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Highlights

Photoemission in solids : concepts and applications

Photoemission is a spectroscopic technique that allows to study the physicochemical properties of surfaces as well as their electronic properties, as it measures the band structure of materials.

This book introduces the main concepts of the photoemission technique : core level photoemission and valence band photoemission. It also presents a variety of recent developments on nowadays subjects. Two readings are possible. There is an elementary level based on a one-electron approach to understand qualitatively the interest of this spectroscopy. There is also a deeper level based on a many-electron approach allowing to study interactions in condensed matter physics.

This book has been conceived for a broad audience, from undergraduate students for the more elementary aspects to specialized researchers on the technique in the presentation of concepts and application examples.

Boutique EDP Sciences

Ballistic transport in graphene nanoribbons

Extreme miniaturization of electronic devices is closely related to heat dissipation problems. Heat dissipation can be significantly reduced by changing from silicon to carbon electronics, as it was known from the studies on carbon nanotubes that showed ballistic (i.e. lossless) transport there. Devices on carbon nanotubes are feasible although it is difficult to place nanotubes at will. Graphene is an easily patternable material, but the ballistic transport had to be demonstrated, because most of the graphene ribbons exhibited a transport gap, incompatible with ballistic transport. Sidewall graphene nanoribbons do not have a transport gap and have the ideal electronic structure of undoped graphene as we observed by tunnel spectroscopy and photoemission. The transport measurements performed at GeorgiaTech and at the University of Hannover demonstrate an exceptional ballistic transport up to 16 μm even at room temperature, making them promising for extreme device integration and for lossless interconnects.

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Exceptional ballistic transport in epitaxial graphene nanoribbons. J. Baringhaus, M. Ruan, F. Edler, A. Tejeda, M. Sicot, A. Taleb Ibrahimi, Z. Jiang, E. Conrad, C. Berger, C. Tegenkamp, W. A. de Heer. Nature 506, 349 (2014).

Commented in Nature Physics News & Views 10, 182 (2014).

CNRS press release : http://www2.cnrs.fr/presse/communique/3419.htm.

Cover page of the CNRS annual report 2013.

Metal-insulator transition in Sn/Ge(111)

Upon deposition of 1/3 of atomic monolayer of Sn on Ge(111), a metallic reconstruction at room temperature. This reconstruction is sensitive to strong correlation effects, as its bands are rather narrow. The electrons at a same atom can no longer be considered as independent because of the electronic repulsion between electric charges of the same sign. The motion of electrons will be difficult due to this repulsion. The usual picture for describing the electronic properties of many materials (the band theory) is no longer valid. The band theory predicts these materials as metallic, while they are found to be insulating : they are called Mott insulators. We have observed the transition from a metallic phase to a Mott phase on Sn/Ge(111) below 30 K. Even if other surface systems had been interpreted previously as Mott insulators, we have observed the transition between the metallic and the insulating phases.

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Observation of a Mott insulating ground state for Sn/Ge(111) at low temperature R. Cortés, A. Tejeda, J. Lobo, C. Didiot, B. Kierren, D. Malterre, E.G. Michel, et A. Mascaraque. Physical Review Letters 96, 126103 (2006).
http://dx.doi.org/10.1103/PhysRevLett.96.126103

Commented in Nature News & Views 441, 295 (2006).