/\/\/\/\/\/\/\/\/\/\/
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N
N N N
N
N
N
N N
N N
N N
N N
N N
N N
N
N
N
N N
N
N NN
N
N
N
N
N
E
N
\
(444)
(333)
(222)
(220) (311)
log intensity / a.u.
(111)
TEM image of a
superlattice formed by
nanocubes. Inset: Electron
diffraction pattern of a 3D
superlattice showing
directional ordering.
The superlattice shows
cubic symmetry.
λ=0.154 nm
0
2
4
6
8
2Θ / deg
10
Small angle X-ray (SAXS) reflections
for a fcc superlattice formed by spheres
log intensity / a.u.
TEM image of a 3D
superlattice formed
by nanospheres with
hexagonal symmetry.
Inset: Wide angle
electron diffraction
pattern indicates
directional ordering
(see arrow)
0
2
4
6
8
λ =0.179
nm10
2Θ / deg
SAXS of a superlattice formed by cubes
5 nm
100 nm
TEM micrographs of a fcc superlattice showing the (112) projection (left)
and the (100) projection (right)
25 nm
600 nm
TEM micrographs of a quantum cube superlattice
Quantum Dot Solids for Amplified Stimulated Emission
V. I. Klimov, A. A. Mikhailovsky, Su Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H.-J. Eisler,
M. G. Bawendi, Science, 290, 314 (2000).
Quantum Dot Solar Cells
90 wt% QDs
W. U. Huynh, J. J. Dittmer, A. P. Alivisatos, Science 295, 2425 (2002).
FePt Nanocrystals (4 nm)
A
60 nm
B
30 nm
C
D
80 nm
5 nm
Magnetic recording
Computer
V
Servo
Electronics
I
4 nm ferromagnetic
FePt particle assembly
Writing
>
Slider
Sample
> X-Y Piezo Scanning Stage
to piezos
Reading
500 fc/mm
4
2
0
1040 fc/mm
MR signal [mV]
-2
-4
-6
2140 fc/mm
-8
-1 0
5000 fc/mm
-1 2
-1 4
-1 6
-1 8
-2 0
0
5
10
15
x [µ m ]
20
25
Spin-dependent tunneling in Nanocrystal arrays
Chuck Black, Bob Sandstrom, Chris Murray, Shouheng Sun
I (pA)
400
T = 70 K
T=2K
200
0
-200
-400
-0.4
shortest current path ~ 8 nanocrystals
-0.2
0.0
V (V)
0.2
0.4
10
2
10
1
10
0
10
-1
10
-2
10
-3
1.00
20
40
60
80x10
-3
-1
1/T (K )
data fit by:
ln(GV=0) = const. - Ec/kBT
from fit to data, measure EC~ 10 meV
for all devices measured, 10 meV < EC < 14 meV
R/RH=0
GV=0 (1/GΩ)
GV=0 follows simple thermal-activation
H
H
0.98
0.96
0.94
0.92
-0.4
-0.2
0.0
0.2
applied field (T)
0.4
Magnetic Nanomaterials for Functional Nanodevices
Researchers: Shouheng Sun, Hao Zeng, Min Chen
Single component
Self-assembly
Self-assembled Fe3O4 NPs
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
20
15
H =0
H = 3.5 T
I (nA)
10
5
0
-5
-10
-15
-20
-4
-3
-2
-1
0
1
2
3
-0.4
4
-0.2
0.0
0.2
0.4
VB (V)
-0.26
-0.25
-0.28
-0.26
-0.27
-0.30
MR
MR
-0.28
-0.32
-0.29
60 K
-0.34
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Vb
-0.30
100 K
-0.31
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
Vb
Potential for spintronic device applications
Qunatum cubes:
Cubic 12 nm PbSe nanocrystals Assembling into a superlattice.
(100) (112)
(111) (101)
Large terrace on PbSe Superlattice of 10 nm PbSe Nanocrystals
Self-assembled CdSe nanorod solids
without
polarizers
with
crossed
polarizers
20 µm
20 µm
Optical micrograph of self-assembled CdSe
nanorods (between crossed polarizers).
Figure 8: a) TEM image of a single cubic superlattice built of cubic FeO nanocrystals with 11 nm edge length. b) TEM image of a
larger superlattice oxidized or decomposed after storage. c) SAED of the cubic superlattice in b) showing reflections for magnetite
and orientational ordering in the superlattice.
Figure 4: a) LRTEM image of a quadratic subunit of a TEM grid showing nearly cubic superlattice built up of cubic wuestite
nanocrystals. b) SAED of a selected superlattice with uneven but symmetric intensity distribution caused by preferred alignment of the
particles (orientational ordering). c) TEM image of aligned superlattices arising during deposition of cubic FeO nanocrystals in a
magnetic field parallel to the substrate. d) TEM image of aggregated superlattices deposited without external magnetic field.
Fe3O4 nanoparticles
Sun et al, J. Am. Chem. Soc. 2004, 126, 273.
Shape induce crystal alignment
(14 nm MnFe2O4 nanoparticles)
(100) texture
(400)
16000
14000
Y Axis Title
12000
10000
8000
6000
4000
2000
(220) (311)
20
30
40
(511) (440)
50
60
70
80
2θ
(100) texture
H. Zeng, et al