# Morphology modifcation of Si nanopillars under ion irradiation at elevated temperatures: plastic deformation and controlled thinning to 10 nm

## TL;DR

This study investigates how Si nanopillars change shape and can be thinned to 10 nm using ion irradiation at different temperatures, revealing the roles of amorphization, annealing, and sputtering.

## Contribution

It demonstrates controlled thinning of Si nanopillars to 10 nm by ion irradiation at elevated temperatures, combining experimental observations with 3D simulations.

## Key findings

- Nanopillars thinned to 10 nm at high temperature.
- Amorphization influences shape change at room temperature.
- Dynamic annealing prevents amorphization at elevated temperatures.

## Abstract

Si nanopillars of less than 50 nm diameter have been irradiated in a helium ion microscope with a focused Ne$^+$ beam. The morphological changes due to ion beam irradiation at room temperature and elevated temperatures have been studied with the transmission electron microscope. We found that the shape changes of the nanopillars depend on irradiation-induced amorphization and thermally driven dynamic annealing. While at room temperature, the nanopillars evolve to a conical shape due to ion-induced plastic deformation and viscous flow of amorphized Si, simultaneous dynamic annealing during the irradiation at elevated temperatures prevents amorphization which is necessary for the viscous flow. Above the critical temperature of ion-induced amorphization, a steady decrease of the diameter was observed as a result of the dominating forward sputtering process through the nanopillar sidewalls. Under these conditions the nanopillars can be thinned down to a diameter of 10 nm in a well-controlled manner. A deeper understanding of the pillar thinning process has been achieved by a comparison of experimental results with 3D computer simulations based on the binary collision approximation.