RUI: Regenerative Electroless Etching for the Production of Si Nanostructures

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Applications of nanostructured silicon in, e.g., consumer products, nanomedicine and rechargeable batteries, would benefit from economical production of porous silicon powder on the kilogram-to-ton scale needed in new technologies essential for national prosperity. Electroless etching, which is an electrochemical process that is recognized possessing industrial potential but requiring advances in its reproducibility, controllability, purity, cost and scaling. This research will develop a new electrochemical process called regenerative electroless etching (ReEtching), a new concept in electroless wet etching with the capability of producing nanostructured and hierarchically structured semiconductors. ReEtching is a method in which one oxidant is used to continuously regenerate a low concentration of a second oxidant in the reaction mixture which is used in the reaction. These investigations will transform electroless etching from an irreproducible procedure into a process that can produce homogeneous porous films of arbitrary thickness, produce pillared particles of arbitrary length, produce either crystalline or amorphous pillars, produce hierarchical porous materials with nanopores inside of mesopores or nanopores inside of macropores. This work is carried out in a primarily undergraduate institution with strong international components providing the undergraduates involved in the research a unique international research experience.Regenerative electroless etching (ReEtching) is a electroless wet etching process with the capability of producing nanostructured and hierarchically structured semiconductors. ReEtching produces nanostructured semiconductors in a process which an oxidant (Ox1) is used as a catalytic agent to facilitate reaction between a semiconductor and a second oxidant (Ox2) that would be unreactive in the primary reaction. Ox2 is used to regenerate Ox1, which is capable of initiating etching. The extent of reaction is controlled by the amount of Ox2 added and the rate of reaction is controlled by the injection rate of Ox2. A specific example is the production of highly luminescent, nanocrystalline porous Si powder through reaction with V2O5 (the catalytic agent) and H2O2 (the regeneration agent) in HF(aq). Because it facilitates control the rate of reaction independent of the extent of reaction, ReEtching possesses previously unattainable processing capabilities. This grant will transform electroless etching from an irreproducible procedure into a process that can produce homogeneous porous films of arbitrary thickness, produce pillared particles of arbitrary length, produce either crystalline or amorphous pillars, produce hierarchical porous materials with nanopores inside of mesopores or nanopores inside of macropores. These meso-to-nanostructures will be characterized by photoluminescence and correlated with the materials structural parameters. Extension to other semiconductors will be developed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.