Optical constants and structural properties of thin gold films.

Dmitry I Yakubovsky,Valentyn S Volkov,Dmitry Yu Fedyanin,Yury V Stebunov,Aleksey V Arsenin

doi:10.1364/oe.25.025574

Abstract

We report a comprehensive experimental study of optical and electrical properties of thin polycrystalline gold films in a wide range of film thicknesses (from 20 to 200 nm). Our experimental results are supported by theoretical calculations based on the measured morphology of the fabricated gold films. We demonstrate that the dielectric function of the metal is determined by its structural morphology. Although the fabrication process can be absolutely the same for different films, the dielectric function can strongly depend on the film thickness. Our studies show that the imaginary part of the dielectric function of gold, which is responsible for optical losses, rapidly increases as the film thickness decreases for thicknesses below 80 nm. At the same time, we do not observe a noticeable dependence of optical constants on the film thickness for thicker samples. These findings establish design rules for thin-film plasmonic and nanophotonic devices.

Highlights

Nanoscale thin metal films are an inherent part of various nanophotonic and plasmonic applications [1,2], such as high-sensitive sensors [3], plasmonic circuits [4], nanolasers [5], optical metamaterials and metasurfaces [6,7], photonic hypercrystals [8], among others.investigation of the optical absorption of metal through interband and intraband electron transitions is an essential input for a comprehensive understanding of the correlation between the metallic films structure and plasmonic/nanophotonic device intrinsic characteristics
To summarize, thin films of polycrystalline gold of different thicknesses were grown by conventional e-beam evaporation technique on silicon substrates at room temperature
The proposed method utilizes an accurate estimation of the films thickness and the analysis of their morphology to enable the determination and reproducibility of the optical constants data

Summary

Introduction

Nanoscale thin metal films are an inherent part of various nanophotonic and plasmonic applications [1,2], such as high-sensitive sensors [3], plasmonic circuits [4], nanolasers [5], optical metamaterials and metasurfaces [6,7], photonic hypercrystals [8], among others.investigation of the optical absorption of metal through interband and intraband electron transitions is an essential input for a comprehensive understanding of the correlation between the metallic films structure and plasmonic/nanophotonic device intrinsic characteristics. Understanding of how the optical properties of metal films depend on thickness is important for improved theoretical studies, numerical modeling and overall optimized performance of plasmonic devices. In this context, it is important to note that a series of rules and recipes to aid researchers in depositing thick metallic films with structural and optical properties optimized for plasmonic applications has already been reported [12]. One should keep in mind that despite the abundance of materials which are in principle suitable for plasmonic applications (i.e., characterized by a significantly high real part ε ' of permittivity and a low imaginary part ε "

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