The structural and optical properties of amorphous silicon (a-Si) and Ag-dispersed amorphous silicon (a-Si:Ag) thin films irradiated by femtosecond (fs) laser at various energy densities are investigated comparatively in this article. It is found that at a lower energy density of 100 mg/cm<sup>2</sup> , the film microstructure evolves from a completely amorphous phase to an intermediate one containing both amorphous and polycrystalline silicon. During laser irradiation, the formation of nanocrystals in a-Si films begins at lower energy density, but the existing Ag nanoparticles inhibits somehow the crystallization of a-Si in a-Si:Ag films at the same energy density. As the energy density is increased to a moderate value of 200 mj/cm<sup>2</sup> , the surface of a-Si:Ag films featuring a vertically aligned pillar-shaped structure is emerging. Both the crystallinity and the root mean square of surface roughness exhibit a monotonic increase with the increase of energy density. The Ag nanoparticles are dispersed uniformly in a silicon matrix, resulting in a resonant light absorption due to so-called localized surface plasmon. The localized surface plasmon resonance (LSPR) wavelengthes of the irradiated aSi:Ag films are increased significantly from 600 nm to about 820 nm, and the bandwidth of the measured absorptance is enhanced in the range of 600~1600 nm. The nanocrystallization mechanism, the formation of pillar-shaped structures and the light absorption enhancement are explained regarding the high electron density and the plasma-surface interactions.
Much attention has been attracted by applications of memristor in data storage, unconventional computing and logic circuit since 2008, but very few have been focused on applications in optical switches and optical modulators. Here, by combining a silicon waveguide with a memristor of Ag/a-Si/p-Si structure, a novel optical switch (OS) for use at 1.55μm has been set up. The device consists of a bottom p-Si waveguide, an upper a-Si layer and a top Ag electrode, i.e. a sandwich structure named as Ag/a-Si/p-Si. The light transmitting through the silicon waveguide can be modulated by changing optical parameters of a-Si dielectric layer in which the formation and annihilation of Ag filament can be adjusted by an alternately electrical field between Ag and p-Si electrodes. The distribution of optical power dependence on the thicknesses of a-Si layer and Ag layer as well as the geometric size of waveguide have been studied by numerical analysis. Finally, based on Ag/a-Si/p-Si sandwich structure and the simulated results, we have proposed a new and improved OS.