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Nanoparticle Building Blocks for Functional Materials and Devices
Hao Zeng
Department of Physics, University at Buffalo-SUNY
50 nm
Summer School of Advanced Functional Materials 2006 Shenyang, China, July 6, 2006
MnFe2O4 Fe3O4, XFe2O4
FePt, CoPt, etc
S. Sun and C.B. Murray, JAP 85 4325 (1999). S. Sun, C.B. Murray, D. Weller, L. Folks and A. Moser, Science 287 1989 (2000). S. Sun and H. Zeng, JACS 124 8204 (2002).
Magnetic Properties
0.0015
0.04
0.0010
m (a.u.)
0.0005
m (a.u.)
0.00
0.0000
-0.0005
-0.04
-0.0010
Mr/Ms ~ 0.46 Hc ~ 590 Oe
-6000 -4000 -2000
0
2000 4000 6000
H (Oe)
-0.0015 -6000
600
700
(a) 10 nm Au, (b) 10 nm Au-incomplete Fe3O4 shell, (c) 10 nm Au-2nm Fe3O4 shell and (d) 10 nm Au-3 nm Fe3O4 shell Red-Shift of Au surface plasmon frequencies due to Fe3O4 shell
M.C. Escher, Drawing Hands (1948)
Nanoparticle Self-assembly
A drop of particle dispersion on solid substrate
Self-Organization
Solvent Evaporation
Solution concentration Temperature Amount of ligand Evaporation rate
22 nm 22 nm
Courtesy of Shouheng Sun
Crystal Orientation Control
B=[100] {400} {440}
B=[110]
Strong four-fold modulation of the ring intensity is due to the coherent alignment of the individual NPs’ spinel lattice with the cubic superlattice. Hao Zeng, Philip M. Rice, Shan X. Wang et al., J Am. Chem. Soc. 126 (37), 11458-11459 (2004).
L = Stabilizing Ligands: RCOOH, RNH2, R3P, polymers, ...Waals Van der
magnetostatic e.g.: oleic acid CH3(CH2)7CH=CH(CH2)7COOH
COO
+ ++ +- - - - -+ + -+ ++ -+ - - -++ +++
Applications of Nanoparticles
I. Advanced Magnets for
Computer Hard Drive
MRI
Magnetic levitation Train
And many, many more……
material requirements: High Ms, high Hc, high (BH)max nature limits: Ms vs. Hc
+ + - -++ - +-+ ++ -- --+ + + - - -+ +++
Magnetic ElectrostaticR Nanoparticles: Co, Fe (Fe2O3, Fe3O4), Ni, epulsion StericRepulsion FePt, FePd, CoPt, CoPd, CoFe
advantages: monodisperse, high yield, high crystallinity, tunability
Magnetic Nanoparticles synthesized by High Temperature Solution Phase Technique
Co Fe, Ni, etc
E. Shevchenko et al, Nature, 439, 55 (2006)
Multicomponent Heterostructures-Core-Shell
4 nm FePt/3 nm Fe3O4
H. Zeng, S. Sun, et al. Nano Lett., 4 (1), 187-190 (2004).
(1) Metal salt reduction
(2) Metal precursor decomposition
L L L L M L L L L
van der Waals Magnetic Dipoles Electric Dipoles
M
n+
+neL
Heat
e.g. Co2(CO)8
L
L L L L Co L L L L
-4000
-2000
0
2000
4000
6000
H (Oe)
PbSe nanorods and nanostars
Inside Front Cover: Anisotropic Growth of PbSe Nanocrystals on Au-Fe3O4 Hybrid Nanoparticles
ADVANCED MATERIALS 14 2006
Exchange Coupled Nanocomposite
Kneller, E. F., Hawig, R. IEEE Trans. Magn., 27, 3588 (1991). Skomski, R., Coey, J. M. D. Phys. Rev. B, 48, 15812 (1993).
spintronic devices Fe3O4 tunnel junction arrays nano-composites
hard-soft exchange-spring magnets
Chemical Routes to Magnetic Nanoparticles
high temperature (200-300 °C) organic solution phase synthesis
Binary Assembly
Redl et al, Nature, 423, 968 (2003). bring different materials together tunable properties, multi-functionality interaction between components leading to new physics
nanoparticle labels for bio-applications
Why Care About Nanoparticles
Quantum confinement: tunable band gap in quantum dots magnetic correlation lengths: different magnetization reversal mechanisms building blocks for functional materials and devices
(b) (a) (a) Fe3O4-Au-Fe3O4 (b) PbSe-Au-PbSe
Fe3O4 Fe3O4 (111)
(C)
4 nm
(d)
Localization and entanglement of electron wave functions can be tuned by dimensions of dots and wire
Spacing Control
COOH Co OOC Co OOC
ligand exchange
interparticle distance & Interparticle interactions determined by chain length
40 nm
20 nm
controlled annealing
data storage FePt Nanoparticle selfassembled arrays
biological applications bio-sensing targeted drug delivery hyperthermia MRI contrast enhancement high frequency magnetic material FeCo/ferrite core/shell
More Core-shells
Au-Fe3O4
