Optical properties of aluminum silver alloy films deposited by magnetron sputtering

Highlights: ► Thin films of Al–10 wt.% Ag were deposited onto silicon substrates by DC magnetron sputtering. ► We studied the effect of annealing on the structure and optical properties of Ag–10 wt.% Al alloy films. ► VASE was employed to characterize the dielectric functions of the silver aluminum alloy films. ► Al–10 wt.% Ag alloy films with different annealing temperature is a material for plasmonics and metamaterials. - Abstract: Metallic alloys and intermetallics are potential candidates for plasmonic materials due to the large free electron densities. In this paper, optical properties and their annealing effects of Al–10 wt.% Ag alloy films prepared by direct current magnetron sputtering were investigated. The variable angle spectroscopic ellipsometry (VASE) was used to measure the dielectric function of the aluminum silver alloy films. We observe that the dissipative loss at optical frequencies of the deposited alloy films is reduced greatly by increasing the annealing temperature. The typical interband transition around 1.5 eV for the aluminum silver films is shifted to lower energy with the increase of annealing temperature. The surface topography of the alloy films was characterized using scanning probe microscopy (SPM) and high-resolution scanning electron microscopy (HR-SEM). X-ray diffraction (XRD) was performed to study the phase structure and grain size. A new δ phase Ag2Al is shown in the annealed alloy films with the temperature from 200 °C to 500 °C.