Deformations related to atom mixing in Si/SiO2/Si nanopillars under high-fluence broad-beam irradiation

Structures consisting of a single Si nanodot buried within an insulating nanometric ${\mathrm{SiO}}_{2}$ layer stacked between two Si layers show promising properties for room temperature operational single-electron transistors. Moreover, such structures are highly compatible with modern complementary metal-oxide semiconductor technologies. Metastable ${\mathrm{SiO}}_{\mathrm{x}}$ phase separates into a Si nanodot and insulating, homogeneous ${\mathrm{SiO}}_{2}$ during annealing, providing a solid path towards the desired structure. However, achieving the necessary amount of excessive Si, dissolved in the ${\mathrm{SiO}}_{2}$ for correct concentrations of ${\mathrm{SiO}}_{\mathrm{x}}$, remains a technological challenge. In this work, we investigate ion-induced atom mixing in pre-built $\mathrm{Si}/{\mathrm{SiO}}_{2}/\mathrm{Si}$ nanopillars, which is considered to be a technologically promising way to produce the necessary concentrations of spatially confined ${\mathrm{SiO}}_{\mathrm{x}}$ in a controlled manner. During the high-fluence ion irradiation, we notice a significant shortening of the nanopillar and preferential loss of O atoms. Both sputtering and nanoscale ion hammering are found to be the cause of the deformation. The ion-hammering effect on nanoscale is explained by multiple small displacements, strongly enhanced after the nanopillar was rendered completely amorphous. The methods presented here can be used to determine the ion-fluence threshold for sufficient atom mixing in spatially confined regions before the large structural deformations are formed.