Optimal aspect ratio and excitation spectral region of individual Au_xAg_1-x alloy nanobars for plasmonic sensing

Besides aspect ratio AR and excitation wavelength lambda, material composition is also key parameter determining figure of merit (FOM) of individual AuxAg1-x (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8,1.0) alloy nanobars. In this paper, the corresponding x dependent refractive-index sensitivity factor (S) and FOM responses were numerically investigated as functions of AR and lambda by discrete dipole approximation. It demonstrates that S increases nonlinearly/linearly with lambda(LSPR)/AR for all x concerned while FOM achieves x dependent optimum at optimized lambda(LSPR) and AR. With x decreasing, S, FOM and optimal FOM are revealed to increase. The obtained S and FOM responses are analytically explained well by alloy dielectric response under dipolar LSPR condition. The surrounding medium effect on S and FOM response of optimized AuxAg1-x nanobar is discussed as well. The present work provides significant guideline for future Au/Ag based applications in plasmonic sensing and detection. (C) 2020 Elsevier B.V. All rights reserved.