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Image potential states (IPSs) are electronic states localized in front of a surface in a potential well, formed by the surface projected bulk band gap on one side and the image potential barrier on the other. In the limit of a two-dimensional solid, a double Rydberg series of IPSs has been predicted, which is in contrast to a single series present in three-dimensional solids. Here, we confirm this prediction experimentally for mono- and bilayer graphene. The IPSs of epitaxial graphene on SiC are measured by scanning tunneling spectroscopy and the results are compared with ab-initio band structure calculations. Despite the presence of the substrate, both calculations and experimental measurements show that the first pair of the double series of IPSs survives and eventually evolves into a single series for graphite. Thus, IPSs provide an elegant quantum probe of the interfacial coupling in graphene systems.

International audience; We present an investigation of the atomic and electronic structure of graphene monolayer islands on the 6H-SiC(0001)(3×3) (SiC(3×3)) surface reconstruction using scanning tunneling microscopy (STM) and spectroscopy (STS). The orientation of the graphene lattice changes from one island to the other. In the STM images, this rotational disorder gives rise to various superlattices with periods in the nm range. We show that those superlattices are moir ́e patterns (MPs) and we correlate their apparent height with the stacking at the graphene/SiC(3×3) interface. The contrast of the MP in STM images corresponds to a small topographic modulation (by typically 0.2 ̊A) of the graphene layer. From STS measurements we find that the substrate surface presents a 1.5 eV wide bandgap encompassing the Fermi level. This substrate surface bandgap subsists below the graphene plane. The tunneling spectra are spatially homogeneous on the islands within the substrate surface gap, which shows that the MPs do not impact the low energy electronic structure of graphene. We conclude that the SiC(3 × 3) reconstruction efficiently passivates the substrate surface and that the properties of the graphene layer which grows on top of it should be similar to those of the ideal material.

International audience; The atomic and electronic structures of a graphene layer on top of the (2 × 2) reconstruction of the SiC (000 ̄1) surface are studied from ab initio calculations. At variance with the (0001) face, no C bufferlayer is found here. Si adatoms passivate the substrate surface so that the very first C layer presents a linear dispersion characteristic of graphene. A small graphene-substrate interaction remains in agreement with scanning tunneling experiments (F.Hiebel et al. Phys. Rev. B 78 153412 (2008)). The stacking geometry has little influence on the interaction which explains the rotational disorder observed on this face.

73.20.-r 68.55.-a; International audience; The early stages of the graphitization of the 6H-SiC(000N1) (3 3) surface in an Ultra-High Vacuum (UHV) are investigated by means of scanning tunneling microscopy (STM). Different kinds of graphitic islands are found on the surface. One kind (called G_3 3) consists of a single graphene-like carbon plane covering the initial (3 3) reconstructed substrate surface. We observe a broad distribution of rotation angles between the substrate and the carbon plane revealed by superstructures of different directions and periods. Low bias images show that the graphene structure is preserved close to the Fermi level. The data indicate a weak substrate-graphene coupling for the G_3 3 islands.

International audience; The early stage of graphene formation on the 6H-SiC 0001¯ surface is investigated by scanning tunneling microscopy. Islands made of a single graphitic plane form above regions of the substrate that show either a 2 2 C or a 3 3 reconstruction. The orientations of the single-layer domains present a broad distribution of rotation angles with respect to the substrate. The atomic structures of the 3 3 and 2 2 C substrate reconstructions are preserved under the first carbon layer. Low bias images reveal a graphitic structure, which indicates that the interaction between the first carbon plane and the SiC surface is comparatively much weaker on the C face than on the Si face of the substrate. The coupling is stronger on the 2 2 C surface reconstruction than on the 3 3 one, where an almost ideal graphene structure is found close to the Fermi level.

This work is devoted to an experimental study of metallic surfaces by scanning tunneling microscopy (STM). Some surfaces of noble metals and iron or nickel exhibit electronic states, localized near the surface, which may be either spin-splitted or non-magnetic and strongly or weakly dispersive. We take advantage of the spatial resolution of the STM to analyse the atomic structure of the surfaces as well as to locate and/or to create a unique nanoscale structure in order to study its electronic properties by tunneling conductance measurements. Eventually, this kind of nano-islands shows up electronic confinement that leads to quantum interferences detected by STM as electronic standing waves. First, the theoretical physical properties of the surface states (known as “Shockley Surface States”) are presented including a description of their scattering process with static surface defects. Then, we apply a method that seems to be the most efficient to perform local magnetic measurements and we present some preliminary results on the system made of a thin iron film on Ag(001). Another magnetic surface, Ni(111), is studied. Its electronic properties are characterized by analysing the quantum interference patterns associated to a nanoscale island of Ni on Ni(111) fabricated by indentation. The last part is dedicated to the deposition of Ni on Cu(111). This study is related to the chemical composition of the surface and mainly to the electronic properties of nanoscale nickel and copper structures. Finally, we discuss the effect of the chemical composition of these nanostructures on their electronic properties., Ce manuscrit présente une étude par microscopie à effet tunnel de surfaces de métaux de transition, dont les propriétés électroniques sont remarquables près du niveau de Fermi. Ces surfaces de métaux nobles, de nickel et de fer, possèdent des états électroniques localisés en surface, magnétiques ou non, fortement ou faiblement dispersifs. Pour ce travail nous avons utilisé la grande résolution spatiale du microscope pour analyser la structure atomique de surface, et également pour repérer et/ou créer des objets uniques nanométriques afin d'en étudier les propriétés électroniques par des mesures de conductance tunnel. Les nanostructures qui sont présentées ici sont souvent le siège d'un confinement électronique qui se traduit par la présence d'interférences quantiques observables sous forme d'ondes stationnaires électroniques par un microscope à effet tunnel. Dans un premier temps, nous présentons du point de vue théorique les propriétés physiques des états électroniques de surface dits de « Shockley » des métaux nobles et leur interaction avec les défauts statiques. Ensuite, nous exposons la méthode de mesure locale des propriétés magnétiques qui nous semble très performante et les résultats préliminaires que nous avons obtenus avec un système de film mince de Fe/Ag(001). La recherche d'échantillon magnétique présentant un état de surface nous a conduit à nous intéresser à un autre type de surface : Ni(111). Nous montrons comment nous pouvons nous servir des effets d'interférences quantiques observées dans des nanostructures de nickel créées par nano-indentation pour caractériser les propriétés électroniques de Ni(111). L'étude suivante concerne le dépôt de couches ultra-minces de Ni/Cu(111). Nous y étudions la chimie de la surface, des effets de diffusion d'atomes, et surtout les propriétés électroniques de nanostructures de nickel et de cuivre. Nous y discutons aussi de l'influence de la présence de Ni et Cu dans ces objets sur leurs propriétés électroniques.