Combined spin filtering actions in hybrid magnetic junctions based on organic chains covalently attached to graphene.

We present a bias-controlled spin-filtering mechanism in spin-valves including a hybrid organic chain/graphene interface. Wet growth conditions of oligomeric molecular chains would usually lead, during standard CMOS-compatible fabrication processes, to the quenching of spintronics properties of metallic spin sources due to oxidation. We demonstrate by X-ray photoelectron spectroscopy that the use of a protective graphene layer fully preserves the metallic character of the ferromagnetic surface and thus its capability to deliver spin polarized currents. We focus here on a small aromatic chain of controllable lengths, formed by nitrobenzene monomers and derived from the commercial 4-nitrobenzene diazonium tetrafluoroborate, covalently attached to the graphene passivated spin sources thanks to electroreduction. A unique bias dependent switch of the spin signal is then observed in complete spin valve devices, from minority to majority spin carriers filtering. First-principles calculations are used to highlight the key role played by the spin-dependent hybridization of electronic states present at the different interfaces. Our work is a first step towards the exploration of spin transport using different functional molecular chains. It opens the perspective of atomic tailoring of magnetic junction devices towards spin and quantum transport control, thanks to the flexibility of ambient electrochemical surface functionalization processes.

Design and Analysis of a Ag Rhombus Nanoparticle Film-Coupled Plasmonic Nanostructure.

We design a coupled plasmonic nanostructure, which consists of a Ag rhombus nanoparticle positioned over a silver film, separated by a dielectric spacer layer, and perform numerical analysis by calculating the radiation loss resistance of this nanostructure as the perfect electric conductor metal based on the theory of transmission line modes. Compared with the nanocube or triangular nanodisk film-coupled plasmonic nanostructures introduced in the previous works, a stronger electric field enhancement was achieved in the Ag rhombus nanoparticle film-coupled nanostructure because of the fact that the sharp tip of the rhombus nanoparticle can generate field enhancement at a hot spot. In order to demonstrate that the sharp tip can confine the electromagnetic energies strongly, we also have calculated the Purcell factor and the far-field directivity of the quantum emitter in the vicinity of this nanostructure.