• 3Ω measurement
• focused ion beam
• nanowires
• phonon scattering
• silicon
• thermal conductivity

This thesis is inserted in thermoelectric studies, and its aim is to find an innovative way to reduce thermal conductivity in silicon nanostructured devices. Silicon is an interesting material because it is the second most abundant element in nature, bio-sustainable, low cost and its thermal and electrical properties are well known in both industrial and research environments. The main limitation of silicon is its high thermal conductivity, but according to previous studies the thermal conductivity is significantly reduced (from 150 W/mK to 2 W/mK) in silicon nanostructures. In this thesis silicon nanowires are fabricated following MEMS techniques, such as electron beam lithography, chemical etching and thermal evaporation. The process is developed on a silicon-on-insulator (soi) wafer. A significant thermal conductivity reduction has been measured in silicon nanowires whose diameter is modulated periodically along its length: Focused Ion Beam etching has been used for the fabrication of grooves on the surface of nanowires. The thermal conductivity drops from about 40 W/mK to less than 10 W/mK. The thesis faced several challenges. At first, all the nanofabrication steps have been implemented and accurately calibrated; then a measurement procedure, based on 3Ω technique, has been developed and applied to silicon nanowires exploiting a self-heating/self-measuring concept; at the end, data have been reduced also through FEM analysis, for the calculation of the thermal conductivity.