Thermoelectric Properties of Stressed p-Doped Polycrystalline Hollow Nanotubes

Thermoelectric generators have the potential to efficiently convert waste heat into valuable electrical power. However, conventional thermoelectric materials face limitations in terms of efficiency, scarcity, high cost, and scalability, impeding their widespread adoption. Nanoengineering techniques have emerged as a promising solution to enhance the thermoelectric properties of abundant and inexpensive materials like silicon. Nevertheless, the integration of these nanostructures on a large scale, necessary for efficient waste heat recovery, remains a significant challenge.<br/>Recently, a novel class of nano-enhanced materials in the form of extensive, paper-like fabrics composed of nanotubes has been developed, offering a cost-effective and scalable approach to thermoelectric power generation [1]. However, the fundamental properties of the building blocks of these fabrics, namely the p-type silicon nanotubes, have not been individually investigated to date.<br/>This study conducts electrothermal measurements using microfabricated suspended nitride membranes to characterize the thermoelectric properties of these nanotubes, including the electrical and thermal conductivity as well as the Seebeck coefficient. Furthermore, Raman thermography is employed in order to accounting for the effects of thermal contact resistance in the thermal conductivity measurement. Raman spectroscopy is also used to examine the residual mechanical stress in the nanotubes and investigate its relationship with the observed thermoelectric properties. A network model is proposed to link the macroscopic thermal properties of the fabrics with those of the nanotubes. Additionally, the study investigates the light absorption within these hollow structures. Finally, the effects of SiGe alloy on the properties of the nanotubes are compared and discussed.<br/>By understanding the interplay between the morphology, structure, and thermoelectric properties of the nanotubes, a pathway can be established for the development of more mechanically stable and efficient fabrics, with the potential for commercializing waste heat recovery through this technology.<br/>[1] Morata et al. "Large-area and adaptable electrospun silicon-based thermoelectric nanomaterials with high energy conversion efficiencies" Nat. Comm. (2018), 4759, 9(1)