Choosing Optical Constants for the Simulation of Ag, Au and Cu Nanospheres

The experimentally derived optical constants of metals are essential for the simulation of plasmonic structures, but there is a wide variation in the values given by different studies. We survey the available data and show that the choice of optical constants can lead to very large differences in the calculated optical properties of plasmonic nanoparticles. Optical constants can be tabulated as a complex refractive index, N= n+ik, and we have found that the values of k are generally in good agreement between studies, but values of n are given with large error margins and there is poor agreement between studies. In simulations of plasmonic nanoparticles, the peak position is related to k, and so is in fair or good agreement for most datasets. However, the optical cross section and the loss are related to n and can vary by up to a factor of three depending on the choice of optical constants. We identify the current optimum sources of optical constants for Ag, Au and Cu.