Effective method to study the thickness-dependent dielectric functions of nanometal thin film.

A new method for measuring the dielectric functions change with the thickness of nanometal thin films was proposed. To confirm the accuracy and reliability of the method, a nano-thin wedge-shaped gold (Au) film with continuously varied thicknesses was designed and prepared on K9 glass by direct-current-sputtering (DC-sputtering). The thicknesses and the dielectric functions in the wavelength range of 300-1100 nm of the nano-thin Au films were obtained by fitting the ellipsometric parameters with the Drude and critical points model. Results show that while the real part of the dielectric function (ϵ₁) changes marginally with increasing film thickness, the imaginary part (ϵ₂) decreases drastically with the film thickness, approaching a stable value when the film thickness increases up to about 42 nm. This method is particularly useful in the study of thickness-dependent optical properties of nano-thin film.