Abstract
Au and Ag nanoshells are of interest for a wide range of applications. The plasmon resonance of such nanoshells is the property of interest and can be tuned in a broad spectral regime, ranging from the ultraviolet to the mid-infrared. To date, a large number of manuscripts have been published on the optics of such nanoshells. Few of these, however, address the effect of particle size distribution and metal shell imperfections on the plasmon resonance. Both are inherent to the chemical synthesis of metal nanoshells and therefore to a large extent unavoidable. It is of vital importance to understand their effect on the plasmon resonance, since this determines the scope and limitations of the technology and may have a direct impact on the application of such particles. Here, we elucidate the effect of particle size distribution and imperfections in the metal shell on the plasmon resonance of Au and Ag nanoshells. The size of the polystyrene core and the thickness of the Au and Ag shells are systematically varied to study their influence on the plasmon resonance, and the results are compared to values obtained through optical simulations using extended Mie theory and finite element method. Discrepancies between theory and practice are studied in detail and discussed extensively. Quantitative information on the minimum thickness of the metal shell, which is required to realize a satisfactory plasmon resonance of a metal nanoshell, is provided for Au and Ag.
Highlights
Such polystyrene particles were used as dielectric cores for the synthesis of Au and Ag nanoshells (Scheme S1 and Table S1)
After centrifugation and washing to remove the excess of Sn2+ ions in solution, the aqueous dispersion of tin-modified polystyrene particles was added to an aqueous silver(I) diammine solution
The Ag seeding and subsequent plating were performed under inert gas atmosphere to prevent oxidation of Ag, since oxidation has a strong influence on the plasmon resonance [45]
Summary
Sub-micron-sized metal particles are of interest for a broad variety of applications ranging from chemical and biological sensing [1,2,3] to medical applications [4,5,6], photocatalysis [7,8,9,10], surface-enhanced Raman spectroscopy [10,11,12], sunlight harvesting [13,14,15], and light trapping [15,16,17,18] For all of these applications, their localized plasmon resonance is the property of interest, and the particles are used for plasmonic absorption and/or scattering. The plasmon resonance is dependent on the dielectric constant of the core [21] and shell material [22, 23], the diameter of the core, the thickness of the metal shell, and the refractive index of the surrounding medium [24,25,26]
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