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Systèmes nanoélectroniques hybrides : cartographies de la densité d'états locale

Abstract : Mesoscopic physic is currently dominated by transport measurements that extract overall electronic properties of the studied sytstems. Tunneling spectroscopy gives access to the local density of states (LDOS). Hence, we can probe the spatial evolution of the electronic properties especially at the interface between two materials with different properties. During this thesis, we built-up a scanning probe microscope at 100mK that combine both atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM helps to locate a single nanocircuit on insulating substrate thanks to a Length Extension Resonator (LER). We can then measure the tunneling spectroscopy on the conductive nanocircuit. The energy resolution of the system is of 70µeV. We show the experimental proof of such a system by measuring the proximity effect in copper island (normal island) connected by two superconducting leads in aluminum at equilibrium, out of equilibrium and with a magnetic field. We also measured the LDOS of graphene on Ir(111) that displays electronic properties close to the one of intrinsic graphene with p-doping of about 0.34eV. We observe spatial inhomogeneities of this doping forming charge puddles with a typical size af about 9nm. Those observations are close to previous results reported on graphene on SiO2. However, the profile of the measured puddles shows a strong correlation with the topography due to the modulation of the electrostatic potential induced by the metal below the graphene. A closer look to the DOS shows quasiparticles interferences forming DOS inhomogeneities. The typical size of the DOS structures is of the order of the Fermi wavelength with a linear dependence with energy as E=ħvFk with vF = 8.3±0.7x10^5m/s which is close to the theoretical Fermi velocity of 1x10^6m/s. This point out the presence intravalley scattering and demonstrate the fact that particles in graphene on Ir(111) are Dirac fermions without mass.
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Sylvain Martin. Systèmes nanoélectroniques hybrides : cartographies de la densité d'états locale. Autre [cond-mat.other]. Université de Grenoble, 2012. Français. ⟨NNT : 2012GRENY086⟩. ⟨tel-00833413⟩

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