Dielectric function of sub-10 nanometer thick gold films

Abstract

A smooth gold (Au) film with thickness below 10 nanometer (nm) is hard to fabricate as well as to accurately measure its thickness and the corresponding dielectric function. Here, we report 5.4, 6.6 and 7.5 nm thick continuous Au films prepared on Chromium (Cr) seed layer. The thickness and dielectric function of the Au films are obtained using spectroscopic ellipsometry and first principles calculation. From the fitting results of the ellipsometric parameters, the value of the real part of dielectric function ($\varepsilon_{1}$) is negative almost in the whole spectrum region indicating that the Au films are continuous. For the imaginary part of dielectric function ($\varepsilon_{2}$), it decreases with increasing of the Au film thickness because the surface electrons scattering decreases. Moreover, the calculated and measured results of 5.4, 6.6 and 7.5 nm thick Au films present a good agreement in the wavelength range from 400 to 1600 nm. From the results of the first principles calculation, both $\varepsilon_{1}$ and $\varepsilon_{2}$ decrease with increasing of the Au film thickness. These precise measurement and calculation results of dielectric function are beneficial to nano-photoelectronic devices design with sub-10 nm Au films involved.