Coupling liquids with electronic excitations

The first seed for the begin of this internship, and the following PhD project, comes from previous works about a still mysterious water-carbon friction mechanism: it has been demostrated that water can interact directly with the carbon's electron, a quantum phenomena that has no precedent in fluid dynamics. On the base of this first observations, a quantum friction mediated current generation mechanism has been studied theoretically. The aim is to explore interfacial coupling processes between fluids and solids. This coupling arises from the coherent energy exchange between the collective modes of the fluid (which we coin ‘hydrons’) and the electronic and lattice excitations – plasmons and phonons –first with graphene, following previous experiments and then with confining semiconductors. The coupling between fluids and solids is opening a new area of investigations at the interface with semiconductor quantum devices that merges today at the same length scale. In this internship, I have started to investigate such peculiar dual system from two complementary perspectives. A first part is dedicated to study and characterization of the optical properties of thin highly doped semiconductor layers in the infrared spectral region, in particular the emergence of a collective effect coming from intersubband transitions. The coupling between this plasmon excitation and electromagnetic fields is intense, reaching the strong coupling regime without optical confinement. The radiative decay rate, Γ_rad(θ,ω), is a key parameter, indicating that under certain conditions, the radiative lifetime can exceed the nonradiative one, making radiative relaxation more favourable. Transmission FTIR measurements in different configurations and with different samples have been performed in order. A second part is dedicated to the discovery of the new Scanning Liquid Gate Microscopy. Scanning gate microscopy (SGM) is a standard technique that uses a conductive probe to locally modulate the electrostatic potential of a sample while simultaneously measuring its electrical response, leading to high resolution spatial maps of conductance. In this study we introduce a new variant of this technique, in which a local gate is realized through an electrolyte double layer (EDL) inside a micropipette manipulated by a macroscopic tuning fork (TF) AFM. Such liquid gating is used for its strong interfacial capacitance values, allowing to reach extremely high carrier density regime, compared to what can be achieved with standard solid gating. This allows us to develop a Scanning Liquid Gate Microscopy (SLGM), yielding a powerful, yet simple and non-invasive probing tool. We apply this new technique to graphene field effect transistors (GFET) in which the mean Fermi level can be easily tuned, and reveal charge puddles signatures. We highlight the exceptional simplicity and ease of use of out TF-AFM based SLGM. Finally, our preliminary results pave the way to systematic SGM investigations at ultra-high charge doping levels on graphene or semiconductors and could be used as a local probe of supercapacitance effects.