Non-lithographic and scalable manufacturing of silicon micro & nanomaterials

In the last decade, accelerated discovery of novel processing schemes has enabled rapid prototyping and large volume production of parts with extended and programmable functionality - such as biodegradable electronics, high-emissivity surfaces, optoelectronics circuits, fast-discharging batteries, meta-materials, energy conversion systems, and light-weight composites. Novel micro/nanomanufacturing methods - such as 2D and 3D printing, imprinting, self-assembly, deterministic micro-assembly, flexography, and roll-to-roll systems - are among a growing set of new platforms that allow for integration of metals, polymers, oxides, composites, nanomaterials and biomaterials hierarchically across length scales ranging from centimeters down to nanometers. However, nanomanufacturing platforms are still plagued by a trade-off between throughput and resolution, ultimately hindering the scaling of nanomaterial production. In this context, this thesis introduces two novel processes for manufacturing hybrid and hierarchical silicon nanomaterials: (a) 1D nanostructure fabrication via thin-film dewetting and electrochemical etching, and (b) arbitrary-shaped 3D surfaces via direct electrochemical imprinting. Uniquely, they offer 3D dimensional control with sub-20 nm lateral and vertical resolution, mirror surface finish (i.e. RMS 20), low-defect density (i.e. no porous formation), and large-area patterning (>1 cm2). In each of these approaches, a fundamental understanding of ionic diffusion, reaction kinetics, and nucleation dynamics are directly correlated to manufacturing outputs - such as morphology defect density, material removal rate, patterning fidelity and resolution. Three scientific contributions have been made to the existing literature: (a) correlating electrochemical rate of reduction and oxidation to sidewall profiling in catalyst-based etching of silicon, (b) evidencing of diffusion limitations in solid metal catalysts, and (c) measuring the effect of porous substrate and catalysts in controlling the morphology of MACE-fabricated nanostructures. Overall, the techniques developed in this thesis bypass the need for dry etching and lithography, and are potentially compatible with amorphous and polycystalline silicon and III-V semiconductors. In turn, they may pave the way for the manufacturing of complex 3D hybrid objects on semiconductors for use in microoptics and nanophotonics, energy harvesting, and biosensing