Size Effect Of Nanoparticles In Cermet Films

Due to their unique optical, electrical properties and potential applications based on quantum size effect, small size effect and interface effect, cermet films consisting of ceramic matrix and embedded metal nanoparticles are attracting increasing attention for both fundamental and practical reasons. In this paper, we research the effect of particles size on optical properties of cermet films that consist of MgF2 matrix and embedded noble metal nanoparticles. The paper can be divided into three parts. In the first part, the international achievement of cermet thin film study is reviewed, which includes the technology of preparing the thin films, microstructure analysis, and influence of the size, shape and distribution of metal particles on the optical and electrical properties of cermet films. Three effective medium theories (Maxwell-Garnett, Bruggeman and Ping Sheng theories) and their corresponding models are presented in the second part of the paper. In the last part, the optical constants of Cu-MgF2, Ag-MgF2 and Au-MgF2 cermet films with different noble metal volume fractions in the spectral range of 200-850 nm are quantitatively calculated according to Maxwell-Garnett, Bruggeman and Ping Sheng theories respectively. The effects resulting from the restriction of the mean free path of the conduction electrons by the size of the metal particles in the films are taken into consideration. We compare the theoretical results with the experimental results and discuss the applicability of the three effective medium theories to nanoparticles cermet films. As the position, intensity and width of the plasma resonance absorption peak are concerned, we find that Maxwell-Garnett and Ping Sheng theories are applicable for the cermet films with low metal volume fraction, while Bruggeman theory fits better than Maxwell-Garnett theory for Au-MgF2 films with high metal volume fraction. The results also indicate that by taking particle size effect into consideration, the theoretical values of optical constants of the cermet films are moreconsistent with experimental values. At last we discuss the discrepancy between thetheoretical results and the experimental results, and the factors that cause the discrepancy are analyzed as well.