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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 defectfree crystals 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. 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. Shape Control of Semiconductor Nanocrystals • Nanocrystal habit controlled by surfactant composition Cd Se • Multiple injection/growth cycles develop specific crystal faces L. Manna, E. C. Scher, A. P. Alivisatos, JACS 122, 12700 (2000) 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) 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 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).