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

Emission spectra of several sizes of (CdSe)ZnS core-shell quantum dots

M. Bawendi, et al., J. Phys. Chem. B 1999, 101, 9463.

Semiconductor Core-Shell Quantum Dots

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

CdSe/CdS core-shell particles

Excitons confined to core

Defect-free nanocrystalshigh fluorescence quantum yield

A. P. Alivisatos et al., Science 1998, 281, 2013.

Dual fluorescence labeling of actin filaments and fibroblasts

2.1 - 4.6 nm

Cd

Se

Shape Control of Semiconductor Nanocrystals

L. Manna, E. C. Scher, A. P. Alivisatos, JACS 122, 12700 (2000)

• Nanocrystal habit controlled by surfactant composition

• Multiple injection/growth cycles develop specific crystal faces

CdSe Tetrapods

L. Manna, E. C. Scher, A. P. Alivisatos, JACS 122, 12700 (2000)

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)

Y. Wu, P. Yang, J. Am. Chem. Soc., 123, 3165, 2001

Vapor-liquid-solid (VLS) growth of semiconductor nanocrystals

Single crystal nanowiresCatalyst nanoparticle controls diameterLength determined by reaction time

Compositionally Modulated Semiconductor Nanocrystals

Totem pole and core-shell structuresMultiple 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).