Atomic-Layer-Deposition-Made Very Thin Layer of Al₂O₃, Improves the Young’s Modulus of Graphene

Nanostructures with graphene make them highly promising for nanoelectronics, memristor devices, nanosensors and electrodes for energy storage. In some devices the mechanical properties of graphene are important. Therefore, nanoindentation has been used to measure the mechanical properties of polycrystalline graphene in a nanostructure containing metal oxide and graphene. In this study the graphene was transferred, prior to the deposition of the metal oxide overlayers, to the Si/SiO₂ substrate were SiO₂ thickness was 300 nm. The atomic layer deposition (ALD) process for making a very thin film of Al₂O₃ (thickness comparable with graphene) was applied to improve the elasticity of graphene. For the alumina film the Al(CH₃)₃ and H₂O were used as the precursors. According to the micro-Raman analysis, after the Al₂O₃ deposition process, the G-and 2D-bands of graphene slightly broadened but the overall quality did not change (D-band was mostly absent). The chosen process did not decrease the graphene quality and the improvement in elastic modulus is significant. In case the load was 10 mN, the Young’s modulus of Si/SiO₂/Graphene nanostructure was 96 GPa and after 5 ALD cycles of Al₂O₃ on graphene (Si/SiO₂/Graphene/Al₂O₃) it increased up to 125 GPa. Our work highlights the correlation between nanoindentation and defects appearance in graphene.