Electronic and Magnetic Properties of Quasifreestanding Graphene on Ni A. Varykhalov, 1 J. Sa ´nchez-Barriga, 1 A. M. Shikin, 2 C. Biswas, 1 E. Vescovo, 3 A. Rybkin, 2 D. Marchenko, 2 and O. Rader 1 1 BESSY, Albert-Einstein-Str. 15, D-12489 Berlin, Germany 2 V. A. Fock Institute of Physics, St. Petersburg State University, 198504, St. Petersburg, Russia 3 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973-5000, USA (Received 15 March 2008; published 10 October 2008) For the purpose of recovering the intriguing electronic properties of freestanding graphene at a solid surface, graphene self-organized on a Au monolayer on Ni(111) is prepared and characterized by scanning tunneling microscopy. Angle-resolved photoemission reveals a gapless linear -band dispersion near  K as a fingerprint of strictly monolayer graphene and a Dirac crossing energy equal to the Fermi energy (E F ) within 25 meV meaning charge neutrality. Spin resolution shows a Rashba effect on the  states with a large ( 13 meV) spin-orbit splitting up to E F which is independent of k. DOI: 10.1103/PhysRevLett.101.157601 PACS numbers: 73.20.At, 71.70.Ej, 79.60.Dp, 81.05.Uw Since its successful isolation by exfoliation from graph- ite samples [1], graphene has been among the most prom- ising materials for future electronic devices. In fact, there are separate developments in the realms of electronic trans- port and magnetoelectronics where this material excels: A remarkable conductivity with room-temperature mobilities of up to 1:5  10 4 cm 2 =Vs was observed and a half- integer quantum Hall effect indicates the presence of rela- tivistic charge carriers with vanishing mass [2–4]. It has been shown that the behavior of these massless Dirac fer- mions satisfies the laws of quantum electrodynamics, and the high mobilities may provide the basis for an extremely fast graphene-based electronics [2,5]. Alkali adsorption experiments have demonstrated the effect an external elec- tric field would exercise on electronic structure and band gap [6], and this prediction was confirmed by transport measurements of a graphene bilayer [7] thus presenting a key ingredient for an efficient graphene-based transistor. An acceleration of electronic devices is further expected from spintronics, where signal transmission is not achieved via transport of charge but spin. Graphene is being as- signed a role in spintronics since spin current manipulation was demonstrated in carbon nanotubes [8] and the realiza- tion of a spin valve was reported based on graphene [9]. The freestanding graphene sheet bridging permalloy and Au contacts leads to a 10% change in room-temperature resistance when the permalloy magnetization is reversed. This has been interpreted as successful spin injection into and efficient spin transport by the graphene [9]. With an extra oxide tunneling barrier between graphene and the ferromagnet, a large spin relaxation length of 1:5–2:0 m was obtained [10]. Recent photoemission investigations of a graphene monolayer on SiC indicate that the quasiparticle picture used to describe electron correlation in graphite [11] re- mains valid for the Dirac fermions in graphene and that photoemission investigations are therefore particularly valuable for assessing the electronic properties and pos- sible applications of graphene [12]. These investigations as well as the applications would benefit from a more practical and reliable method than mechanical exfoliation [1] to prepare continuous graphene sheets. One way to produce ultrathin graphite layers is the controlled evaporation of Si from heated SiC [13,14]. Transport properties have been investigated in 3-mono- layer-thick (ML) graphite films grown in this way which furthermore allows for lithographical patterning and con- ductance modulation by a gate electrode [15]. The relativ- istic charge carriers observed for freestanding graphene were observed in graphitized SiC as well [15]. It is, how- ever, difficult to control the thickness when graphitizing SiC by Si evaporation, and it is known that the half-integer quantum Hall effect disappears already for a freestanding film of two graphene layers [2]. Band structure measure- ments by photoemission were at first performed on films thicker than one monolayer [6,16], and truly monolayer graphene was achieved on SiC only most recently [12]. We pursue a very different way of producing a single graphene layer and decoupling it from its substrate. The method involves graphitization of Ni followed by interca- lation of Au [17]. While it has been established experi- mentally [17] and theoretically [18] that electronic binding energies in graphene on bare Ni differ largely ( 2 eV) from those in bulk graphite, successive Au intercalation, i.e., introduction of Au atoms into the interface between graphene and Ni, saturates the Ni3d bonds and weakens the chemical interaction between the graphene adlayer and its substrate as confirmed by phonon spectra [19]. This results in a shift of electronic  and  states towards lower binding energies [17]. In the present Letter, we investigate the electronic struc- ture of the graphene monolayer on Ni(111) intercalated with Au by angle-resolved photoemission in the vicinity of the Fermi energy (E F ). Its is demonstrated that this prepa- ration which employs self-organization takes the system closer to ideal freestanding graphene than any other prepa- ration on a solid substrate before, in particular, we will reveal seven key properties of our system: (i) The  band PRL 101, 157601 (2008) PHYSICAL REVIEW LETTERS week ending 10 OCTOBER 2008 0031-9007= 08=101(15)=157601(4) 157601-1 Ó 2008 The American Physical Society