Science à HERMES

The graphene is nowadays one of the most promising materials for next generation electronic devices. The graphene is a carbon bidimensional single crystal (single layer). The stacking of single graphene layers forms the graphite. The graphene was discovered for the first time by Andre GEIM, from Department of Physics of Manchester University, jointly with Konstantin NOVOSELOV. They both were awarded the Nobel Prize in 2010. The graphene has attracted a much attention these last years from academic researchers as well as industrials.

In 2003, a collaboration and research agreement between the CNRS and the SOLEIL national synchrotron was drawn up. This also included ELETTRA, the Italian synchrotron based in Trieste. The purpose of this agreement is to establish a formal collaboration between French and Italian research groups in the field of x-ray microscopy, and X-PEEM microscopy in particular (X-ray Photo-Emitted Electron Microscopy). SOLEIL’s X-PEEM microscope was therefore able to be installed on the French branch of the Nanospectroscopy beamline at ELETTRA whilst waiting for the soft x-ray microscopy beamline to be built at SOLEIL, where it is due to be installed in late 2010.

Nanomagnetism and spintronics have been receiving an ever increasing attention over the past two decades.

Une étude multi-techniques (LEEM*, LEED**, STM***) réalisée par une collaboration entre les équipes du LPN-Marcoussis, du synchrotron SOLEIL et du SPCSI, a permis de caractériser une nouvelle méthode d'élaboration de couches de graphène. Les couches sont obtenues sur des films minces de SiC déposés sur des substrats de silicium standards pour la microélectronique. Cette convergence entre une nouvelle technologie graphène et la technologie silicium est un pas vers la réalisation de composants électroniques de haute performance.

The ferromagnetic hexagonal α-phase of MnAs has a phase transition to the non-ferromagnetic orthorhombic β-phase at 318 K. The nature of magnetism in this phase has been the subject of many experimental and theoretical studies. The most recent theoretical work predicts either an antiferromagnetic or paramagnetic state. We have addressed this problem also from the experimental side, using epitaxial MnAs layers on GaAs. MnAs layers on GaAs are highly strained, which broadens the phase transition over a range of about 30 K. In this range α- and β-phase coexist. This allows studying both phases by combining XMLD- and XMCD-PEEM to determine the magnetic state of the β-phase and its interrelation with the ferromagnetic α-phase.