Self-Sustained Quasi-1D Silicon Nanostructures for Thermoelectric Applications

Abstract

Silicon (Si) nanowires have garnered significant interest for their potential applications in Si-based thermoelectrics, primarily due to their low thermal conductivity. While there are several methods to obtain Si nanowires, their density has been a limiting factor, resulting in a low power density that can be achieved by thermoelectric generators. To address this limitation, metal-assisted chemical etching (MACE) has been developed, enabling the creation of high-density nanopillar “forests”. This technique overcomes the previous density constraints. However, Si nanopillars protrude from a bulk Si wafer, which adds its thermal and electric resistivity to those of nanopillars, ultimately reducing the overall power density that can be attained. In this paper, we demonstrate how precise control of pre- and post-MACE processing allows for the creation of fully self-sustained quasi-1D Si nanostructures. We additionally demonstrate that pre-MACE Si processing does not control nanopillar bundling; rather, it primarily determines their shape. This outcome is attributed to the formation of gas nanobubbles during the initial steps of MACE.

Fabrication of Metal Contacts on Silicon Nanopillars: The Role of Surface Termination and Defectivity

“…This final step is critical since it implies that the final drying of the Si chip commonly occurs from an aqueous solution. Since the oxidizing agent causes the formation of a thin oxide layer on the Si NP surface, the final result is that the (flexible) NPs bundle up due to capillary forces [20,21], forming tip aggregates. Bundling may be avoided by replacing spontaneous drying with super-critical drying [22,23].…”

“…Bundling may be avoided by replacing spontaneous drying with super-critical drying [22,23]. As a simpler alternative, either water is replaced with less polar solvents or the NP surface oxide is etched by HF as a last step before drying [21], avoiding any capillary-driven tip agglomeration of nonpolar (hydrogenated) NP surfaces. In some cases, however, NP bundling may be desired and strengthened by willingly oxidizing NP surfaces (e.g., with H 2 O 2 ).…”