Si Substitution in Nanotubes and Graphene via Intermittent Vacancies

TL;DR

This study demonstrates a method to incorporate silicon impurities into graphene and nanotubes by combining vacancy formation with laser-activated adatom diffusion, enabling controlled doping for potential sensor applications.

Contribution

It introduces a novel approach using argon plasma and laser irradiation to achieve silicon substitution in carbon nanostructures, improving impurity control.

Findings

Silicon substitution densities of 0.15 nm$^{-2}$ in graphene and 0.05 nm$^{-2}$ in nanotubes.

Si incorporated in mono- and divacancies, with about two-thirds in mono-vacancies.

Method allows controlled impurity inclusion in 1D and 2D carbon lattices.

Abstract

The properties of single-walled carbon nanotubes (SWCNTs) and graphene can be modified by the presence of covalently bound impurities. Although this can be achieved by introducing chemical additives during synthesis, that often hinders growth and leads to limited crystallite size and quality. Here, through the simultaneous formation of vacancies with low-energy argon plasma and the thermal activation of adatom diffusion by laser irradiation, silicon impurities are incorporated into the lattice of both materials. After an exposure of $\sim$1 ion/nm$^{2}$, we find Si substitution densities of 0.15 nm$^{-2}$ in graphene and 0.05 nm$^{-2}$ in nanotubes, as revealed by atomically resolved scanning transmission electron microscopy. In good agreement with predictions of Ar irradiation effects in SWCNTs, we find Si incorporated in both mono- and divacancies, with $\sim$2/3 being of the first type. Controlled inclusion of impurities in the quasi-1D and 2D carbon lattices may prove useful for applications such as gas sensing, and a similar approach might also be used to substitute other elements with migration barriers lower than that of carbon.