# 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.

## Key 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$_2$.