Optical properties of ultrathin aluminum films deposited by magnetron sputtering in visible band

A set of ultrathin aluminum films deposited by direct current (DC) magnetron sputtering were studied on optical properties in the visible band ex situ. The contaminated surface layer were studied on thickness by X-ray photoelectron spectroscopy (XPS), as well as its influence on reflectivity and transmittivity of these films by scanning spectrophotometer. The optical constant and permittivity were calculated from the measured reflectivity and transmittivity of these films. All results show that the optical properties depend on the film thickness. Comparison between the experimental results and the simulation based on Maxwell-Garnett model of effective medium theory (EMT) on permittivity indicates the essential underlying role of microstructure in the optical properties of the ultrathin aluminum films.