Tunneling spin injection on graphene is possible by using different materials as barriers1–3. However, the growth of ultra-thin tunnel barriers leads to the creation of pinholes, which in turn causes direct ohmic contact and a large suppression of spin polarization. This occurs due to a fundamental limitation known as the resistance mismatch problem4, which limits spin injection when the resistance of an injector contact, , is lower than the spin resistance of the graphene channel, . This is the result of contact-induced spin relaxation, which greatly decreases the measured spin signals5. In this work, we demonstrate an alternative approach to grow ultra-thin tunnel barrier contacts made by oxidizing aluminium on top of previously functionalized graphene. We show that molecular functionalization of graphene allows the growth of smooth, high quality tunnel barriers, leading to contacts with increased spin injection efficiency and enhanced spin signals by one order of magnitude. The functionalization process consists on the laser activated physisorbtion of benzoyl peroxide (BPO) molecules on graphene. This laser controlled photoreaction enables us to control both the spatial location and the degree of functionalization, as visualized by Raman spectroscopy maps via the intensity ratio of and peaks (ID/IG). We assess the quality of the oxide barriers using atomic force microscopy, charge transport and spin transport measurements. These results open the path towards engineering spintronic devices with spatially controlled functionalization and efficient tunnel contacts.References: Tombros, N. et al, Nature 448, 571–574 (2007). Tombros, N. et al, Phys. Rev. Lett. 101, 2–5 (2008). Han, W. et al, Phys. Rev. Lett. 105, 167202 (2010). Schmidt, G. et al, Phys. Rev. B 62, R4790–R4793 (2000). Maassen, T. et al, Phys. Rev. B 86, 235408 (2012).

Spin Injection Enhancement via ultra-thin Oxide barriers into Molecularly Functionalized Graphene

K3: Spin Injection and Transport in Nanoscale Devices

technical paper

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Jesús Toscano Figueroa

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Spin Injection Enhancement via ultra-thin Oxide barriers into Molecularly Functionalized Graphene