Mechanically stacked 1 nm thick carbon nanosheets: Ultrathin layered materials with tunable optical, chemical and electrical properties

TL;DR

This paper reports a scalable method to produce multilayer carbon nanosheets with tunable properties, which transform into nanocrystalline graphene upon annealing, enabling ultrathin conductive coatings.

Contribution

A new scalable fabrication route for multilayer carbon nanosheets with tunable properties and their transformation into nanocrystalline graphene upon annealing.

Findings

Multilayer nanosheets up to five layers were successfully fabricated.

Optical, chemical, and electrical properties were characterized thoroughly.

Nanosheets transform into nanocrystalline graphene after annealing at high temperatures.

Abstract

Carbon nanosheets are mechanically stable free-standing two-dimensional materials with a thickness of ~1 nm and well defined physical and chemical properties. They are made by radiation induced cross-linking of aromatic self-assembled monolayers. Here we present a route to the scalable fabrication of multilayer nanosheets with tunable electrical, optical and chemical properties on insulating substrates. Stacks up to five nanosheets with sizes of ~1 cm^2 on oxidized silicon were studied. Their optical characteristics were investigated by visual inspection, optical microscopy, UV/Vis reflection spectroscopy and model calculations. Their chemical composition was studied by X-ray photoelectron spectroscopy. The multilayer samples were then annealed in ultra high vacuum at various temperatures up to 1100 K. A subsequent investigation by Raman, X-ray photoelectron and UV/Vis reflection spectroscopy as well as by electrical four-point probe measurements demonstrates that the layered nanosheets transform into nanocrystalline graphene. This structural and chemical transformation is accompanied by changes in the optical properties and electrical conductivity and opens up a new path for the fabrication of ultrathin functional conductive coatings.