Graphene nanostructuring for energy conversion at nanoscale

The energy conversion involving thermoelectricity, that is the ability of certain materials of generating a difference of potential when a gradient of temperature is present, could be in principle a useful way of recovering the energy dissipated in form of heat in any device. The efficiency of the thermoelectric energy conversion is maximized in correspondence of high values of the thermoelectric figure of merit ZT. Together with the simple temperature to voltage conversion, good charge carriers transport and low phonon transport, resulting in high electrical conductivity and low thermal conductivity, are essential requirements to obtain an efficiency for practical applications. 2D materials are known to be good candidates for thermoelectric conversion due to their different- dimensionality density of states. However, graphene, which is the most commonly used 2D material, presents a very high thermal conductivity which limits the energy conversion. My internship work has been focused on the nanostructuring of a mesh of pores on multilayer graphene with the aim of increasing phonon scattering and, as a consequence, reducing the thermal conductivity. By doing so, it would be possible to exploit its outstanding electronic properties to obtain good thermoelectric energy conversion without the limitations given by the phonon transport. A final comparison between two similar devices, nanomeshed and non-nanomeshed, is presented. A low energy carrier filtering probably induced by the holes can be deduced, and a lowering of the thermal conductivities can be observed. Finally, these modifications allowed an improvement of the thermoelectric figure of merit ZT of a factor higher than 3.