# Spontaneous Intercalation of Graphene on Sapphire

## TL;DR

Graphene grown on sapphire improves its electronic performance over time due to spontaneous intercalation of oxygen-containing species at the interface.

## Contribution

Discovery of spontaneous intercalation of oxygen-containing species at the graphene-sapphire interface under ambient conditions.

## Key findings

- Spontaneous decoupling at the graphene-sapphire interface increases carrier mobility by twofold.
- Oxygen-containing species intercalate at the interface, reducing strain and doping in aged samples.
- XPS and TEM confirm intercalation as the mechanism for improved electronic performance.

## Abstract

The direct synthesis of graphene on dielectric substrates has attracted growing interest due to its potential for scalable, transfer‐free integration in electronic and photonic applications. However, graphene grown on dielectrics typically exhibits lower carrier mobility compared to copper‐grown counterparts, limiting its performance. Here, we report the synthesis of large‐area graphene on Al‐rich reconstructed c‐plane sapphire (0001) via chemical vapor deposition (CVD) and reveal that, over time and under ambient storage conditions, a spontaneous decoupling occurs at the graphene–sapphire interface. Raman spectroscopy reveals a reduction in both strain and doping in the aged samples, consistent with electrical transport measurements showing a twofold increase in carrier mobility. X‐ray photoelectron spectroscopy (XPS) and cross‐sectional transmission electron microscopy (cross‐sectional TEM) identify the intercalation of oxygen‐containing species at the interface as the mechanism responsible for the decoupling. These findings uncover a previously unrecognized pathway to enhance the electronic performance of directly grown graphene on sapphire, reinforcing the viability of this platform for future scalable graphene‐based technologies.

When left at room temperature, even in depressurized atmosphere, foreign molecular species can intercalate in between graphene and the (31
×
31)R9 reconstruction, effectively decoupling the graphene from its substrate: αAl2O3(0001). This is observed in the spectroscopic fingerprints, as well as in a large enhancement of the transport figures.