Silver Nanodisk: Synthesis, Characterization and Self-Assembly
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Silver Nanodisk: Synthesis, Characterization and Self-Assembly Sihai Chen, Zhiyong Fan and David L. Carroll Laboratory for Nanotechnology, School of Materials Science and Engineering, Clemson University, Clemson, SC 29634, U.S.A. Email: [email protected] ABSTRACT A new form of silver nanostructured materials, a silver nanodisk, is generated by a solutionphase approach. In this method, two main steps are applied: the first is the generation of the truncated triangular silver nanoplates, which are obtained by seed-mediated growth of silver particles using cetyltrimethylammonium bromide (CTAB) as the soft templates. The second is the mild aging of the above triangular silver nanoplate solution at 40 oC to get the desired silver nanodisks. Transmission electron microscopy and atomic force microscopy studies show that the nanodisk has a thickness of the order of 20 - 30 nm, and a diameter around 60 nm. X-ray and electron diffraction analysis reveal that the nanodisk is single crystal and with its basal plane as (111) lattice plane. These nanodisks display a strong surface plasmon absorption band at 475 nm; this band can be continuously tuned within 420 nm to 560 nm through adjusting the aging time. The formation of self-assembled monolayer of CTAB on the basal plane is suggested to account for both the anisotropic growth from triangular nanoplates to nanodisks, and the formation of large-scale necklace-like structures. INTRODUCTION Due to the strong surface plasmon resonant absorption band, silver nanoparticles have attracted wide attention. More interestingly, this surface plasmon band are shape sensitive. For example, Schultz et al [1] have shown that triangular particles can display the peak plasmon resonance wavelength mainly in the range of 600 – 700 nm while that of pentagons in the range of 500 – 560 nm. Mirkin et al [2] have also succeeded in the preparation of triangular nanoprisms which displayed a strong in-plane dipole plasmon resonance at 670 nm. These shape sensitive optical properties render silver hot materials for application in optics [1] surface enhanced Raman spectroscopy (SERS) [3], biological label and diagnosis [4]. Shaped silver nanostructures have been observed or synthesized using various chemical approaches. These include spherical particles [5] tetrahedral [6] cubic [7], triangular [8], pentagonal [1], hexagonal [9], decahedral [10], icosahedral, cuboctahedral [11], as well as nanorods and wires [12]. Also, dentritic nanostructures of silver have been generated [13]. Here, we wish to report a new kind of silver nanostructure, i.e., silver nanodisks, which are generated in large quantities using a solution-phase chemical approach. We found that the nanodisks display a strong surface plasmon band at around 475 nm. Furthermore, we can tune this band within 420 nm to 560 nm through a mild aging process. In addition, since the top surface of these nanodisks is covered with a self-assembled monolayer of long chain organic molecules, they provide an ideal model system that mimics the self-a
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