Are Al2O3 and MgO tunnel barriers suitable for spin injection in graphene?

We report on the structural impact on graphene and multi-layers graphene of the growth by sputtering of tunnel barriers. Sputtered Al2O3 and MgO barriers were chosen for their well-known efficiency as spin injectors in spintronics devices. The impact of the growth on the structure of graphene and up to 4-layer flakes was analyzed by Raman spectroscopy. This study reveals that for Al2O3 growth, the impact is moderate for a monolayer and decreases sharply for bilayers and above. In the case of MgO all the flakes underwent a strong amorphization. Moreover, this reveals that while single layer graphene is believed to offer the best spin transport properties, the better robustness of multilayer graphene may ultimately make it a better choice for spintronics devices.