Böttcher et al. Nanoscale Research Letters 2011, 6:214 http://www.nanoscalereslett.com/content/6/1/214 N A N O E X P R E S S Open Access Graphene on ferromagnetic surfaces and its functionalization with water and ammonia Stefan Böttcher1,2, Martin Weser1, Yuriy S Dedkov1*, Karsten Horn1, Elena N Voloshina2*, Beate Paulus2 Abstract In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented. The results of adsorption on graphene/Ni(111) obtained in this study reveal the existence of interface states, originating from the strong hybridization of the graphene π and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach. Introduction Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with two crystallographically equiva- lent atoms (C1 and C2) in its primitive unit cell [1,2]. The sp2 hybridization between one 2s orbital and two 2p orbitals leads to a trigonal planar structure with a forma- tion of strong ∑ bonds between carbon atoms that are separated by 1.42 Å. These bands have a filled shell and, hence, form a deep valence band. The unaffected 2pz orbital, which is perpendicular to the planar structure of the graphene layer, can bind covalently with neighboring carbon atoms, leading to the formation of a π band. Since each 2pz orbital has one extra electron, the π band is half filled. The π and π* bands touch in a single point at the Fermi energy (EF) at the corner of the hexagonal graphene’s Brillouin zone, and close to this so-called Dirac point, the bands display a linear dispersion and form perfect Dirac cones. Thus, undoped graphene is a semimetal ("zero-gap semiconductor”). The linear disper- sion of the bands results in quasi-particles with zero mass, namely, the so-called Dirac fermions. The unique “zero-gap” electronic structure of gra- phene, however, leads to a few limitations for application of this material in real electronic devices. In order, for example, to prepare a practical transistor, one has to * Correspondence: dedkov@fhi-berlin.mpg.de; elena.voloshina@fu-berlin.de 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany. 2Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany. Full list of author information is available at the end of the article have a graphene layer where energy band gap is induced via application of electric field or via modification of its electronic structure by means of functionalization. There are several ways of the modification of the electronic structure of graphene with the aim of gap formation [3]. Among these ways are (i) incorporation within the struc- ture of nitrogen and/or boron or transition-metal atoms; (ii) use of different substrates that modify the electronic structure; (iii) intercalation of different materials under- neath graphene grown on different substrates; and (iv) deposition of atoms or molecules on top, etc. In this article, an attempt to modify the electronic struc- ture of graphene via contact of this material with metal (ferromagnetic Ni substrate) and via adsorption of polar molecules (H2O, NH3) on top of the graphene/metal sys- tem is presented. These studies of water and ammonia adsorption on graphene/Ni(111) were performed via com- bination of experimental [angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS)], and theoretical methods [density-functional theory (DFT) calculations]. XAS and ARPES studies of graphene/ Ni(111) reveal the existence of the interface states, origi- nating from the strong hybridization of the graphene π and Ni 3d valence band states with partial charge transfer of the spin-polarized electrons on the graphene π* unoc- cupied states. This leads to the appearance of induced magnetism in the carbon atoms of the graphene layer as confirmed by X-ray magnetic circular dischroism (XMCD). ARPES and XAS data of the H2O-NH3/gra- phene/Ni(111) systems enable us to discriminate between © 2011 Böttcher et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.