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 SiO2 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 SiOx phase separates into a Si nanodot and insulating, homogeneous SiO2 during annealing, providing a solid path towards the desired structure. However, achieving the necessary amount of excessive Si, dissolved in the SiO2 for correct concentrations of SiOx, remains a technological challenge. In this work, we investigate ion-induced atom mixing in pre-built Si/SiO2/Si nanopillars, which is considered to be a technologically promising way to produce the necessary concentrations of spatially confined SiOx 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.