Special Properties of Nanomaterials

1
Special Properties of Nanomaterials
High surface/bulk ratio

• Catalysis
• Nanoparticle reagents
• Heat dissipation
• Laminar flow

Finite size effects

• Quantum confinement
• Interparticle tunneling
• Proximity effects
• High probability of defect-
• free crystals

2
Semiconductor Core-Shell Quantum Dots

• Perfect quantum well structure leads to bright
  luminescence
• Nanocrystal size determines band gap

Emission spectra of several sizes of (CdSe)ZnS
core-shell quantum dots M. Bawendi, et al., J.
Phys. Chem. B 1999, 101, 9463.
3
2.1 - 4.6 nm
CdSe/CdS core-shell particles Excitons confined
to core
Defect-free nanocrystals high fluorescence
quantum yield
Dual fluorescence labeling of actin filaments and
fibroblasts
A. P. Alivisatos et al., Science 1998, 281, 2013.
4
Shape Control of Semiconductor Nanocrystals

• Nanocrystal habit controlled
• by surfactant composition
• Multiple injection/growth cycles
• develop specific crystal faces

Cd
Se
L. Manna, E. C. Scher, A. P. Alivisatos, JACS
122, 12700 (2000)
5
CdSe Tetrapods
L. Manna, E. C. Scher, A. P. Alivisatos, JACS
122, 12700 (2000)
6
Conducting Polymer - Nanocrystal Solar Cells
Two-color system - can utilize solar spectrum
efficiently High aspect ratio nanocrystals,
organized superstructure should minimize carrier
recombination
W. U. Huynh, J. J. Dittme, A. P. Alivisatos,
Science 295, 2425 (2002)
7
Vapor-liquid-solid (VLS) growth of semiconductor
nanocrystals
Single crystal nanowires Catalyst nanoparticle
controls diameter Length determined by reaction
time
Y. Wu, P. Yang, J. Am. Chem. Soc., 123, 3165,
2001
8
Compositionally Modulated Semiconductor
Nanocrystals
Totem pole and core-shell structures Multiple
bandgaps and p-n junctions
Lieber, et al., Nature 415, 617 (2002) Nature
420, 57 (2002). Yang, et al., NanoLett 2, 83
(2002) Buhro et al., J. Am. Chem. Soc. 123, 4502
(2001).