Macroscopic Thermoelectric Legs Obtained by Encapuslating Forests of Self-Supporting Silicon Nanowires

The application of nanotechnology in the development of novel thermoelectric materials has yielded remarkable advancements in their efficiency. In many instances, dimensional constraints have resulted in a beneficial decoupling of thermal conductivity and power factor, leading to large increases in the achievable thermoelectric figure of merit (ZT). As a major example, single-crystalline silicon ZT increases by nearly two orders of magnitude when transitioning from bulk single crystals to nanowires. However, the practical implementation of nanostructured materials in thermoelectric devices remains somewhat restricted, not only due to manufacturing complexity and associated costs but also due to the limited power that nanomaterials deliver because of the reduced heat capture section [1]. Metal-assisted chemical etching offers a potential solution to overcome such limitations, enabling the production of dense, cost-effective forests of silicon nanopillars [2]. Nevertheless, use of pillared silicon chips in thermoelectric devices necessitates the non-trivial establishment of low-resistance electrical and thermal contacts atop the Si nanopillars. Furthermore, the residual single-crystalline silicon membrane adds thermal and electrical resistances that degrade the device performances. In this regard, we will present and compare strategies for achieving high-quality contacts through electroplating [3] and by embedding pillars into appropriate electrical and thermal insulators. Additionally, nanowire embedding will be shown to be of use also to encapsulate quasi-ordered millimeter-long nanowire aggregates, named 'nanofelts', that are obtained by fully etching thick silicon chips [4]. This provides a novel path to employ Si nanostructures with enhanced ZT to make thermoelectric legs with macroscopic sizes.<br/><br/>[1] Heremans, J. P.; Dresselhaus, M. S.; Bell, L. E.; Morelli, D. T.; Nat. Nanotechnol. 2013, 8 (7), 471–473.<br/>[2] Magagna, S.; Narducci, D.; Alfonso, C.; Dimaggio, E.; Pennelli, G.; Charaï, A.; Nanotechnology 2020, 31 (40), 404002.<br/>[3] Dimaggio, E.; Pennelli, G.; Nano Lett. 2016, 16 (7), 4348–4354.<br/>[4] Giulio, F.; Puccio, L.; Magagna, S.; Perego, A.; Mazzacua, A.; Narducci, D.; ACS Appl. Electron. Mater. 2023, accepted.