Site-controlled formation of single Si nanocrystals in a buried SiO2 matrix using ion beam mixing

TL;DR

This paper presents a method for site-controlled fabrication of single silicon nanocrystals within a buried SiO2 matrix using ion beam mixing and thermal treatment, with detailed atomistic insights and precise control demonstrated.

Contribution

It introduces a novel ion beam mixing technique combined with focused ion beam patterning to achieve site-controlled single Si nanocrystals in a buried oxide layer.

Findings

Successful formation of single Si nanocrystals with 2.2 nm diameter.

Site-controlled assembly achieved using focused Ne+ ion beam.

Quantitative analysis of nanocrystal size and distribution based on experimental parameters.

Abstract

For future nanoelectronic devices - such as room-temperature single electron transistors - the site-controlled formation of single Si nanocrystals (NCs) is a crucial prerequisite. Here, we report an approach to fabricate single Si NCs via medium-energy Si+ or Ne+ ion beam mixing of Si into a buried SiO2 layer followed by thermally activated phase separation. Binary collision approximation and kinetic Monte Carlo methods are conducted to gain atomistic insight into the influence of relevant experimental parameters on the Si NC formation process. Energy-filtered transmission electron microscopy is performed to obtain quantitative values on the Si NC size and distribution in dependence of the layer stack geometry, ion fluence and thermal budget. Employing a focused Ne+ beam from a helium ion microscope, we demonstrate site-controlled self-assembly of single Si NCs. Line irradiation with a fluence of 3000 Ne+/nm2 and a line width of 4 nm leads to the formation of a chain of Si NCs, and a single NC with 2.2 nm diameter is subsequently isolated and visualized in a few nanometer thin lamella prepared by a focused ion beam (FIB). The Si NC is centered between the SiO2 layers and perpendicular to the incident Ne+ beam.