Regenerative electroless etching (ReEtching) uses a small amount of one oxidant, e.g. VO2+, and injection of a second oxidant, e.g. H2O2, with a syringe pump. VO2+ couples optimally to the Si valence band to initiate etching. Injection of H2O2 regenerates VO2+ and establishes a steady-state etch rate that spontaneously forms nanostructures. The syringe pump acts like a potentiostat in that the reaction rate (i.e. current) is determined by rate of H2O2 injection, extent of reaction (i.e. total charge passed) is controlled by amount of H2O2 injected, and electrochemical potential is set by the Nernstian relationship between E°(VO2+/VO2+), VO2+/VO2+ concentration ratio, and pH. Unlike previous methods, ReEtching porosifies particles completely to the core and is more efficient, channeling etching into the formation of photoluminescent Si with ~4 nm pores rather than reducing particle size. ReEtching porosifies Si of arbitrary size, shape and doping, including wafers, single-crystal powders, polycrystalline powders, metallurgical grade powder, Si nanowires (SiNW), Si pillars and Si powders that have been textured with MACE or formed by pulverizing anodized porous Si films. Injection of reagents also improves control and yield in metal assisted catalytic etching (MACE). In conventional MACE with a large amount of Ag, the catalytic etching is primarily localized below the Ag nanoparticles. Nanoparticle motion is highly correlated with each other. Etch track pores (width &gt; 60 nm) NOT Si nanowires (SiNW) are produced directly by MACE of powders. SiNWs form when a porosified layers is cleaved by capillary forces or sonication. Decreasing the Ag loaded onto the particles by 2 orders of magnitude, MACE enters a new regime (low-load MACE) in which pores with two distinctly different size distributions are formed peaking at ~4 nm and 10–40 nm. Etching results from a combination of small uncorrelated etch track pores as well as remote etching. Hierarchically nanostructured Si particles can be formed by combining ReEtching, MACE, electrochemical anodization and laser ablation. The high specific surface area of nanoporous Si facilitates production of porous Si nanoparticles terminated with hydrocarbons by means of ball milling or laser ablation in liquid organic solvents.

Changing the nature of electroless etching with a syringe pump: ReEtching, MACE and low load MACE

2019 Fall National Meeting

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