Surface nanostructures forming during the early stages of the metal-assisted chemical etching of silicon. Optical properties of silver nanoparticles

In this two-part work, nanostructures formed in a three-step process of metal-assisted chemical etching of silicon are investigated. In the first part (present publication), the process of the chemical deposition of a layer of self-assembled silver nanoparticles on the surface of a silicon wafer (the first stage of metalassisted chemical etching) is studied. This layer, on the one hand, serves as a catalyst for the subsequent etching of silicon, and, on the other hand, represents a kind of mask for the formation of a certain topology of the emerging Si nanowires. The morphology of the obtained 40- to 60-nm-thick silver nanoparticle layers is investigated by scanning electron microscopy. The spectral dependences of the ellipsometric angles $\Psi$ and $\Delta$ are measured using spectroscopic ellipsometry ($\lambda$ = 250–900nm), and the complex dielectric function of the silver nanolayers is determined from these spectra. The dielectric function features a characteristic plasmon resonance peak in the ultraviolet spectral range. The study of the optical properties of Si nanofilament layers which form during the early stages of metal-assisted chemical etching will be reported as the second part of this work in a separate publication.