Graphene on insulating crystalline substrates

TL;DR

This paper demonstrates that ultra-thin graphene sheets can be prepared and identified on various crystalline substrates using standard techniques, with optical contrast and height measurements comparable to those on conventional substrates.

Contribution

It introduces a method to prepare and identify graphene on crystalline substrates and provides optical contrast calculations aligning with experimental data.

Findings

Graphene can be prepared on SrTiO3, TiO2, Al2O3, and CaF2 substrates.

Optical contrast of graphene on these substrates is between -1.5% and -8.8%.

Single-layer graphene height is approximately 0.34 nm on all tested substrates.

Abstract

We show that it is possible to prepare and identify ultra--thin sheets of graphene on crystalline substrates such as SrTiO$_3$, TiO$_2$, Al$_2$O$_3$ and CaF$_2$ by standard techniques (mechanical exfoliation, optical and atomic force microscopy). On the substrates under consideration we find a similar distribution of single, bi- and few layer graphene and graphite flakes as with conventional SiO$_2$ substrates. The optical contrast $C$ of a single graphene layer on any of those substrates is determined by calculating the optical properties of a two-dimensional metallic sheet on the surface of a dielectric, which yields values between $C=$ ~- 1.5% (G/TiO$_2$) and $C=$ ~- 8.8% (G/CaF$_2$). This contrast is in reasonable agreement with experimental data and is sufficient to make identification by an optical microscope possible. The graphene layers cover the crystalline substrate in a carpet-like mode and the height of single layer graphene on any of the crystalline substrates as determined by atomic force microscopy is $d_{SLG}=0.34$ nm and thus much smaller than on SiO$_2$.