Abstract
In this paper we evaluate the effect of oxidation on the total power scattered in the far field by a 60nm radius Al sphere in the presence of a substrate comprised of either Al or silica (SiO2). Using an effective medium approach to model the Al particle with an outer layer of alumina (Al2O3), we find that the UV peak of total energy scattered in the far field shifts towards longer wavelengths for volume fractions of Al2O3 up to 20%. When particles with these volume fractions are held above an Al substrate, enhancement of two orders of magnitudes of the far-field power radiated by a dipole in the gap can be observed. For larger volume fractions of Al2O3, the total intensity of light scattered is significantly reduced.
Highlights
In recent years a large number of papers in nanophotonics have been investigating the properties of aluminum because it is an abundant and low cost metal with plasmon modes in the visible and the ultraviolet [1,2,3,4,5,6,7,8]
Al nanostructures can significantly enhance the detection of fluorescence by emitters for which the emission rate is much less than the internal nonradiative decay rate [11] when the emitter is strongly coupled to electromagnetic modes that efficiently transport energy into the far field
Our investigation of effective media spheres held above an Al substrate indicates that two orders of magnitude enhancement of the far-field radiation in the UV will take place with oxidized Al particles as long as the volume fraction of Al is not below 80%
Summary
In recent years a large number of papers in nanophotonics have been investigating the properties of aluminum because it is an abundant and low cost metal with plasmon modes in the visible and the ultraviolet [1,2,3,4,5,6,7,8]. By changing the size of the nanoparticle, resonances can be tuned between 150 nm and 650 nm and enhance, by orders of magnitude, both the far-field radiation and the decay rates of dipolar emitters placed in the gap between the nanoparticle and the substrate. This could have a profound impact on sensing of many important molecules that have radiative decays in the ultraviolet much weaker than nonradiative decays. Examples of such molecules are alkanes [12], most amino acids [13] in proteins and peptides, and DNA bases
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