During this talk I will present some results recently obtained with multigate silicon transistors purposely designed for mesoscopic physics studies. For time reasons I will probably develop in details only one of the two following results (à la carte seminar!).
Atomic spectroscopy in the solid-state: a measurement of the valley-orbit splitting with two donors
The energy levels of a single donor in silicon are widely spaced due to the strong atomic-like electronic confinement. The ground state and first excited states produced by an arsenic donor atom are separated by the so-called valley-orbit splitting, which is significantly lower when the atom is in a nanowire (compared to when it is in bulk silicon) because it is sensitive to where the donor atom is positioned, nearby interfaces, and external fields. We fabricated a silicon nanowire with 2 phosphorus donors controlled by 3 voltage gates. In this compact device, the ground level of one donor atom acts as an energy filter that probes the levels of the other .
A hybrid metal/semiconductor electron pump for quantum metrology
 Electron pumps driven in the GHz frequency range are likely to trigger a new “quantum” definition for the ampere. We study single-island hybrid metal/semiconductor transistor pumps which combine the simplicity and efficiency of Coulomb blockade in metals with the unsurpassed efficiency of silicon switches. We achieve pumping of up to 7 electrons per cycle at 1GHz and find an even/odd effect in the current plateaus at zero bias which is well explained by multi-charge pumping with trajectories enclosing several Coulomb lines. Long term measurements with a cryogenic current comparator show a relative uncertainty of 3 parts per million. Furthermore our design includes a back gate which allows to control the impact of single background charges in the nanowire transistors on the stability diagram of the metallic island.
 B. Roche et al., PRL 108, 206812 (may 2012) “Detection of a Large Valley-Orbit Splitting in Silicon with Two-Donor Spectroscopy”
 X. Jehl et al., submitted to PRX (may 2012) “ A gigahertz hybrid metal/semiconductor electron pump with a few part-per-million relative uncertainty and offset charge control”