On the Structural and Chemical Characteristics of Co/Al(2)O(3)/graphene Interfaces for Graphene Spintronic Devices

We report a detailed investigation of the structural and chemical characteristics of thin evaporated Al(2)O(3) tunnel barriers of variable thickness grown onto single-layer graphene sheets. Advanced electron microscopy and spectrum-imaging techniques were used to investigate the Co/Al(2)O(3)/graphene/SiO(2) interfaces. Direct observation of pinhole contacts was achieved using FIB cross-sectional lamellas. Spatially resolved EDX spectrum profiles confirmed the presence of direct point contacts between the Co layer and the graphene. The high surface diffusion properties of graphene led to cluster-like Al(2)O(3) film growth, limiting the minimal possible thickness for complete barrier coverage onto graphene surfaces using standard Al evaporation methods. The results indicate a minimum thickness of nominally 3 nm Al(2)O(3), resulting in a 0.6 nm rms rough film with a maximum thickness reaching 5 nm.