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Adapting electronics to perfectly conform to non-planar and rough surfaces, such as human skin, is a very challenging task which, if solved, could open up new applications in fields of high economic and scientific interest ranging from health to robotics, wearable electronics, human machine interface and Internet of Things. The key to success lies in defining a technology that can lead to the fabrication of ultra-thin devices while exploiting materials that are ultimately thin, with high mechanical flexibility and excellent electrical properties. Here, we report a hybrid approach for the definition of high-performance, ultra-thin and conformable electronic devices and circuits, based on the integration of ultimately thin semiconducting transition metal dichalcogenides (TMDC), i.e., MoS2, with organic gate dielectric material, i.e., polyvinyl formal (PVF) combined with the ink-jet printing of conductive PEDOT:PSS ink for electrodes definition. Through this cost-effective, fully bottom-up and solution-based approach, transistors and simple digital and analogue circuits are fabricated by a sequential stacking of ultrathin (nanometer) layers on a few micron thick polyimide substrate, which guarantees the high flexibility mandatory for the targeted applications.

The low thermal conductivity of silicon nanostructures, with respect to bulk silicon, opens excellent possibilities for thermoelectric applications because it will enable the use of silicon for the high efficient direct conversion of wasted heat into electrical power. This paves the way for the application of silicon devices for energy scavenging and green energy harvesting. We present a device with a large number of nanostructures suspended on a silicon substrate. Top-down techniques for device fabrication based on advanced lithography and anisotropic etching will be discussed. FEM simulations were also carried out to analyze the temperature trend through the nanostructures.

Nanostructured silicon is a promising material for thermoelectric conversion, because the thermal conductivity in silicon nanostructures can be strongly reduced with respect to that of bulk materials. We present thermal conductivity measurements, performed with the 3$\omega$ technique, of suspended monocrystalline silicon thin films (nanomembranes or nanoribbons) with smooth and rough surfaces. We find evidence for a significant effect of surface roughness on phonon propagation: the measured thermal conductivity for the rough structures is well below that predicted by theoretical models which take into account diffusive scattering on the nanostructure walls. Conversely, the electrical conductivity appears to be substantially unaffected by surface roughness: the measured resistance of smooth and rough nanostructures are comparable, if we take into account the geometrical factors. Nanomembranes are more easily integrable in large area devices with respect to nanowires and are mechanically stronger and able to handle much larger electrical currents (thus enabling the fabrication of thermoelectric devices that can supply higher power levels with respect to current existing solutions).