The effects of the geometry parameters and oxidation on the localized surface plasmon resonance properties of copper nanoparticle thin film via calculation

Abstract Copper nanoparticles (CuNPs) possess localized surface plasmon resonance (LSPR) effect. Cu thin films composed of individual CuNPs present stronger LSPR effect than the individual CuNP due to the LSPR coupling among CuNPs. However, the LSPR of CuNPs in ambient conditions is rapidly damped due to oxidization. This has seriously hindered the applications based on the LSPR of CuNPs. Simulation of the variations of the coupled LSPR intensity and peak position of two adjacent CuNPs with the geometric parameters, ambient refractive index, and the thickness of oxide shell formed during oxidation is of great importance for understanding the mechanisms of the strong LSPR of CuNPs thin films and their rapid attenuation. In this paper, Discrete-dipole approximation method is used to simulate the extinction spectra of two adjacent spherical CuNPs as a function of ambient refractive index ( n ), the diameter ( D ) of the CuNPs, the inter-nanoparticle spacing ( L ) between two CuNPs, and the thickness ( t ) of the shell. The calculated results were compared with the experimental results. It is concluded that when the thickness of the oxide shell is small ( t/R < 0.5), increasing of n and decreasing of L/D of two adjacent CuNPs have an obvious synergistic effect which brings in the LSPR intensity enhanced and the peak redshift. But when the oxide shell thickness is large ( t/R > 0.5), the LSPR intensity is weakened and the peak shows blue shift. These results provide theoretical supports for rational selection and control of the parameters of CuNPs thin films and for various applications based on the LSPR of the CuNPs.