This paper presents modelled results for optical absorption in ultra-thin films of nickel, gold and silver across the solar spectrum. It is found that in the case of nickel there is an optimum thickness for maximum solar absorption around 10-13 nm. This is a result of the real and imaginary parts of its refractive index being of similar magnitude across the solar spectrum which gives rise to very strong thin film absorption.
This paper introduces the novel concept of a cross dipole nanoantenna for use in fluorescence based sensing applications. The dual-arm nature of the cross nanoantenna allows a dual resonant structure to be designed such that the shorter arm resonates with the pump wavelength and the longer arm with the emission wavelength. This is expected to further enhance emission from any fluorescent molecule that can couple to both nanoantenna arms when compared with a singly resonant structure. The paper uses the finite-difference time-domain method to first analyze the two-arm nanoantenna case and then shows how intensity enhancement depends on the antenna geometry and tapering of arms in the antenna gap. The results show that smaller gap sizes always produce larger enhancement compared with lightning rod effects due to tapering. A four-arm cross nanoantenna is then studied, highlighting differences from the two-arm case. Finally, the effect of a diagonally aligned molecule transiting the central gap region is studied. The results show that two hotspots occur on either side of the central gap region when the molecule is aligned perpendicular to the transit direction and only a single central hotspot occurs when the alignment is parallel to the transit direction.
This paper presents results obtained from finite difference time domain and transfer matrix method modelling of nickel thin films. It is shown that by adding a periodic 1D grating to the surface of the nickel its optical absorption over the 300 nm–1000 nm spectral range can be dramatically increased. 2D gratings show excellent polarization independence making them ideally suited to high temperature solar thermal applications.
General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Abstract: This paper presents measured fluorescence results for PMMA-dye coated 5 x 5 gold plasmonic nanoantenna arrays. The paper uses numerical electromagnetic modelling to show how array size and element spacing can be used to control emitted beamshape and compares this with experimental data. The Friis formula from RF antenna theory is used to calculate the intensity enhancement produced by the array. A figure-of-merit is then developed which accounts for the very small mode volume from which the array emission is occurring.
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