| As one of the most important optical film materials currently available, magnesium fluoride (MgF2) possesses a low refractive index, low absorption, a high thermal stability and good transparency over a wide range of wavelengths. Recently, a lot of new hotspots have attracted researchers’attention, such as MgF2/metal multilayers, metal-intercalated MgF2photonic crystals, metal-MgF2nanoparticle cermet films, among which Ag/MgF2composite films is now an important concern because of their novel photoelectric properties. However, there are a lot of surfaces, interfaces and atomic interaction in Ag/MgF2composite films, which will have a significant effect on the microstructure and performances. So far, the research of Ag/MgF2about interface structure, interdiffusion behavior, and their effect on optical properties of remain to be further investigated. Due to the difficulties and limitations of experimental research, it is very important to simulate from atomic level. In recent years, exploration of the experimental mechanism and prediction of material’s properties from atomic level is becoming important means of materials science research. In this paper, interface of Ag/MgF2nanofilms were studied based on the first-principles. The main research results are as follows: (1) The structural stability, electronic properties, and optical properties of MgF2surfaces and nanofilms were analyzed. The structural stability of MgF2surfaces increases in the following order:(001),(100), and (110), which reveals the most close-packed surface, that is (110), is most stable. The surface energy of MgF2(100) nanofilms is smaller than that of (100) and (110) nanofilms and MgF2(100) nanofilms can exist stably. Further, MgF2(001) nanofilms are energetically stabilized when the layer number is increased to25, corresponding to a thickness of4nm. Refractive index of MgF2nanofilms is decreased compared with the bulk. With increasing thin film thickness, refractive index and their extinction coefficient of MgF2(001) nanofilms are decreased.(2) The structural stability, electronic and optical properties of Ag (111) surface and Ag (111) nanofilms were analyzed. Ag (111) nanofilms are energetically stabilized when the layer number is increased to13, corresponding to a thickness of2.8nm. Analysis on the optical properties of nanofilms suggests that refractive index is significantly increased and extinction coefficient is slightly decreased compared with the bulk in the visible light and infrared wavelengths. With increasing thin film thickness, the refractive index decreased slightly and the extinction coefficient increase.(3) The adsorption and diffusion of Ag on MgF2(100),(001) and (110) surfaces were studied. The results show that the adsorption is chemical and the energetically favorable adsorption sites of (100),(001), and (110) are hollow site, short bridge site and long bridge site, respectively. The structural stability of Ag-adsorbed surfaces increases in the following order:(100),(110) and (001). The interaction between Ag and Mg is ionic, while covalent between Ag and F. The diffusion of Ag at MgF2(001) surface is not easy. In the visible wavelength region, the refractive index of MgF2surface with Ag adsorption is slightly decreased compared with that of the bulk, while the optical absorption is slightly increased.(4) The interface characteristics of Ag/MgF2nanofilms were discussed. The most stable ideal interface structure of Ag (111)/MgF2(001) is obtained, which has the lowest interface energy. The analysis on the diffusion behavior shows that Mg diffuses into Ag film more easily, while Ag diffuses into MgF2film difficultly. Further, Ag diffusion results in a decrease in refractive index, especially in the visible light wavelength region. |
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