| First General Session | THE NANOSCIENCE REVOLUTION |
Merging of Colloid Science, Catalysis and Nanoelectronics
Gabor A. Somorjai,
Department of Chemistry and Lawrence Berkeley National Laboratory
University of California, Berkeley, CA 94720-1460, USA
Monodispersed platinum nanoparticles in the 1-8 nm range have been grown in solution capped by polymers using colloid science methods. These particles have been assembled in 2-dimensions using a Langmuir-Blodgett technique or in 3-dimensions using a mezoporous oxide support (SiO2, Al2O3). After removal of the organic coating multipath catalytic reactions are carried out to probe reaction selectivities as a function of metal particle shape, size and oxide-metal interface.
Photolitographic techniques were developed [Size Reduction Litography (SRL)] to fabricate nanowire and nanodot molds of silicon. These were pressed into a polymer to produce platinum nanowires and nanodots using imprint lithography. Catalytic reaction and reaction poisoning studies revealed that the oxide-metal interface sites resist deactivation.
Exothermic catalytic reactions at the metal surface produce a flux of hot electrons that can reach the oxide-metal interface if the metal particle size is smaller than the electron mean free path. By using a semiconductor (TiO2 or GaN) a Schottky diode (Pt/TiO2 or Pt/GaN) was fabricated and a continuous flow of electrons could be detected at the electrode on the semiconductor side. The flow of electrons should influence chemistry at the oxide-metal interfaces.
References
1. Catalysis and Nanoscience, Jeff Grunes, Ji Zhu and Gabor A. Somorjai. Chem.Commun.Focus Article, 2257 (2003).
2. The Catalytic Nanodiode. Gas Phase Catalytic Reaction Generated Electron Flow Using Nanoscale Platinum Titanium-Oxide Schottky Diodes, X. Z. Ji, A. Zuppero, J. M. Gidwani, and Gabor A. Somorjai. Nano Letters 5, 753 (2005).
3. High-Surface Area Catalyst Design: Synthesis, Characterization, and Reaction Studies of Platinum Nanoparticles in Mesoporous SBA-15 Silica, R. M. Rioux, H. Song, J. D. Hoefelmeyer, P. Yang, G. A. Somorjai. J. Phys. Chem. B 109, 2192 (2005).
4. Sum Frequency Generation Vibrational Spectroscopy Characterization of Surface Monolayers: Catalytic Reaction Intermediates and Polymer Surfaces, G. A. Somorjai, K. C. Chou, and M. Yang e-Journal of Surface Science and Nanotechnology. 2, 106 (2004).
5. Sublithographic Nanofabrication Technology for Nanocatalysts and DNA Chips, Y.-K. Choi, J. S. Lee, J. Zhu, Gabor A. Somorjai, L. P. Lee and J. Bokor. J. Vac. Sci. Technol. B 21, 2951 (2003).
Semiconducting and piezoelectric Nanostructures of Functional Oxides - From materials chemistry to controlled growth and to novel devices
Zhong Lin (ZL) Wang
School of Materials Science and Engineering
Georgia Institute of Technology, Atlanta, GA 30332-0245, USA
Piezoelectricity is an important phenomenon that characterizes the electromechanically coupled response of a material, and it has widely been used in science and technology. At nano-scale, most of the studies have been carried out for exploring the semiconducting properties of quantum dots, nanowires as well as nanotubes, but the nano-scale piezoelectric property remains an unexplored field until recently [1-6]. In our laboratory, we have synthesized a series of novel nanostructures of ZnO, a material that is semiconducting and piezoelectric. The piezoelectric coefficient of a piezoelectric nanobelt has been found to be almost tripled compared to the value of the bulk [7], clearly indicating the exciting applications of piezoelectric ZnO nanobelts for nano-scale electromechanical coupled sensors, transducers, switches and resonators. The two important characteristics of the wurtzite structured ZnO are the non-central symmetry and the polar surfaces. The structure of ZnO can be described as a number of alternating planes composed of tetrahedrally coordinated O2- and Zn2+ ions, stacked alternatively along the c-axis. The oppositely charged ions produce positively charged (0001)-Zn and negatively charged (000-1)-O polar surfaces, resulting in a normal dipole moment and spontaneous polarization along the c-axis. The polar surface results in a few interesting growth features [3, 4, 6]. This presentation will focus on the growth mechanisms and potential applications of piezoelectric nanobelts, nanorings and nanosprings.
References
[1] Z.W. Pan, Z.R. Dai and Z.L. Wang, Science, 209 (2001) 1947.
[2] W. Hughes and Z.L. Wang, Appl. Phys. Letts., 82 (2003) 2886.
[3] X.Y. Kong and Z.L. Wang, Nano Letters, 2 (2003) 1625 + cover.
[4] Z.L. Wang, X.Y. Kong and J.M. Zuo, Phys. Rev. Letts. 91 (2003) 185502.
[5] "Nanowires and Nanobelts materials, properties and devices; Vol. I: Metal and Semiconductor Nanowires, Vol. II: Nanowires and Nanobelts of Functional Materials edited by Z.L. Wang, Kluwer Academic Publisher (2003).
[6] X.Y. Kong, Y. Ding, R.S. Yang, Z.L. Wang, Science, 303 (2004) 1348.
[7] M. Zhao, Z.L. Wang, S. X.Mao, Nano Letters, 4 (2004) 587.
[8] For details please visit http://www.nanoscience.gatech.edu/zlwang
Research supported by NSF, DARPA, NASA and ONR
Small is Different, Some Interesting Properties and Potential Applications of Metals Confined to the Nanometer Size Scale of Different Shapes
Mostafa A. El-Sayed
Laser Dynamics Lab
Georgia Institute of Technology
Atlanta, GA30332-0245, USA
Reducing the size of material to below the size scale required for their characteristic electronic motion (which is on the nanometer scale) changes their properties and makes them sensitive to further reduction in size or changing their shape.
In this talk, the origins of some of these new properties(1-3) will be discussed and the potential applications and limitations of these nanoparticles in shape dependent colloidal nanocatalysis(4), in cancer diagnostics(5) and photothermal therapy(6) and in photonics(7) will be discussed.
References
1. C., Burda; X., Chen; R., Narayanan; M.A., El-Sayed, The Chemistry and Properties of Nanocrystals of Different Shapes, Chem. Rev. 105(4), 1025-1102, (2005), Invited Review Article.
2. Mostafa A. El-Sayed, "Some Interesting Properties of Metals Confined in Time and Nanometer Space of Different Shapes", Acc. Chem. Research, 34, (4), 257-264 (2001).
3. Stephan Link, Mostafa A. El-Sayed, Optical Properties and Ultrafast Dynamics of Metallic Nanocrystals, Annual Review Phys. Chem., 54:331-66, (2003).
4. Radha Narayanan and Mostafa A. El-Sayed, Catalysis with Transition Metal Nanoparticles in Colloidal Solution: Nanoparticle Shape Dependence and Stability, J. Phys. Chem. B (invited Feature Article) (2005).
5. El-Sayed, Ivan; Huang, Xiaohua; El-Sayed, Mostafa A., Surface Plasmon Resonance Scattering and Absorption of anti-EGFR Antibody Conjugated Gold Nanoparticles in Cancer Diagnostics; Applications in Oral Cancer, Nano Letters, 4(5), 829-834, (2005).
6. El-Sayed, Ivan; Huang, Xiaohua; El-Sayed, Mostafa A., Selective Laser Photo-Thermal Therapy of Epithelial Carcinoma Using Anti-EGFR Antibody Conjugated Gold Nanoparticles, Cancer Letters, (2005) in press.
7. Wenyu Huang; Wei Qian; Mostafa A. El-Sayed, Coherent Vibrational Oscillation in Gold Prismatic Monolayer Periodic Nanoparticle Arrays, Nano Lett, 4, (9), 1741-1747, (2004).
