Ion shaping of single-layer Au nanoparticles in amorphous silicon dioxide, in silicon nitride, and at their interface

Abstract

We present the shape transformation of a single layer of Au nanoparticles (NPs) when embedded in, and at the interface of, amorphous $\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$ ($\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$) thin films upon irradiation with 185-MeV Au ions to fluences ranging from 0.3 to $30\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$. Transmission electron microscopy (TEM) and high angular annular dark field microscopy were used to study the ion-shaping process. The former allows us to follow the overall change in geometry, size, and structure, while the latter reveals information about the relative position with respect to the interface. For Au NPs embedded in a single material, a lower elongation rate for $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ was found in comparison to $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$. When at the interface of the two materials, TEM reveals a preferential elongation towards $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$. The latter demonstrates the use of $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ for confining the ion-shaping process within an intermediate $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$ layer. The simulation of the temperature evolution during a single-ion impact was used to understand the difference in elongation rates between $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$, as well as the asymmetric behavior when located at the interface using the three-dimensional inelastic thermal spike model with bulk thermophysical properties. The calculations show good agreement with the experimental observations and reveal a correlation between the thermal profile and the resulting NP geometry.