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(a) Two-probe gate-transfer characteristics measured from graphene transistors with various metal contacts. (b) Measured Dirac points plotted as a function of the work function of the metal electrode (averaged values from four to six devices). The inset of (b) shows an AFM image of a graphene field-effect transistor.
Position of the Dirac point in the gate response in relation to the work function of the metal electrode. The open squares represent the work functions of the metal surfaces (Ref. 21), and the solid triangles indicate the work functions of the metal-graphene complexes, as published previously (Ref. 14). The work function of the Ti-graphene complex, denoted by a solid star, was calculated using first-principles methods, as described in the text. The class of metals that physisorb onto the graphene surface are shown in (a) and those that chemisorb are represented in (b).
Geometries employed to calculate the work function of the Ti-graphene complex. (a) A metal nanoparticle adsorbed onto graphene. (b) A metal nanoparticle sandwiched between two graphene monolayers. (c) Four layers of Ti slab with graphene layers on both surfaces. The local potentials calculated along the arrows are plotted in the bottom panels. The energies in the vertical axes are with respect to the Fermi level.
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