Formation, structure, and optical performance of AgCd/Ag₅Cd₈ phases in thin film form

Abstract

Thin films with approximate compositions of Ag₅₀Cd₅₀ and Ag₃₈Cd₆₂, corresponding to the intermediate phases AgCd and Ag₅Cd₈ found in the Ag–Cd intermetallic system, were deposited by two independent approaches—(1) co-evaporation of silver and cadmium and (2) deposition of consecutive very thin sublayers from the two metals (stacks) without further annealing. The alloying of the elements in the as-deposited thin films was studied by X-ray diffraction analysis. All samples contained a mixture of intermetallic Ag–Cd phases. The deposition method has a significant influence on both the phase formation and the structure of the as-deposited thin films. The co-evaporation method leads to formation of a wider variety of intermetallic compounds appearing as larger grains on the surface, while the alloying of Ag–Cd stacks reflects in much smaller dimensions of the grains, composed mainly by the phases corresponding to the composition of the thin films. The optical properties of the thin film coatings were characterized by UV–Vis–NIR spectrophotometry and spectroscopic ellipsometry. The dispersion of the complex permittivity, $\varepsilon^{*} = \varepsilon^{\prime} + j \cdot \varepsilon^{\prime\prime}$, was analyzed by the Drude–Lorentz model. The results show that the thin Ag–Cd films possess smaller values of the imaginary part of the complex permittivity than the thin silver films in the spectral region 4–6 eV. A maximum in the spectral range 6.2–8 eV of the loss function, $\mathrm{Im}\{-1/{\varepsilon }^{*}\}$ is observed. Based on these results the potential application of the intermetallic compounds AgCd and Ag₅Cd₈ as materials for UV plasmonics and photonics devices has been discussed.